Climate sensitivity

<h2 id="fundamentals">Fundamentals</h2>
The rate at which energy reaches Earth as sunlight and leaves Earth as heat radiation to space <a href="/facts/Radiation_budget/PHytQRdx">must balance</a>, or the total amount of heat energy on the planet at any one time will rise or fall, which results in a planet that is warmer or cooler overall. A driver of an imbalance between the rates of incoming and outgoing radiation energy is called <a href="/facts/Radiative_forcing/VSLpzv66">radiative forcing</a>. A warmer planet <a href="/facts/Black-body_radiation/K4YKPKXL">radiates heat to space faster</a> and so a new balance is eventually reached, with a higher temperature and <a href="/facts/Ocean_heat_content/RDwuuFnm">stored energy content</a>. However, the warming of the planet also has <a href="/facts/Climate_feedbacks/rEN4BDE7">knock-on effects</a>, which create further warming in an <a href="/facts/Exacerbating_feedback/eFGatCpF">exacerbating feedback</a> loop. Climate sensitivity is a measure of how much temperature change a given amount of radiative forcing will cause.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> 

<h3>Radiative forcing</h3>
Main articles: <a href="/facts/Radiative_forcing/VSLpzv66">Radiative forcing</a> and <a href="/facts/Earth%27s_energy_imbalance/PHytQRdx">Earth's energy imbalance</a>
Radiative forcings are generally quantified as <a href="/facts/Watt/VK8oqRrm">Watts</a> per square meter (W/m2) and averaged over Earth's uppermost surface defined as the <a href="/facts/Tropopause/26rub4PU">top of the atmosphere</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The magnitude of a forcing is specific to the physical driver and is defined relative to an accompanying time span of interest for its application.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> In the context of a contribution to long-term climate sensitivity from 1750 to 2020, the 50% increase in atmospheric CO2 is characterized by a forcing of about +2.1 W/m2.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> In the context of shorter-term contributions to Earth's energy imbalance (i.e. its heating/cooling rate), time intervals of interest may be as short as the interval between measurement or simulation data samplings, and are thus likely to be accompanied by smaller forcing values. Forcings from such investigations have also been analyzed and reported at decadal time scales.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a><a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>
Radiative forcing leads to long-term changes in global temperature.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> A number of factors contribute radiative forcing: increased <a href="/facts/Downwelling/y4ep6Gyy">downwelling</a> radiation from the <a href="/facts/Greenhouse_effect/LGdNYYj3">greenhouse effect</a>, variability in solar radiation from <a href="/facts/Milankovitch_cycles/SxLbHrWX">changes in planetary orbit</a>, changes in <a href="/facts/Solar_irradiance/SI26I7aD">solar irradiance</a>, direct and indirect effects caused by aerosols (for example changes in <a href="/facts/Albedo/TJDRdKEB">albedo</a> from cloud cover), and changes in land use (deforestation or the loss of reflective ice cover).<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> In contemporary research, radiative forcing by greenhouse gases is well understood. As of 2019<a href="https://en.wikipedia.org/w/index.php?title=Climate_sensitivity&action=edit">[update]</a>, large uncertainties remain for aerosols.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a><a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h3>Key numbers</h3>
Further information: <a href="/facts/Carbon_dioxide_in_Earth%27s_atmosphere/h6A4HSzy">Carbon dioxide in Earth's atmosphere</a> and <a href="/facts/Instrumental_temperature_record/sJC5uRQj">Instrumental temperature record</a>
<a href="/facts/Carbon_dioxide_in_Earth%27s_atmosphere/h6A4HSzy">Carbon dioxide</a> (CO2) levels rose from 280 <a href="/facts/Parts_per_million/PozRuoLM">parts per million</a> (ppm) in the 18th century, when humans in the <a href="/facts/Industrial_Revolution/B6E3Fasm">Industrial Revolution</a> started burning significant amounts of fossil fuel such as coal, to over 415 ppm by 2020. As CO2 is a <a href="/facts/Greenhouse_gas/HXaHqrT8">greenhouse gas</a>, it hinders heat energy from leaving the Earth's atmosphere. In 2016, atmospheric CO2 levels had increased by 45% over preindustrial levels, and radiative forcing caused by increased CO2 was already more than 50% higher than in pre-industrial times because of non-linear effects.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a><a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> Between the 18th-century start of the Industrial Revolution and the year 2020, the Earth's temperature rose by a little over one degree Celsius (about two degrees Fahrenheit).<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h3>Societal importance</h3>
Because the <a href="/facts/Economics_of_climate_change_mitigation/Bd0As4P0">economics of climate change mitigation</a> depend greatly on how quickly <a href="/facts/Carbon_neutrality/llsAknfI">carbon neutrality</a> needs to be achieved, climate sensitivity estimates can have important economic and policy-making implications. One study suggests that halving the uncertainty of the value for transient climate response (TCR) could save trillions of dollars.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> A higher climate sensitivity would mean more dramatic increases in temperature, which makes it more prudent to take significant climate action.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a> If climate sensitivity turns out to be on the high end of what scientists estimate, the <a href="/facts/Paris_Agreement/hfIXBN1W">Paris Agreement</a> goal of limiting global warming to well below 2 °C cannot be achieved, and temperature increases will exceed that limit, at least temporarily. One study estimated that emissions cannot be reduced fast enough to meet the 2 °C goal if equilibrium climate sensitivity (the long-term measure) is higher than 3.4 °C (6.1 °F).<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a> The more sensitive the climate system is to changes in greenhouse gas concentrations, the more likely it is to have decades when temperatures are much higher or much lower than the longer-term average.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a><a class="footnote-ref" id="fnref:22" href="#fn:22">22</a>

<h2 id="factors-that-determine-sensitivity">Factors that determine sensitivity</h2>
The radiative forcing caused by a doubling of atmospheric CO2 levels (from the pre-industrial 280 ppm) is approximately 3.7 <a href="/facts/Watt/VK8oqRrm">watts</a> per square meter (W/m2). In the absence of feedbacks, the energy imbalance would eventually result in roughly 1 °C (1.8 °F) of <a href="/facts/Global_warming/rEN4BDE7">global warming</a>. That figure is straightforward to calculate by using the <a href="/facts/Stefan%E2%80%93Boltzmann_law/vA4tbwKC">Stefan–Boltzmann law</a><a class="footnote-ref" id="fnref:23" href="#fn:23">23</a><a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> and is undisputed.<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a>
A further contribution arises from <a href="/facts/Climate_change_feedback/N4nHNlPo">climate feedbacks</a>, both <a href="/facts/Exacerbating_feedback/eFGatCpF">self-reinforcing</a> and <a href="/facts/Suppressing_feedback/G9byVgpN">balancing</a>.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a><a class="footnote-ref" id="fnref:27" href="#fn:27">27</a> The uncertainty in climate sensitivity estimates is entirely from the modelling of feedbacks in the climate system, including <a href="/facts/Water_vapor_feedback/HXaHqrT8">water vapour feedback</a>, <a href="/facts/Ice%E2%80%93albedo_feedback/12TPLsJc">ice–albedo feedback</a>, <a href="/facts/Cloud_feedback/ntjAzFor">cloud feedback</a>, and <a href="/facts/Lapse_rate/FNyP1EjM">lapse rate</a> feedback.<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a> Balancing feedbacks tend to counteract warming by increasing the rate at which energy is radiated to space from a warmer planet. Exacerbating feedbacks increase warming; for example, higher temperatures can cause ice to melt, which reduces the ice area and the amount of sunlight the ice reflects, which in turn results in less heat energy being radiated back into space. Climate sensitivity depends on the balance between those feedbacks.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a>

<h2 id="types">Types</h2>
Depending on the time scale, there are two main ways to define climate sensitivity: the short-term transient climate response (TCR) and the long-term equilibrium climate sensitivity (ECS), both of which incorporate the warming from <a href="/facts/Exacerbating_feedback/eFGatCpF">exacerbating feedback</a> loops. They are not discrete categories, but they overlap. Sensitivity to atmospheric CO2 increases is measured in the amount of temperature change for doubling in the atmospheric CO2 concentration.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a><a class="footnote-ref" id="fnref:31" href="#fn:31">31</a>
Although the term "climate sensitivity" is usually used for the sensitivity to radiative forcing caused by rising atmospheric CO2, it is a general property of the climate system. Other agents can also cause a radiative imbalance. Climate sensitivity is the change in surface air temperature per unit change in radiative forcing, and the climate sensitivity parameter<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> is therefore expressed in units of °C/(W/m2). Climate sensitivity is approximately the same whatever the reason for the radiative forcing (such as from <a href="/facts/Greenhouse_gases/HXaHqrT8">greenhouse gases</a> or <a href="/facts/Solar_variation/QrP4Egea">solar variation</a>).<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a> When climate sensitivity is expressed as the temperature change for a level of atmospheric CO2 double the pre-industrial level, its units are <a href="/facts/Degrees_Celsius/okAEu1CA">degrees Celsius</a> (°C).

<h3>Transient climate response</h3>
Further information: <a href="/facts/Transient_climate_response_to_cumulative_carbon_emissions/f2Bo98br">Transient climate response to cumulative carbon emissions</a>
The transient climate response (TCR) is defined as "the change in the global mean surface temperature, averaged over a 20-year period, centered at the time of atmospheric carbon dioxide doubling, in a climate model simulation" in which the atmospheric CO2 concentration increases at 1% per year.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a> That estimate is generated by using shorter-term simulations.<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a> The transient response is lower than the equilibrium climate sensitivity because slower feedbacks, which exacerbate the temperature increase, take more time to respond in full to an increase in the atmospheric CO2 concentration. For instance, the deep ocean takes many centuries to reach a new steady state after a perturbation during which it continues to serve as <a href="/facts/Heatsink/ccIEdHnq">heatsink</a>, which cools the upper ocean.<a class="footnote-ref" id="fnref:36" href="#fn:36">36</a> The IPCC literature assessment estimates that the TCR likely lies between 1 °C (1.8 °F) and 2.5 °C (4.5 °F).<a class="footnote-ref" id="fnref:37" href="#fn:37">37</a>
A related measure is the <a href="/facts/Transient_climate_response_to_cumulative_carbon_emissions/f2Bo98br">transient climate response to cumulative carbon emissions</a> (TCRE), which is the globally averaged surface temperature change after 1000 GtC of CO2 has been emitted.<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a> As such, it includes not only temperature feedbacks to forcing but also the <a href="/facts/Carbon_cycle/gVusRaPF">carbon cycle</a> and carbon cycle feedbacks.<a class="footnote-ref" id="fnref:39" href="#fn:39">39</a>

<h3>Equilibrium climate sensitivity</h3>
The equilibrium climate sensitivity (ECS) is the long-term temperature rise (equilibrium <a href="/facts/Global_surface_temperature/oddUmrb4">global mean near-surface air temperature</a>) that is expected to result from a doubling of the atmospheric CO2 concentration (ΔT2×). It is a prediction of the new global mean near-surface air temperature once the CO2 concentration has stopped increasing, and most of the feedbacks have had time to have their full effect. Reaching an equilibrium temperature can take centuries or even millennia after CO2 has doubled. ECS is higher than TCR because of the oceans' short-term buffering effects.<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a> Computer models are used for estimating the ECS.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a> A comprehensive estimate means that modelling the whole time span during which significant feedbacks continue to change global temperatures in the model, such as fully-equilibrating ocean temperatures, requires running a computer model that covers thousands of years. There are, however, less <a href="/facts/Data-intensive_computing/BhQMlqq8">computing-intensive methods</a>.<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a>
The <a href="/facts/IPCC_Sixth_Assessment_Report/Dc5drLUK">IPCC Sixth Assessment Report</a> (AR6) stated that there is high confidence that ECS is within the range of 2.5 °C to 4 °C, with a best estimate of 3 °C.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a>
The long time scales involved with ECS make it arguably a less relevant measure for policy decisions around climate change.<a class="footnote-ref" id="fnref:44" href="#fn:44">44</a>

<h4>Effective climate sensitivity</h4>
A common approximation to ECS is the effective equilibrium climate sensitivity, is an estimate of equilibrium climate sensitivity by using data from a climate system in model or real-world observations that is not yet in equilibrium.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a> Estimates assume that the net amplification effect of feedbacks, as measured after some period of warming, will remain constant afterwards.<a class="footnote-ref" id="fnref:46" href="#fn:46">46</a> That is not necessarily true, as <a href="/facts/Tipping_points_in_the_climate_system/fpPR0g5I">feedbacks can change with time</a>.<a class="footnote-ref" id="fnref:47" href="#fn:47">47</a><a class="footnote-ref" id="fnref:48" href="#fn:48">48</a> In many climate models, feedbacks become stronger over time and so the effective climate sensitivity is lower than the real ECS.<a class="footnote-ref" id="fnref:49" href="#fn:49">49</a>

<h3>Earth system sensitivity</h3>
By definition, equilibrium climate sensitivity does not include feedbacks that take millennia to emerge, such as long-term changes in Earth's albedo because of changes in ice sheets and vegetation. It includes the slow response of the deep oceans' warming, which also takes millennia, and so ECS fails to reflect the actual future warming that would occur if CO2 is stabilized at double pre-industrial values.<a class="footnote-ref" id="fnref:50" href="#fn:50">50</a> Earth system sensitivity (ESS) incorporates the effects of these slower feedback loops, such as the change in Earth's <a href="/facts/Albedo/TJDRdKEB">albedo</a> from the melting of large continental <a href="/facts/Ice_sheets/j3QpYSeK">ice sheets</a>, which covered much of the Northern Hemisphere during the <a href="/facts/Last_Glacial_Maximum/BXQyc9IP">Last Glacial Maximum</a> and still cover <a href="/facts/Greenland/aagXRTB7">Greenland</a> and <a href="/facts/Antarctica/bEM5Lem5">Antarctica</a>). Changes in albedo as a result of changes in vegetation, as well as changes in ocean circulation, are also included.<a class="footnote-ref" id="fnref:51" href="#fn:51">51</a><a class="footnote-ref" id="fnref:52" href="#fn:52">52</a> The longer-term feedback loops make the ESS larger than the ECS, possibly twice as large. Data from the <a href="/facts/Geological_history_of_Earth/Jx7ClmF4">geological history of Earth</a> is used in estimating ESS. Differences between modern and long-ago climatic conditions mean that estimates of the future ESS are highly uncertain.<a class="footnote-ref" id="fnref:53" href="#fn:53">53</a> Unlike ECS and TCR, the <a href="/facts/Carbon_cycle/gVusRaPF">carbon cycle</a> is not included in the definition of the ESS, but all other elements of the climate system are included.<a class="footnote-ref" id="fnref:54" href="#fn:54">54</a>

<h2 id="sensitivity-to-nature-of-forcing">Sensitivity to nature of forcing</h2>
Different forcing agents, such as greenhouse gases and aerosols, can be compared using their radiative forcing, the initial radiative imbalance averaged over the entire globe. Climate sensitivity is the amount of warming per radiative forcing. To a first approximation, the cause of the radiative imbalance does not matter whether it is greenhouse gases or something else. However, radiative forcing from sources other than CO2 can cause a somewhat larger or smaller surface warming than a similar radiative forcing from CO2. The amount of feedback varies mainly because the forcings are not uniformly distributed over the globe. Forcings that initially warm the Northern Hemisphere, land, or <a href="/facts/Polar_regions_of_Earth/KkBuzr2n">polar regions</a> are more strongly systematically effective at changing temperatures than an equivalent forcing from CO2, which is more uniformly distributed over the globe. That is because those regions have more self-reinforcing feedbacks, such as the ice–albedo feedback. Several studies indicate that human-emitted aerosols are more effective than CO2 at changing global temperatures, and volcanic forcing is less effective.<a class="footnote-ref" id="fnref:55" href="#fn:55">55</a> When climate sensitivity to CO2 forcing is estimated by using historical temperature and forcing (caused by a mix of aerosols and greenhouse gases), and that effect is not taken into account, climate sensitivity is underestimated.<a class="footnote-ref" id="fnref:56" href="#fn:56">56</a>

<h2 id="state-dependence">State dependence</h2>

Climate sensitivity has been defined as the short- or long-term temperature change resulting from any doubling of CO2, but there is evidence that the sensitivity of Earth's climate system is not constant. For instance, the planet has <a href="/facts/Polar_ice_cap/D8LNoYyb">polar ice</a> and high-altitude <a href="/facts/Glaciers/8GrKVUSS">glaciers</a>. Until the world's ice has completely melted, an exacerbating <a href="/facts/Ice%E2%80%93albedo_feedback/12TPLsJc">ice–albedo feedback</a> loop makes the system more sensitive overall.<a class="footnote-ref" id="fnref:57" href="#fn:57">57</a> Throughout Earth's history, multiple periods are thought to have snow and ice cover almost the entire globe. In most models of "Snowball Earth", parts of the tropics were at least intermittently free of ice cover. As the ice advanced or retreated, climate sensitivity must have been very high, as the large changes in area of ice cover would have made for a very strong <a href="/facts/Ice%E2%80%93albedo_feedback/12TPLsJc">ice–albedo feedback</a>. Volcanic atmospheric composition changes are thought to have provided the radiative forcing needed to escape the snowball state.<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a>

Throughout the <a href="/facts/Quaternary_period/3cEgHAqc">Quaternary period</a> (the most recent 2.58 million years), climate has oscillated between <a href="/facts/Glacial_period/alIAm38r">glacial periods</a>, the most recent one being the <a href="/facts/Last_Glacial_Maximum/BXQyc9IP">Last Glacial Maximum</a>, and <a href="/facts/Interglacial_period/gKf9Br27">interglacial periods</a>, the most recent one being the current <a href="/facts/Holocene/sppPgwW5">Holocene</a>, but the period's climate sensitivity is difficult to determine. The <a href="/facts/Paleocene%E2%80%93Eocene_Thermal_Maximum/QnPVzRR7">Paleocene–Eocene Thermal Maximum</a>, about 55.5 million years ago, was unusually warm and may have been characterized by above-average climate sensitivity.<a class="footnote-ref" id="fnref:59" href="#fn:59">59</a>
Climate sensitivity may further change if tipping points are crossed. It is unlikely that tipping points will cause short-term changes in climate sensitivity. If a tipping point is crossed, climate sensitivity is expected to change at the time scale of the subsystem that hits its tipping point. Especially if there are multiple interacting tipping points, the transition of climate to a new state may be difficult to reverse.<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a>
The two most common definitions of climate sensitivity specify the climate state: the ECS and the TCR are defined for a doubling with respect to the CO2 levels in the pre-industrial era. Because of potential changes in climate sensitivity, the climate system may warm by a different amount after a second doubling of CO2 from after a first doubling. The effect of any change in climate sensitivity is expected to be small or negligible in the first century after additional CO2 is released into the atmosphere.<a class="footnote-ref" id="fnref:61" href="#fn:61">61</a>

<h2 id="estimation">Estimation</h2>
<h3>Using Industrial Age (1750–present) data</h3>
Climate sensitivity can be estimated using the observed temperature increase, the observed <a href="/facts/Ocean_heat_content/RDwuuFnm">ocean heat uptake</a>, and the modelled or observed radiative forcing. The data are linked through a simple energy-balance model to calculate climate sensitivity.<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a> Radiative forcing is often modelled because <a href="/facts/Earth_observation_satellite/WK2zGRSV">Earth observation satellites</a> measuring it has existed during only part of the Industrial Age (only since the late 1950s). Estimates of climate sensitivity calculated by using these global energy constraints have consistently been lower than those calculated by using other methods,<a class="footnote-ref" id="fnref:63" href="#fn:63">63</a> around 2 °C (3.6 °F) or lower.<a class="footnote-ref" id="fnref:64" href="#fn:64">64</a><a class="footnote-ref" id="fnref:65" href="#fn:65">65</a><a class="footnote-ref" id="fnref:66" href="#fn:66">66</a><a class="footnote-ref" id="fnref:67" href="#fn:67">67</a>
Estimates of transient climate response (TCR) that have been calculated from models and observational data can be reconciled if it is taken into account that fewer temperature measurements are taken in the polar regions, which <a href="/facts/Polar_amplification/MaJEHgVW">warm more quickly than the Earth as a whole</a>. If only regions for which measurements are available are used in evaluating the model, the differences in TCR estimates are negligible.<a class="footnote-ref" id="fnref:68" href="#fn:68">68</a><a class="footnote-ref" id="fnref:69" href="#fn:69">69</a>
A very simple climate model could estimate climate sensitivity from Industrial Age data<a class="footnote-ref" id="fnref:70" href="#fn:70">70</a> by waiting for the climate system to reach equilibrium and then by measuring the resulting warming, ΔTeq (°C). Computation of the equilibrium climate sensitivity, S (°C), using the radiative forcing ΔF (W/m2) and the measured temperature rise, would then be possible. The radiative forcing resulting from a doubling of CO2, F2
 
 
 
 ×
 
 
 {\displaystyle \times }
 
CO2, is relatively well known, at about 3.7 W/m2. Combining that information results in this equation:

S
 =
 Δ
 
 T
 
 e
 q
 
 
 ×
 
 F
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 
 /
 
 Δ
 F
 
 
 {\displaystyle S=\Delta T_{eq}\times F_{2\times CO_{2}}/\Delta F}
 
.
However, the climate system is not in equilibrium since the actual warming lags the equilibrium warming, largely because the oceans take up heat and will take centuries or millennia to reach equilibrium.<a class="footnote-ref" id="fnref:71" href="#fn:71">71</a> Estimating climate sensitivity from Industrial Age data requires an adjustment to the equation above. The actual forcing felt by the atmosphere is the radiative forcing minus the ocean's heat uptake, H (W/m2) and so climate sensitivity can be estimated:

S
        =
        Δ
        T
        ×
        
          F
          
            2
            ×
            C
            
              O
              
                2
              
            
          
        
        
          /
        
        (
        Δ
        F
        −
        H
        )
        .
      
    
    {\displaystyle S=\Delta T\times F_{2\times CO_{2}}/(\Delta F-H).}

The global temperature increase between the beginning of the Industrial Period, which is (<a href="/facts/History_of_coal_mining/0A13g44s">taken as 1750</a>, and 2011 was about 0.85 °C (1.53 °F). In 2011, the radiative forcing from CO2 and other long-lived greenhouse gases (mainly <a href="/facts/Methane/kBHneYnh">methane</a>, <a href="/facts/Nitrous_oxide/Jvys91lI">nitrous oxide</a>, and <a href="/facts/Chlorofluorocarbon/uLApxm7K">chlorofluorocarbon</a>) that have been emitted since the 18th century was roughly 2.8 W/m2. The climate forcing, ΔF, also contains contributions from solar activity (+0.05 W/m2), aerosols (−0.9 W/m2), ozone (+0.35 W/m2), and other smaller influences, which brings the total forcing over the Industrial Period to 2.2 W/m2, according to the best estimate of the <a href="/facts/IPCC_Fifth_Assessment_Report/aYz6LE8H">IPCC Fifth Assessment Report</a> in 2014, with substantial uncertainty.<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a> The ocean heat uptake, estimated by the same report to be 0.42 W/m2,<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a> yields a value for S of 1.8 °C (3.2 °F).

<h4>Other strategies</h4>
In theory, Industrial Age temperatures could also be used to determine a time scale for the temperature response of the climate system and thus climate sensitivity:<a class="footnote-ref" id="fnref:74" href="#fn:74">74</a> if the effective <a href="/facts/Heat_capacity/I63nzSyp">heat capacity</a> of the climate system is known, and the timescale is estimated using <a href="/facts/Autocorrelation/dm4MqK0A">autocorrelation</a> of the measured temperature, an estimate of climate sensitivity can be derived. In practice, however, the simultaneous determination of the time scale and heat capacity is difficult.<a class="footnote-ref" id="fnref:75" href="#fn:75">75</a><a class="footnote-ref" id="fnref:76" href="#fn:76">76</a><a class="footnote-ref" id="fnref:77" href="#fn:77">77</a>
Attempts have been made to use the 11-year <a href="/facts/Solar_cycle/QrP4Egea">solar cycle</a> to constrain the transient climate response.<a class="footnote-ref" id="fnref:78" href="#fn:78">78</a> <a href="/facts/Solar_irradiance/SI26I7aD">Solar irradiance</a> is about 0.9 W/m2 higher during a <a href="/facts/Solar_maximum/926z06yc">solar maximum</a> than during a <a href="/facts/Solar_minimum/29ooEQBD">solar minimum</a>, and those effect can be observed in measured average global temperatures from 1959 to 2004.<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a> Unfortunately, the solar minima in the period coincided with volcanic eruptions, which <a href="/facts/Volcanic_winter/SAnA3nsU">have a cooling effect on the global temperature</a>. Because the eruptions caused a larger and less well-quantified decrease in radiative forcing than the reduced solar irradiance, it is questionable whether useful quantitative conclusions can be derived from the observed temperature variations.<a class="footnote-ref" id="fnref:80" href="#fn:80">80</a>
Observations of volcanic eruptions have also been used to try to estimate climate sensitivity, but as the aerosols from a single eruption last at most a couple of years in the atmosphere, the climate system can never come close to equilibrium, and there is less cooling than there would be if the aerosols stayed in the atmosphere for longer. Therefore, volcanic eruptions give information only about a <a href="/facts/Upper_and_lower_bounds/YJje9oC2">lower bound</a> on transient climate sensitivity.<a class="footnote-ref" id="fnref:81" href="#fn:81">81</a>

<h3>Using data from Earth's past</h3>
Historical climate sensitivity can be estimated by using <a href="/facts/Proxy_(climate)/kuCVBpBL">reconstructions</a> of Earth's past temperatures and CO2 levels. <a href="/facts/Paleoclimatologists/p3x22QaC">Paleoclimatologists</a> have studied different geological periods, such as the warm <a href="/facts/Pliocene_climate/nMI9tRpX">Pliocene</a> (5.3 to 2.6 million years ago) and the colder <a href="/facts/Pleistocene/0ya9eUp5">Pleistocene</a> (2.6 million to 11,700 years ago),<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a> and sought periods that are in some way analogous to or informative about current climate change. Climates further back in Earth's history are more difficult to study because fewer data are available about them. For instance, past CO2 concentrations can be <a href="/facts/Ice_core/QnzraAoN">derived from air trapped in ice cores</a>, but as of 2020<a href="https://en.wikipedia.org/w/index.php?title=Climate_sensitivity&action=edit">[update]</a>, the oldest continuous ice core is less than one million years old.<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a> Recent periods, such as the <a href="/facts/Last_Glacial_Maximum/BXQyc9IP">Last Glacial Maximum</a> (LGM) (about 21,000 years ago) and the <a href="/facts/Holocene_climatic_optimum/tsALYMFp">Mid-Holocene</a> (about 6,000 years ago), are often studied, especially when more information about them becomes available.<a class="footnote-ref" id="fnref:84" href="#fn:84">84</a><a class="footnote-ref" id="fnref:85" href="#fn:85">85</a>
A 2007 estimate of sensitivity made using data from the most recent 420 million years is consistent with sensitivities of current climate models and with other determinations.<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a> The <a href="/facts/Paleocene%E2%80%93Eocene_Thermal_Maximum/QnPVzRR7">Paleocene–Eocene Thermal Maximum</a> (about 55.5 million years ago), a 20,000-year period during which massive amount of carbon entered the atmosphere and average global temperatures increased by approximately 6 °C (11 °F), also provides a good opportunity to study the climate system when it was in a warm state.<a class="footnote-ref" id="fnref:87" href="#fn:87">87</a> Studies of the last 800,000 years have concluded that climate sensitivity was greater in <a href="/facts/Glacial_periods/alIAm38r">glacial periods</a> than in interglacial periods.<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a>
As the name suggests, the Last Glacial Maximum was much colder than today, and good data on atmospheric CO2 concentrations and radiative forcing from that period are available.<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a> The period's <a href="/facts/Orbital_forcing/8je0aXJ8">orbital forcing</a> was different from today's but had little effect on mean annual temperatures.<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a> Estimating climate sensitivity from the Last Glacial Maximum can be done by several different ways.<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a> One way is to use estimates of global radiative forcing and temperature directly. The set of feedback mechanisms active during the period, however, may be different from the feedbacks caused by a present doubling of CO2,<a class="footnote-ref" id="fnref:92" href="#fn:92">92</a> which introduces additional uncertainty.<a class="footnote-ref" id="fnref:93" href="#fn:93">93</a><a class="footnote-ref" id="fnref:94" href="#fn:94">94</a> In a different approach, a model of intermediate complexity is used to simulate conditions during the period. Several versions of this single model are run, with different values chosen for uncertain parameters, such that each version has a different ECS. Outcomes that best simulate the LGM's observed cooling probably produce the most realistic ECS values.<a class="footnote-ref" id="fnref:95" href="#fn:95">95</a>

<h3>Using climate models</h3>

<a href="/facts/Climate_model/5xQBYLcl">Climate models</a> simulate the CO2-driven warming of the future as well as the past. They operate on principles similar to those underlying <a href="/facts/Numerical_weather_prediction/TXdbEfE4">models that predict the weather</a>, but they focus on longer-term processes. Climate models typically begin with a starting state and then apply physical laws and knowledge about biology to generate subsequent states. As with weather modelling, no computer has the power to model the complexity of the entire planet and so simplifications are used to reduce that complexity to something manageable. An important simplification divides Earth's atmosphere into model cells. For instance, the atmosphere might be divided into cubes of air ten or one hundred kilometers on a side. Each model cell is treated as if it were <a href="/facts/Homogeneous/y84KQJxl">homogeneous</a>. Calculations for model cells are much faster than trying to simulate each molecule of air separately.<a class="footnote-ref" id="fnref:96" href="#fn:96">96</a>
A lower <a href="/facts/Microscale_and_macroscale_models/xUQHCYKr">model resolution</a> (large model cells and long time steps) takes less computing power but cannot simulate the atmosphere in as much detail. A model cannot simulate processes smaller than the model cells or shorter-term than a single time step. The effects of the smaller-scale and shorter-term processes must therefore be estimated by using other methods. Physical laws contained in the models may also be simplified to speed up calculations. The <a href="/facts/Biosphere/P1ltA4sb">biosphere</a> must be included in climate models. The effects of the biosphere are estimated by using data on the average behaviour of the average plant assemblage of an area under the modelled conditions. Climate sensitivity is therefore an <a href="/facts/Emergent_property/gLAd6wda">emergent property</a> of these models. It is not prescribed, but it follows from the interaction of all the modelled processes.<a class="footnote-ref" id="fnref:97" href="#fn:97">97</a>
To estimate climate sensitivity, a model is run by using a variety of radiative forcings (doubling quickly, doubling gradually, or following historical emissions) and the temperature results are compared to the forcing applied. Different models give different estimates of climate sensitivity, but they tend to fall within a similar range, as described above.

<h4>Testing, comparisons, and climate ensembles</h4>
Modelling of the climate system can lead to a wide range of outcomes. Models are often run that use different plausible parameters in their approximation of physical laws and the behaviour of the biosphere, which forms a <a href="/facts/Climate_ensemble/rgsm0E8t">perturbed physics ensemble</a>, which attempts to model the sensitivity of the climate to different types and amounts of change in each parameter. Alternatively, structurally-different models developed at different institutions are put together, creating an ensemble. By selecting only the simulations that can simulate some part of the historical climate well, a constrained estimate of climate sensitivity can be made. One strategy for obtaining more accurate results is placing more emphasis on climate models that perform well in general.<a class="footnote-ref" id="fnref:98" href="#fn:98">98</a>
A model is tested using observations, paleoclimate data, or both to see if it replicates them accurately. If it does not, inaccuracies in the physical model and parametrizations are sought, and the model is modified. For models used to estimate climate sensitivity, specific test metrics that are directly and physically linked to climate sensitivity are sought. Examples of such metrics are the global patterns of warming,<a class="footnote-ref" id="fnref:99" href="#fn:99">99</a> the ability of a model to reproduce observed relative humidity in the tropics and subtropics,<a class="footnote-ref" id="fnref:100" href="#fn:100">100</a> patterns of heat radiation,<a class="footnote-ref" id="fnref:101" href="#fn:101">101</a> and the variability of temperature around long-term historical warming.<a class="footnote-ref" id="fnref:102" href="#fn:102">102</a><a class="footnote-ref" id="fnref:103" href="#fn:103">103</a><a class="footnote-ref" id="fnref:104" href="#fn:104">104</a> Ensemble climate models developed at different institutions tend to produce constrained estimates of ECS that are slightly higher than 3 °C (5.4 °F). The models with ECS slightly above 3 °C (5.4 °F) simulate the above situations better than models with a lower climate sensitivity.<a class="footnote-ref" id="fnref:105" href="#fn:105">105</a>
Many projects and groups exist to compare and to analyse the results of multiple models. For instance, the <a href="/facts/Coupled_Model_Intercomparison_Project/rImqdYS3">Coupled Model Intercomparison Project</a> (CMIP) has been running since the 1990s.<a class="footnote-ref" id="fnref:106" href="#fn:106">106</a>

<h3>Historical estimates</h3>
<a href="/facts/Svante_Arrhenius/S2rlyzYr">Svante Arrhenius</a> in the 19th century was the first person to quantify global warming as a consequence of a doubling of the concentration of CO2. In his first paper on the matter, he estimated that global temperature would rise by around 5 to 6 °C (9.0 to 10.8 °F) if the quantity of CO2 was doubled. In later work, he revised that estimate to 4 °C (7.2 °F).<a class="footnote-ref" id="fnref:107" href="#fn:107">107</a> Arrhenius used <a href="/facts/Samuel_Pierpont_Langley/jHj588ru">Samuel Pierpont Langley</a>'s observations of radiation emitted by the full moon to estimate the amount of radiation that was absorbed by <a href="/facts/Water_vapour/DX5IUFG0">water vapour</a> and by CO2. To account for water vapour feedback, he assumed that <a href="/facts/Relative_humidity/Nwb28VlT">relative humidity</a> would stay the same under global warming.<a class="footnote-ref" id="fnref:108" href="#fn:108">108</a><a class="footnote-ref" id="fnref:109" href="#fn:109">109</a>
The first calculation of climate sensitivity that used detailed measurements of <a href="/facts/Absorption_spectra/GH7RC14D">absorption spectra</a>, as well as the first calculation to use a <a href="/facts/Computer/SQe1aK05">computer</a> for <a href="/facts/Numerical_integration/MwJnvcDV">numerical integration</a> of the radiative transfer through the atmosphere, was performed by <a href="/facts/Syukuro_Manabe/cTsE9CeD">Syukuro Manabe</a> and Richard Wetherald in 1967.<a class="footnote-ref" id="fnref:110" href="#fn:110">110</a> Assuming constant humidity, they computed an equilibrium climate sensitivity of 2.3 °C per doubling of CO2, which they rounded to 2 °C, the value most often quoted from their work, in the abstract of the paper. The work has been called "arguably the greatest climate-science paper of all time"<a class="footnote-ref" id="fnref:111" href="#fn:111">111</a> and "the most influential study of climate of all time."<a class="footnote-ref" id="fnref:112" href="#fn:112">112</a>
A committee on anthropogenic <a href="/facts/Global_warming/rEN4BDE7">global warming</a>, convened in 1979 by the <a href="/facts/United_States_National_Academy_of_Sciences/M3oePVeG">United States National Academy of Sciences</a> and chaired by <a href="/facts/Jule_Charney/mIEuVaV7">Jule Charney</a>,<a class="footnote-ref" id="fnref:113" href="#fn:113">113</a> estimated equilibrium climate sensitivity to be 3 °C (5.4 °F), plus or minus 1.5 °C (2.7 °F). The Manabe and Wetherald estimate (2 °C (3.6 °F)), <a href="/facts/James_E._Hansen/z0A4PnM9">James E. Hansen</a>'s estimate of 4 °C (7.2 °F), and Charney's model were the only models available in 1979. According to Manabe, speaking in 2004, "Charney chose 0.5 °C as a reasonable margin of error, subtracted it from Manabe's number, and added it to Hansen's, giving rise to the 1.5 to 4.5 °C (2.7 to 8.1 °F) range of likely climate sensitivity that has appeared in every greenhouse assessment since ...."<a class="footnote-ref" id="fnref:114" href="#fn:114">114</a> In 2008, climatologist <a href="/facts/Stefan_Rahmstorf/W9yu34ag">Stefan Rahmstorf</a> said: "At that time [it was published], the [Charney report estimate's] range [of uncertainty] was on very shaky ground. Since then, many vastly improved models have been developed by a number of climate research centers around the world."<a class="footnote-ref" id="fnref:115" href="#fn:115">115</a>

<h3>Assessment reports of IPCC</h3>

Despite considerable progress in the understanding of Earth's <a href="/facts/Climate_system/5JyveutF">climate system</a>, assessments continued to report similar uncertainty ranges for climate sensitivity for some time after the 1979 Charney report.<a class="footnote-ref" id="fnref:116" href="#fn:116">116</a> The <a href="/facts/IPCC_First_Assessment_Report/b1X7PFQp">First Assessment Report</a> of the <a href="/facts/Intergovernmental_Panel_on_Climate_Change/sh76du1u">Intergovernmental Panel on Climate Change</a> (IPCC), published in 1990, estimated that equilibrium climate sensitivity to a doubling of CO2 lay between 1.5 and 4.5 °C (2.7 and 8.1 °F), with a "best guess in the light of current knowledge" of 2.5 °C (4.5 °F).<a class="footnote-ref" id="fnref:117" href="#fn:117">117</a> The report used models with simplified representations of <a href="/facts/Ocean_dynamics/85LpfFgk">ocean dynamics</a>. The <a href="/facts/IPCC_supplementary_report,_1992/eGcUfGMT">IPCC supplementary report, 1992</a>, which used full-ocean <a href="/facts/General_circulation_model/6QUar9RF">circulation models</a>, saw "no compelling reason to warrant changing" the 1990 estimate;<a class="footnote-ref" id="fnref:118" href="#fn:118">118</a> and the <a href="/facts/IPCC_Second_Assessment_Report/dh7q9AsV">IPCC Second Assessment Report</a> stated, "No strong reasons have emerged to change [these estimates],"<a class="footnote-ref" id="fnref:119" href="#fn:119">119</a> In the reports, much of the uncertainty around climate sensitivity was attributed to insufficient knowledge of cloud processes. The 2001 <a href="/facts/IPCC_Third_Assessment_Report/1DfXFCKF">IPCC Third Assessment Report</a> also retained this likely range.<a class="footnote-ref" id="fnref:120" href="#fn:120">120</a>
Authors of the 2007 <a href="/facts/IPCC_Fourth_Assessment_Report/s0pDYRt5">IPCC Fourth Assessment Report</a><a class="footnote-ref" id="fnref:121" href="#fn:121">121</a> stated that confidence in estimates of equilibrium climate sensitivity had increased substantially since the Third Annual Report.<a class="footnote-ref" id="fnref:122" href="#fn:122">122</a> The IPCC authors concluded that ECS is very likely to be greater than 1.5 °C (2.7 °F) and likely to lie in the range 2 to 4.5 °C (3.6 to 8.1 °F), with a most likely value of about 3 °C (5.4 °F). The IPCC stated that fundamental physical reasons and data limitations prevent a climate sensitivity higher than 4.5 °C (8.1 °F) from being ruled out, but the climate sensitivity estimates in the likely range agreed better with observations and the <a href="/facts/Proxy_(climate)/kuCVBpBL">proxy climate</a> data.<a class="footnote-ref" id="fnref:123" href="#fn:123">123</a>
The 2013 <a href="/facts/IPCC_Fifth_Assessment_Report/aYz6LE8H">IPCC Fifth Assessment Report</a> reverted to the earlier range of 1.5 to 4.5 °C (2.7 to 8.1 °F) (with high confidence), because some estimates using industrial-age data came out low.<a class="footnote-ref" id="fnref:124" href="#fn:124">124</a> The report also stated that ECS is extremely unlikely to be less than 1 °C (1.8 °F) (high confidence), and it is very unlikely to be greater than 6 °C (11 °F) (medium confidence). Those values were estimated by combining the available data with expert judgement.<a class="footnote-ref" id="fnref:125" href="#fn:125">125</a>
In preparation for the 2021 <a href="/facts/IPCC_Sixth_Assessment_Report/Dc5drLUK">IPCC Sixth Assessment Report</a>, a new generation of climate models was developed by scientific groups around the world.<a class="footnote-ref" id="fnref:126" href="#fn:126">126</a><a class="footnote-ref" id="fnref:127" href="#fn:127">127</a> Across 27 <a href="/facts/General_circulation_model/6QUar9RF">global climate models</a>, estimates of a higher climate sensitivity were produced. The values spanned 1.8 to 5.6 °C (3.2 to 10.1 °F) and exceeded 4.5 °C (8.1 °F) in 10 of them.<a class="footnote-ref" id="fnref:128" href="#fn:128">128</a><a class="footnote-ref" id="fnref:129" href="#fn:129">129</a> The estimates for equilibrium climate sensitivity changed from 3.2 °C to 3.7 °C and the estimates for the <a href="/facts/Transient_climate_response_to_cumulative_carbon_emissions/f2Bo98br">transient climate response</a> from 1.8 °C, to 2.0 °C.<a class="footnote-ref" id="fnref:130" href="#fn:130">130</a> The cause of the increased ECS lies mainly in improved modelling of clouds. Temperature rises are now believed to cause sharper decreases in the number of low clouds, and fewer low clouds means more sunlight is absorbed by the planet and less reflected to space.<a class="footnote-ref" id="fnref:131" href="#fn:131">131</a><a class="footnote-ref" id="fnref:132" href="#fn:132">132</a><a class="footnote-ref" id="fnref:133" href="#fn:133">133</a><a class="footnote-ref" id="fnref:134" href="#fn:134">134</a>
Remaining deficiencies in the simulation of clouds may have led to overestimates,<a class="footnote-ref" id="fnref:135" href="#fn:135">135</a> as models with the highest ECS values were not consistent with observed warming.<a class="footnote-ref" id="fnref:136" href="#fn:136">136</a> A fifth of the models began to 'run hot', predicting that global warming would produce significantly higher temperatures than is considered plausible.<a class="footnote-ref" id="fnref:137" href="#fn:137">137</a><a class="footnote-ref" id="fnref:138" href="#fn:138">138</a> According to these models, known as hot models, average global temperatures in the <a href="/facts/Climate_change_scenario/MCHKP59V">worst-case scenario</a> would rise by more than 5 °C above preindustrial levels by 2100,<a class="footnote-ref" id="fnref:139" href="#fn:139">139</a> with a "catastrophic" impact on human society.<a class="footnote-ref" id="fnref:140" href="#fn:140">140</a> In comparison, empirical observations combined with physics models indicate that the "very likely" range is between 2.3 and 4.7 °C. Models with a very high climate sensitivity are also known to be poor at reproducing known historical climate trends, such as warming over the 20th century or cooling during the <a href="/facts/Last_ice_age/acYQETg7">last ice age</a>.<a class="footnote-ref" id="fnref:141" href="#fn:141">141</a> For these reasons the predictions of hot models are considered implausible, and have been given less weight by the IPCC in 2022.<a class="footnote-ref" id="fnref:142" href="#fn:142">142</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Climate_risk/vJdUJpwI">Climate risk</a></li>
<li><a href="/facts/Charney_Report/2L6JK9XS">Charney Report</a></li></ul>
<h2 id="notes">Notes</h2>

<h3>Sources</h3>

Wikimedia Commons has media related to Climate sensitivity.

<ul><li>Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL, eds. (2007). <a href="http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html">Climate Change 2007: The Physical Science Basis</a>. Contribution of Working Group I to the <a href="/facts/IPCC_Fourth_Assessment_Report/s0pDYRt5">Fourth Assessment Report</a> of the Intergovernmental Panel on Climate Change. Cambridge University Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-521-88009-1. <a href="https://web.archive.org/web/20120605025550/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html">Archived</a> from the original on 5 June 2012. Retrieved 15 December 2012. (pb: 978-0-521-70596-7)</li>
<li><a href="/facts/IPCC/sh76du1u">IPCC</a> (2013). Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, et al. (eds.). <a href="http://www.climatechange2013.org/images/report/WG1AR5_ALL_FINAL.pdf">Climate Change 2013: The Physical Science Basis</a> (PDF). Contribution of Working Group I to the <a href="/facts/IPCC_Fifth_Assessment_Report/aYz6LE8H">Fifth Assessment Report</a> of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-107-05799-9. <a href="https://web.archive.org/web/20190925154911/http://www.climatechange2013.org/images/report/WG1AR5_ALL_FINAL.pdf">Archived</a> (PDF) from the original on 25 September 2019. Retrieved 15 February 2020. (pb: 978-1-107-66182-0).</li>
<li>Stocker TF, Qin D, Plattner GK, Alexander LV, Allen SK, Bindoff NL, et al. (2013). <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf">"Technical Summary"</a> (PDF). IPCC AR5 WG1 2013. pp. 33–115. <a href="https://web.archive.org/web/20191220130235/https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf">Archived</a> (PDF) from the original on 20 December 2019. Retrieved 12 February 2020.
<ul><li>Masson-Delmotte V, Schulz M, Abe-Ouchi A, Beer J, Ganopolski A, Rouco JG, et al. (2013). <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf">"Chapter 5: Information from Paleoclimate Archives"</a> (PDF). IPCC AR5 WG1 2013. pp. 383–464. <a href="https://web.archive.org/web/20171206181827/http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf">Archived</a> (PDF) from the original on 6 December 2017. Retrieved 24 September 2019.</li></ul></li></ul>
<ul><li><ul><li>Collins M, Knutti R, Arblaster J, Dufresne JL, Fichefet T, Friedlingstein P, et al. (2013). <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter12_FINAL.pdf">"Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility"</a> (PDF). IPCC AR5 WG1 2013. pp. 1029–1136. <a href="https://web.archive.org/web/20191219013928/https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter12_FINAL.pdf">Archived</a> (PDF) from the original on 19 December 2019. Retrieved 24 September 2019.</li></ul></li>
<li><a href="/facts/IPCC/sh76du1u">IPCC</a> (2018). Masson-Delmotte, V.; Zhai, P.; Pörtner, H. O.; Roberts, D.; et al. (eds.). <a href="https://www.ipcc.ch/site/assets/uploads/sites/2/2019/07/SR15_Full_Report_Low_Res.pdf">Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty</a> (PDF). Intergovernmental Panel on Climate Change. <a href="https://web.archive.org/web/20190820003425/https://www.ipcc.ch/site/assets/uploads/sites/2/2019/07/SR15_Full_Report_Low_Res.pdf">Archived</a> (PDF) from the original on 20 August 2019. Retrieved 6 March 2020.</li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://www.metoffice.gov.uk/research/climate/understanding-climate/climate-sensitivity-explained">What is 'climate sensitivity'?</a> <a href="/facts/Met_Office/V0reszST">Met Office</a></li>
<li><a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity">How scientists estimate 'climate sensitivity'</a> Carbon Brief</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">"What is 'climate sensitivity'?". Met Office. Archived from the original on 7 May 2019. Retrieved 14 February 2020. <a href="https://www.metoffice.gov.uk/research/climate/understanding-climate/climate-sensitivity-explained" target="_blank">https://www.metoffice.gov.uk/research/climate/understanding-climate/climate-sensitivity-explained</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"Climate sensitivity: fact sheet" (PDF). Australian government. Department of the Environment. Archived (PDF) from the original on 12 February 2020. Retrieved 12 February 2020. <a href="https://www.environment.gov.au/system/files/resources/d3a8654f-e1f1-4d3f-85a1-4c2d5f354047/files/factsheetclimatesensitivitycsiro-bureau.pdf" target="_blank">https://www.environment.gov.au/system/files/resources/d3a8654f-e1f1-4d3f-85a1-4c2d5f354047/files/factsheetclimatesensitivitycsiro-bureau.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022. <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf" target="_blank">https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Tanaka K, O'Neill BC (2018). "The Paris Agreement zero-emissions goal is not always consistent with the 1.5 °C and 2 °C temperature targets". Nature Climate Change. 8 (4): 319–324. Bibcode:2018NatCC...8..319T. doi:10.1038/s41558-018-0097-x. ISSN 1758-6798. S2CID 91163896. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">PALAEOSENS Project Members (November 2012). "Making sense of palaeoclimate sensitivity" (PDF). Nature. 491 (7426): 683–691. Bibcode:2012Natur.491..683P. doi:10.1038/nature11574. hdl:2078.1/118863. PMID 23192145. S2CID 2840337. Archived (PDF) from the original on 15 August 2017. Retrieved 24 September 2013. <a href="http://academiccommons.columbia.edu/download/fedora_content/download/ac:162782/CONTENT/Paleosens_Project_Members_2012.pdf" target="_blank">http://academiccommons.columbia.edu/download/fedora_content/download/ac:162782/CONTENT/Paleosens_Project_Members_2012.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Climate Change: The IPCC Scientific Assessment (1990), Report prepared for Intergovernmental Panel on Climate Change by Working Group I, Houghton JT, Jenkins GT, Ephraums JJ (eds.), chapter 2, Radiative Forcing of Climate Archived 2018-08-08 at the Wayback Machine, pp. 41–68 <a href="https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_02.pdf" target="_blank">https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_02.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">National Research Council (2005). Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties. The National Academic Press. doi:10.17226/11175. ISBN 978-0-309-09506-8. <a href="978-0-309-09506-8" target="_blank">978-0-309-09506-8</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Butler J. and Montzka S. (2020). "The NOAA Annual Greenhouse Gas Index (AGGI)". NOAA Global Monitoring Laboratory/Earth System Research Laboratories. <a href="https://www.esrl.noaa.gov/gmd/aggi/aggi.html" target="_blank">https://www.esrl.noaa.gov/gmd/aggi/aggi.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">"Direct observations confirm that humans are throwing Earth's energy budget off balance". phys.org. 26 March 2021. <a href="https://phys.org/news/2021-03-humans-earth-energy.html" target="_blank">https://phys.org/news/2021-03-humans-earth-energy.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Feldman, D.R., W.D. Collins, P.J. Gero, M.S. Torn, E.J. Mlawer, and T.R. Shippert (25 February 2015). "Observational determination of surface radiative forcing by CO2 from 2000 to 2010". Nature. 519 (7543): 339–343. Bibcode:2015Natur.519..339F. doi:10.1038/nature14240. PMID 25731165. S2CID 2137527.{{cite journal}}: CS1 maint: multiple names: authors list (link) <a href="https://www.nature.com/articles/nature14240" target="_blank">https://www.nature.com/articles/nature14240</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">"Explained: Radiative forcing". MIT News. 10 March 2010. Archived from the original on 25 August 2019. Retrieved 30 March 2019. <a href="https://news.mit.edu/2010/explained-radforce-0309" target="_blank">https://news.mit.edu/2010/explained-radforce-0309</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Climate Change: The IPCC Scientific Assessment (1990), Report prepared for Intergovernmental Panel on Climate Change by Working Group I, Houghton JT, Jenkins GT, Ephraums JJ (eds.), chapter 2, Radiative Forcing of Climate Archived 2018-08-08 at the Wayback Machine, pp. 41–68 <a href="https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_02.pdf" target="_blank">https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_02.pdf</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Larson EJ, Portmann RW (12 November 2019). "Anthropogenic aerosol drives uncertainty in future climate mitigation efforts". Scientific Reports. 9 (1): 16538. Bibcode:2019NatSR...916538L. doi:10.1038/s41598-019-52901-3. ISSN 2045-2322. PMC 6851092. PMID 31719591. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851092" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851092</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Chapter 8: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf" target="_blank">https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Myhre G, Myhre CL, Forster PM, Shine KP (2017). "Halfway to doubling of CO2 radiative forcing" (PDF). Nature Geoscience. 10 (10): 710–711. Bibcode:2017NatGe..10..710M. doi:10.1038/ngeo3036. Archived (PDF) from the original on 26 April 2019. Retrieved 13 February 2020. <a href="http://centaur.reading.ac.uk/72841/1/halfwayCO2doubling_revised_v2.pdf" target="_blank">http://centaur.reading.ac.uk/72841/1/halfwayCO2doubling_revised_v2.pdf</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">The CO2 level in 2016 was 403 ppm, which is less than 50% higher than the pre-industrial CO2 concentration of 278 ppm. However, because increased concentrations have a progressively-smaller warming effect, the Earth was already more than halfway to doubling of radiative forcing caused by CO2. <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Watts J (8 October 2018). "We have 12 years to limit climate change catastrophe, warns UN". The Guardian. ISSN 0261-3077. Archived from the original on 11 August 2019. Retrieved 13 February 2020. <a href="https://www.theguardian.com/environment/2018/oct/08/global-warming-must-not-exceed-15c-warns-landmark-un-report" target="_blank">https://www.theguardian.com/environment/2018/oct/08/global-warming-must-not-exceed-15c-warns-landmark-un-report</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">Hope C (November 2015). "The $10 trillion value of better information about the transient climate response". Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences. 373 (2054): 20140429. Bibcode:2015RSPTA.37340429H. doi:10.1098/rsta.2014.0429. PMID 26438286. <a href="https://doi.org/10.1098%2Frsta.2014.0429" target="_blank">https://doi.org/10.1098%2Frsta.2014.0429</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">Freeman MC, Wagner G, Zeckhauser RJ (November 2015). "Climate sensitivity uncertainty: when is good news bad?" (PDF). Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences. 373 (2055): 20150092. Bibcode:2015RSPTA.37350092F. doi:10.1098/rsta.2015.0092. PMID 26460117. S2CID 13843499. Archived (PDF) from the original on 22 February 2020. Retrieved 22 February 2020. <a href="http://eprints.whiterose.ac.uk/111971/1/For_repository.pdf" target="_blank">http://eprints.whiterose.ac.uk/111971/1/For_repository.pdf</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Tanaka K, O'Neill BC (2018). "The Paris Agreement zero-emissions goal is not always consistent with the 1.5 °C and 2 °C temperature targets". Nature Climate Change. 8 (4): 319–324. Bibcode:2018NatCC...8..319T. doi:10.1038/s41558-018-0097-x. ISSN 1758-6798. S2CID 91163896. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">Dyke J (24 July 2019). "Opinion: Europe is burning just as scientists offer a chilling truth about climate change". The Independent. Archived from the original on 25 July 2019. Retrieved 26 July 2019. <a href="https://www.independent.co.uk/voices/europe-heatwave-climate-change-europe-global-warming-science-a9018426.html" target="_blank">https://www.independent.co.uk/voices/europe-heatwave-climate-change-europe-global-warming-science-a9018426.html</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">Nijsse FJ, Cox PM, Huntingford C, Williamson MS (2019). "Decadal global temperature variability increases strongly with climate sensitivity" (PDF). Nature Climate Change. 9 (8): 598–601. Bibcode:2019NatCC...9..598N. doi:10.1038/s41558-019-0527-4. ISSN 1758-6798. S2CID 198914522. Archived (PDF) from the original on 6 May 2020. Retrieved 8 March 2020. <a href="http://nora.nerc.ac.uk/id/eprint/524582/1/N524582PP.pdf" target="_blank">http://nora.nerc.ac.uk/id/eprint/524582/1/N524582PP.pdf</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">The calculation is as follows. In equilibrium, the energy of incoming and outgoing radiation have to balance. The outgoing radiation 
 
 
 
 F
 
 
 {\displaystyle F}
 
 is given by the Stefan–Boltzmann law: 
 
 
 
 F
 =
 −
 σ
 
 T
 
 4
 
 
 
 
 {\displaystyle F=-\sigma T^{4}}
 
. When incoming radiation increases, the outgoing radiation and therefore temperature must increase as well. The temperature rise 
 
 
 
 Δ
 
 T
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 
 
 {\displaystyle \Delta T_{2\times CO_{2}}}
 
 directly caused by the additional radiative forcing, 
 
 
 
 Δ
 
 F
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 
 
 {\displaystyle \Delta F_{2\times CO_{2}}}
 
 because of the doubling of CO2 is then given by

Δ
 
 F
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 =
 
 
 
 d
 F
 
 
 d
 T
 
 
 
 Δ
 
 T
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 =
 4
 σ
 
 T
 
 3
 
 
 Δ
 
 T
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 
 
 {\displaystyle \Delta F_{2\times CO_{2}}={\frac {dF}{dT}}\Delta T_{2\times CO_{2}}=4\sigma T^{3}\Delta T_{2\times CO_{2}}}
 
.
Given an effective temperature of 255 K (−18 °C; −1 °F), a constant lapse rate, the value of the Stefan–Boltzmann constant 
 
 
 
 σ
 
 
 {\displaystyle \sigma }
 
 of 5.67 
 
 
 
 ×
 
 10
 
 −
 8
 
 
 
 
 {\displaystyle \times 10^{-8}}
 
W/m2 K−4 and 
 
 
 
 Δ
 
 F
 
 2
 ×
 C
 
 O
 
 2
 
 
 
 
 
 
 {\displaystyle \Delta F_{2\times CO_{2}}}
 
around 4 W/m2, the equation gives a climate sensitivity of a world without feedback of approximately 1 K. <a href="/wiki/Stefan%E2%80%93Boltzmann_law" target="_blank">/wiki/Stefan%E2%80%93Boltzmann_law</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">Roe G (2009). "Feedbacks, Timescales, and Seeing Red". Annual Review of Earth and Planetary Sciences. 37 (1): 93–115. Bibcode:2009AREPS..37...93R. doi:10.1146/annurev.earth.061008.134734. S2CID 66109238. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">Rahmstorf S (2008). "Anthropogenic Climate Change: Revisiting the Facts" (PDF). In Zedillo E (ed.). Global Warming: Looking Beyond Kyoto. Brookings Institution Press. pp. 34–53. Archived (PDF) from the original on 14 July 2019. Retrieved 14 August 2008. <a href="/wiki/Stefan_Rahmstorf" target="_blank">/wiki/Stefan_Rahmstorf</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
<li id="fn:26">Lenton TM, Rockström J, Gaffney O, Rahmstorf S, Richardson K, Steffen W, Schellnhuber HJ (November 2019). "Climate tipping points - too risky to bet against". Nature. 575 (7784): 592–595. Bibcode:2019Natur.575..592L. doi:10.1038/d41586-019-03595-0. hdl:10871/40141. PMID 31776487. <a href="https://doi.org/10.1038%2Fd41586-019-03595-0" target="_blank">https://doi.org/10.1038%2Fd41586-019-03595-0</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></li>
<li id="fn:27">Armstrong McKay, David I.; Staal, Arie; Abrams, Jesse F.; Winkelmann, Ricarda; Sakschewski, Boris; Loriani, Sina; Fetzer, Ingo; Cornell, Sarah E.; Rockström, Johan; Lenton, Timothy M. (9 September 2022). "Exceeding 1.5°C global warming could trigger multiple climate tipping points". Science. 377 (6611): eabn7950. doi:10.1126/science.abn7950. hdl:10871/131584. ISSN 0036-8075. PMID 36074831. S2CID 252161375. <a href="https://www.science.org/doi/10.1126/science.abn7950" target="_blank">https://www.science.org/doi/10.1126/science.abn7950</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></li>
<li id="fn:28">Rahmstorf S (2008). "Anthropogenic Climate Change: Revisiting the Facts" (PDF). In Zedillo E (ed.). Global Warming: Looking Beyond Kyoto. Brookings Institution Press. pp. 34–53. Archived (PDF) from the original on 14 July 2019. Retrieved 14 August 2008. <a href="/wiki/Stefan_Rahmstorf" target="_blank">/wiki/Stefan_Rahmstorf</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">Roe G (2009). "Feedbacks, Timescales, and Seeing Red". Annual Review of Earth and Planetary Sciences. 37 (1): 93–115. Bibcode:2009AREPS..37...93R. doi:10.1146/annurev.earth.061008.134734. S2CID 66109238. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">Gregory, J. M.; Andrews, T. (2016). "Variation in climate sensitivity and feedback parameters during the historical period". Geophysical Research Letters. 43 (8): 3911–3920. Bibcode:2016GeoRL..43.3911G. doi:10.1002/2016GL068406. ISSN 1944-8007. <a href="https://doi.org/10.1002%2F2016GL068406" target="_blank">https://doi.org/10.1002%2F2016GL068406</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
<li id="fn:31">Hausfather Z (19 June 2018). "Explainer: How scientists estimate climate sensitivity". Carbon Brief. Archived from the original on 1 April 2020. Retrieved 14 March 2019. <a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity" target="_blank">https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity</a> <a href="#fnref:31" class="footnote-back-ref">↩</a></li>
<li id="fn:32">Here, the IPCC definition is used. In some other sources, the climate sensitivity parameter is simply called the climate sensitivity. The inverse of this parameter, is called the climate feedback parameter and is expressed in (W/m2)/°C. <a href="#fnref:32" class="footnote-back-ref">↩</a></li>
<li id="fn:33">Modak A, Bala G, Cao L, Caldeira K (2016). "Why must a solar forcing be larger than a CO2forcing to cause the same global mean surface temperature change?" (PDF). Environmental Research Letters. 11 (4): 044013. Bibcode:2016ERL....11d4013M. doi:10.1088/1748-9326/11/4/044013. Archived (PDF) from the original on 13 July 2021. Retrieved 22 February 2020. <a href="http://eprints.iisc.ac.in/53977/1/Env_Res_Let_11-4_044013_2016.pdf" target="_blank">http://eprints.iisc.ac.in/53977/1/Env_Res_Let_11-4_044013_2016.pdf</a> <a href="#fnref:33" class="footnote-back-ref">↩</a></li>
<li id="fn:34">Planton S (2013). "Annex III: Glossary" (PDF). In Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, Midgley PM (eds.). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. p. 1451. Archived (PDF) from the original on 16 October 2021. Retrieved 30 April 2019. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf</a> <a href="#fnref:34" class="footnote-back-ref">↩</a></li>
<li id="fn:35">Randall DA, et al. (2007). "8.6.2 Interpreting the Range of Climate Sensitivity Estimates Among General Circulation Models, In: Climate Models and Their Evaluation.". In Solomon SD, et al. (eds.). Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. Archived from the original on 30 June 2018. Retrieved 1 July 2018. <a href="https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-6-2.html" target="_blank">https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-6-2.html</a> <a href="#fnref:35" class="footnote-back-ref">↩</a></li>
<li id="fn:36">Hansen J, Sato M, Kharecha P, von Schuckmann K (2011). "Earth's energy imbalance and implications". Atmospheric Chemistry and Physics. 11 (24): 13421–13449. arXiv:1105.1140. Bibcode:2011ACP....1113421H. doi:10.5194/acp-11-13421-2011. S2CID 16937940. <a href="https://doi.org/10.5194%2Facp-11-13421-2011" target="_blank">https://doi.org/10.5194%2Facp-11-13421-2011</a> <a href="#fnref:36" class="footnote-back-ref">↩</a></li>
<li id="fn:37">Collins et al. 2013, Executive Summary; p. 1033 - Collins M, Knutti R, Arblaster J, Dufresne JL, Fichefet T, Friedlingstein P, et al. (2013). "Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility" (PDF). IPCC AR5 WG1 2013. pp. 1029–1136. Archived (PDF) from the original on 19 December 2019. Retrieved 24 September 2019. <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter12_FINAL.pdf" target="_blank">https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter12_FINAL.pdf</a> <a href="#fnref:37" class="footnote-back-ref">↩</a></li>
<li id="fn:38">Millar, Richard J.; Friedlingstein, Pierre (13 May 2018). "The utility of the historical record for assessing the transient climate response to cumulative emissions". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 376 (2119): 20160449. Bibcode:2018RSPTA.37660449M. doi:10.1098/rsta.2016.0449. PMC 5897822. PMID 29610381. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5897822" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5897822</a> <a href="#fnref:38" class="footnote-back-ref">↩</a></li>
<li id="fn:39">Matthews HD, Gillett NP, Stott PA, Zickfeld K (June 2009). "The proportionality of global warming to cumulative carbon emissions". Nature. 459 (7248): 829–832. Bibcode:2009Natur.459..829M. doi:10.1038/nature08047. PMID 19516338. S2CID 4423773. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:39" class="footnote-back-ref">↩</a></li>
<li id="fn:40">Hausfather Z (19 June 2018). "Explainer: How scientists estimate climate sensitivity". Carbon Brief. Archived from the original on 1 April 2020. Retrieved 14 March 2019. <a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity" target="_blank">https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity</a> <a href="#fnref:40" class="footnote-back-ref">↩</a></li>
<li id="fn:41">IPCC (2018). "Annex I: Glossary" (PDF). IPCC SR15 2018. Archived (PDF) from the original on 19 August 2019. Retrieved 6 March 2020. <a href="/wiki/IPCC" target="_blank">/wiki/IPCC</a> <a href="#fnref:41" class="footnote-back-ref">↩</a></li>
<li id="fn:42">Gregory JM, Ingram WJ, Palmer MA, Jones GS, Stott PA, Thorpe RB, Lowe JA, Johns TC, Williams KD (2004). "A new method for diagnosing radiative forcing and climate sensitivity". Geophysical Research Letters. 31 (3): L03205. Bibcode:2004GeoRL..31.3205G. doi:10.1029/2003GL018747. S2CID 73672483. <a href="https://doi.org/10.1029%2F2003GL018747" target="_blank">https://doi.org/10.1029%2F2003GL018747</a> <a href="#fnref:42" class="footnote-back-ref">↩</a></li>
<li id="fn:43">"Archived copy" (PDF). Archived (PDF) from the original on 11 August 2021. Retrieved 13 August 2021.{{cite web}}: CS1 maint: archived copy as title (link) <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf" target="_blank">https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf</a> <a href="#fnref:43" class="footnote-back-ref">↩</a></li>
<li id="fn:44">Hawkins, Ed; Forster, Piers (2019). "Climate sensitivity: how much warming results from increases in atmospheric carbon dioxide (CO2)?". Weather. 74 (4): 134. Bibcode:2019Wthr...74..134H. doi:10.1002/wea.3400. ISSN 1477-8696. <a href="https://doi.org/10.1002%2Fwea.3400" target="_blank">https://doi.org/10.1002%2Fwea.3400</a> <a href="#fnref:44" class="footnote-back-ref">↩</a></li>
<li id="fn:45">Planton S (2013). "Annex III: Glossary" (PDF). In Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, Midgley PM (eds.). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. p. 1451. Archived (PDF) from the original on 16 October 2021. Retrieved 30 April 2019. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf</a> <a href="#fnref:45" class="footnote-back-ref">↩</a></li>
<li id="fn:46">Bitz CM, Shell KM, Gent PR, Bailey DA, Danabasoglu G, Armour KC, et al. (2011). "Climate Sensitivity of the Community Climate System Model, Version 4" (PDF). Journal of Climate. 25 (9): 3053–3070. CiteSeerX 10.1.1.716.6228. doi:10.1175/JCLI-D-11-00290.1. ISSN 0894-8755. S2CID 7843257. Archived (PDF) from the original on 8 August 2017. Retrieved 22 February 2020. <a href="http://www.atmos.washington.edu/~bitz/CCSM4_climsens_preprint.pdf" target="_blank">http://www.atmos.washington.edu/~bitz/CCSM4_climsens_preprint.pdf</a> <a href="#fnref:46" class="footnote-back-ref">↩</a></li>
<li id="fn:47">Prentice IC, et al. (2001). "9.2.1 Climate Forcing and Climate Response, in chapter 9. Projections of Future Climate Change" (PDF). In Houghton JT, et al. (eds.). Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. ISBN 9780521807678. <a href="9780521807678" target="_blank">9780521807678</a> <a href="#fnref:47" class="footnote-back-ref">↩</a></li>
<li id="fn:48">Planton S (2013). "Annex III: Glossary" (PDF). In Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, Midgley PM (eds.). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. p. 1451. Archived (PDF) from the original on 16 October 2021. Retrieved 30 April 2019. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_AnnexIII_FINAL.pdf</a> <a href="#fnref:48" class="footnote-back-ref">↩</a></li>
<li id="fn:49">Rugenstein, Maria; Bloch-Johnson, Jonah; Gregory, Jonathan; Andrews, Timothy; Mauritsen, Thorsten; Li, Chao; Frölicher, Thomas L.; Paynter, David; Danabasoglu, Gokhan; Yang, Shuting; Dufresne, Jean-Louis (2020). "Equilibrium Climate Sensitivity Estimated by Equilibrating Climate Models" (PDF). Geophysical Research Letters. 47 (4): e2019GL083898. Bibcode:2020GeoRL..4783898R. doi:10.1029/2019GL083898. ISSN 1944-8007. Archived (PDF) from the original on 30 August 2020. Retrieved 18 September 2020. <a href="http://centaur.reading.ac.uk/87462/1/rugenstein19ecs_authors.pdf" target="_blank">http://centaur.reading.ac.uk/87462/1/rugenstein19ecs_authors.pdf</a> <a href="#fnref:49" class="footnote-back-ref">↩</a></li>
<li id="fn:50">Knutti R, Rugenstein MA, Knutti R (2017). "Beyond equilibrium climate sensitivity". Nature Geoscience. 10 (10): 727–736. Bibcode:2017NatGe..10..727K. doi:10.1038/ngeo3017. hdl:20.500.11850/197761. ISSN 1752-0908. S2CID 134579878. <a href="https://www.research.ed.ac.uk/en/publications/6a35b333-b70d-4cc1-aa5c-3c68ba070fae" target="_blank">https://www.research.ed.ac.uk/en/publications/6a35b333-b70d-4cc1-aa5c-3c68ba070fae</a> <a href="#fnref:50" class="footnote-back-ref">↩</a></li>
<li id="fn:51">Previdi M, Liepert BG, Peteet D, Hansen J, Beerling DJ, Broccoli AJ, et al. (2013). "Climate sensitivity in the Anthropocene". Quarterly Journal of the Royal Meteorological Society. 139 (674): 1121–1131. Bibcode:2013QJRMS.139.1121P. CiteSeerX 10.1.1.434.854. doi:10.1002/qj.2165. <a href="https://doi.org/10.1002%2Fqj.2165" target="_blank">https://doi.org/10.1002%2Fqj.2165</a> <a href="#fnref:51" class="footnote-back-ref">↩</a></li>
<li id="fn:52">Feng, Ran; Bette L., Otto-Bliesner; Brady, Esther C.; Rosenbloom, Nan A. (4 January 2020). "Increasing Earth System Sensitivity in mid-Pliocene simulations from CCSM4 to CESM2". Ess Open Archive ePrints. 105. Bibcode:2020esoar.10501546F. doi:10.1002/essoar.10501546.1. <a href="/wiki/Bette_Otto-Bliesner" target="_blank">/wiki/Bette_Otto-Bliesner</a> <a href="#fnref:52" class="footnote-back-ref">↩</a></li>
<li id="fn:53">"Target CO2". RealClimate. 7 April 2008. Archived from the original on 24 August 2017. <a href="http://www.realclimate.org/index.php/archives/2008/04/target-co2/" target="_blank">http://www.realclimate.org/index.php/archives/2008/04/target-co2/</a> <a href="#fnref:53" class="footnote-back-ref">↩</a></li>
<li id="fn:54">"On sensitivity: Part I". RealClimate.org. 3 January 2013. Archived from the original on 30 July 2018. Retrieved 30 July 2018. <a href="http://www.realclimate.org/index.php/archives/2013/01/on-sensitivity-part-i/" target="_blank">http://www.realclimate.org/index.php/archives/2013/01/on-sensitivity-part-i/</a> <a href="#fnref:54" class="footnote-back-ref">↩</a></li>
<li id="fn:55">Marvel K, Schmidt GA, Miller RL, Nazarenko LS (2016). "Implications for climate sensitivity from the response to individual forcings". Nature Climate Change. 6 (4): 386–389. Bibcode:2016NatCC...6..386M. doi:10.1038/nclimate2888. hdl:2060/20160012693. ISSN 1758-6798. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:55" class="footnote-back-ref">↩</a></li>
<li id="fn:56">Pincus R, Mauritsen T (2017). "Committed warming inferred from observations". Nature Climate Change. 7 (9): 652–655. Bibcode:2017NatCC...7..652M. doi:10.1038/nclimate3357. hdl:11858/00-001M-0000-002D-CBC9-F. ISSN 1758-6798. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:56" class="footnote-back-ref">↩</a></li>
<li id="fn:57">Pfister PL, Stocker TF (2017). "State-Dependence of the Climate Sensitivity in Earth System Models of Intermediate Complexity" (PDF). Geophysical Research Letters. 44 (20): 10643–10653. Bibcode:2017GeoRL..4410643P. doi:10.1002/2017GL075457. ISSN 1944-8007. Archived (PDF) from the original on 22 February 2020. Retrieved 22 February 2020. <a href="https://boris.unibe.ch/112659/1/Pfister_et_al-2017-Geophysical_Research_Letters.pdf" target="_blank">https://boris.unibe.ch/112659/1/Pfister_et_al-2017-Geophysical_Research_Letters.pdf</a> <a href="#fnref:57" class="footnote-back-ref">↩</a></li>
<li id="fn:58">Hansen J, Sato M, Russell G, Kharecha P (October 2013). "Climate sensitivity, sea level and atmospheric carbon dioxide". Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences. 371 (2001): 20120294. arXiv:1211.4846. Bibcode:2013RSPTA.37120294H. doi:10.1098/rsta.2012.0294. PMC 3785813. PMID 24043864. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785813" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785813</a> <a href="#fnref:58" class="footnote-back-ref">↩</a></li>
<li id="fn:59">Hansen, James; Sato, Makiko; Russell, Gary; Kharecha, Pushker (28 October 2013). "Climate sensitivity, sea level and atmospheric carbon dioxide". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 371 (2001): 20120294. arXiv:1211.4846. Bibcode:2013RSPTA.37120294H. doi:10.1098/rsta.2012.0294. PMC 3785813. PMID 24043864. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785813" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785813</a> <a href="#fnref:59" class="footnote-back-ref">↩</a></li>
<li id="fn:60">Lontzek TS, Lenton TM, Cai Y (2016). "Risk of multiple interacting tipping points should encourage rapid CO2 emission reduction". Nature Climate Change. 6 (5): 520–525. Bibcode:2016NatCC...6..520C. doi:10.1038/nclimate2964. hdl:10871/20598. ISSN 1758-6798. S2CID 38156745. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:60" class="footnote-back-ref">↩</a></li>
<li id="fn:61">Pfister PL, Stocker TF (2017). "State-Dependence of the Climate Sensitivity in Earth System Models of Intermediate Complexity" (PDF). Geophysical Research Letters. 44 (20): 10643–10653. Bibcode:2017GeoRL..4410643P. doi:10.1002/2017GL075457. ISSN 1944-8007. Archived (PDF) from the original on 22 February 2020. Retrieved 22 February 2020. <a href="https://boris.unibe.ch/112659/1/Pfister_et_al-2017-Geophysical_Research_Letters.pdf" target="_blank">https://boris.unibe.ch/112659/1/Pfister_et_al-2017-Geophysical_Research_Letters.pdf</a> <a href="#fnref:61" class="footnote-back-ref">↩</a></li>
<li id="fn:62">Skeie RB, Berntsen T, Aldrin M, Holden M, Myhre G (2014). "A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series". Earth System Dynamics. 5 (1): 139–175. Bibcode:2014ESD.....5..139S. doi:10.5194/esd-5-139-2014. S2CID 55652873. <a href="https://doi.org/10.5194%2Fesd-5-139-2014" target="_blank">https://doi.org/10.5194%2Fesd-5-139-2014</a> <a href="#fnref:62" class="footnote-back-ref">↩</a></li>
<li id="fn:63">Armour KC (2017). "Energy budget constraints on climate sensitivity in light of inconstant climate feedbacks". Nature Climate Change. 7 (5): 331–335. Bibcode:2017NatCC...7..331A. doi:10.1038/nclimate3278. ISSN 1758-6798. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:63" class="footnote-back-ref">↩</a></li>
<li id="fn:64">Skeie RB, Berntsen T, Aldrin M, Holden M, Myhre G (2014). "A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series". Earth System Dynamics. 5 (1): 139–175. Bibcode:2014ESD.....5..139S. doi:10.5194/esd-5-139-2014. S2CID 55652873. <a href="https://doi.org/10.5194%2Fesd-5-139-2014" target="_blank">https://doi.org/10.5194%2Fesd-5-139-2014</a> <a href="#fnref:64" class="footnote-back-ref">↩</a></li>
<li id="fn:65">Forster PM, Gregory JM (2006). "The Climate Sensitivity and Its Components Diagnosed from Earth Radiation Budget Data". Journal of Climate. 19 (1): 39–52. Bibcode:2006JCli...19...39F. doi:10.1175/JCLI3611.1. Archived from the original on 17 July 2019. Retrieved 17 July 2019. <a href="/wiki/Piers_Forster" target="_blank">/wiki/Piers_Forster</a> <a href="#fnref:65" class="footnote-back-ref">↩</a></li>
<li id="fn:66">Lewis N, Curry JA (2014). "The implications for climate sensitivity of AR5 forcing and heat uptake estimates". Climate Dynamics. 45 (3–4): 1009–1023. Bibcode:2015ClDy...45.1009L. doi:10.1007/s00382-014-2342-y. S2CID 55828449. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:66" class="footnote-back-ref">↩</a></li>
<li id="fn:67">Otto A, Otto FE, Boucher O, Church J, Hegerl G, Forster PM, et al. (2013). "Energy budget constraints on climate response" (PDF). Nature Geoscience. 6 (6): 415–416. Bibcode:2013NatGe...6..415O. doi:10.1038/ngeo1836. ISSN 1752-0908. Archived (PDF) from the original on 26 September 2019. Retrieved 4 December 2019. <a href="http://eprints.whiterose.ac.uk/76064/7/ngeo1836%281%29_with_coversheet.pdf" target="_blank">http://eprints.whiterose.ac.uk/76064/7/ngeo1836%281%29_with_coversheet.pdf</a> <a href="#fnref:67" class="footnote-back-ref">↩</a></li>
<li id="fn:68">Hausfather Z (19 June 2018). "Explainer: How scientists estimate climate sensitivity". Carbon Brief. Archived from the original on 1 April 2020. Retrieved 14 March 2019. <a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity" target="_blank">https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity</a> <a href="#fnref:68" class="footnote-back-ref">↩</a></li>
<li id="fn:69">Stolpe MB, Ed Hawkins, Cowtan K, Richardson M (2016). "Reconciled climate response estimates from climate models and the energy budget of Earth" (PDF). Nature Climate Change. 6 (10): 931–935. Bibcode:2016NatCC...6..931R. doi:10.1038/nclimate3066. ISSN 1758-6798. S2CID 89143351. Archived (PDF) from the original on 28 April 2019. Retrieved 23 September 2019. <a href="http://centaur.reading.ac.uk/65992/1/RichardsonTCR_accepted.pdf" target="_blank">http://centaur.reading.ac.uk/65992/1/RichardsonTCR_accepted.pdf</a> <a href="#fnref:69" class="footnote-back-ref">↩</a></li>
<li id="fn:70">Rahmstorf S (2008). "Anthropogenic Climate Change: Revisiting the Facts" (PDF). In Zedillo E (ed.). Global Warming: Looking Beyond Kyoto. Brookings Institution Press. pp. 34–53. Archived (PDF) from the original on 14 July 2019. Retrieved 14 August 2008. <a href="/wiki/Stefan_Rahmstorf" target="_blank">/wiki/Stefan_Rahmstorf</a> <a href="#fnref:70" class="footnote-back-ref">↩</a></li>
<li id="fn:71">Rahmstorf S (2008). "Anthropogenic Climate Change: Revisiting the Facts" (PDF). In Zedillo E (ed.). Global Warming: Looking Beyond Kyoto. Brookings Institution Press. pp. 34–53. Archived (PDF) from the original on 14 July 2019. Retrieved 14 August 2008. <a href="/wiki/Stefan_Rahmstorf" target="_blank">/wiki/Stefan_Rahmstorf</a> <a href="#fnref:71" class="footnote-back-ref">↩</a></li>
<li id="fn:72">IPCC AR5 WG1 Technical Summary 2013, p. 53-56. - Stocker TF, Qin D, Plattner GK, Alexander LV, Allen SK, Bindoff NL, et al. (2013). "Technical Summary" (PDF). IPCC AR5 WG1 2013. pp. 33–115. Archived (PDF) from the original on 20 December 2019. Retrieved 12 February 2020. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf</a> <a href="#fnref:72" class="footnote-back-ref">↩</a></li>
<li id="fn:73">IPCC AR5 WG1 Technical Summary 2013, p. 39. - Stocker TF, Qin D, Plattner GK, Alexander LV, Allen SK, Bindoff NL, et al. (2013). "Technical Summary" (PDF). IPCC AR5 WG1 2013. pp. 33–115. Archived (PDF) from the original on 20 December 2019. Retrieved 12 February 2020. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf</a> <a href="#fnref:73" class="footnote-back-ref">↩</a></li>
<li id="fn:74">Schwartz SE (2007). "Heat capacity, time constant, and sensitivity of Earth's climate system". Journal of Geophysical Research: Atmospheres. 112 (D24): D24S05. Bibcode:2007JGRD..11224S05S. CiteSeerX 10.1.1.482.4066. doi:10.1029/2007JD008746. <a href="/wiki/Stephen_E._Schwartz" target="_blank">/wiki/Stephen_E._Schwartz</a> <a href="#fnref:74" class="footnote-back-ref">↩</a></li>
<li id="fn:75">Knutti R, Kraehenmann S, Frame DJ, Allen MR (2008). "Comment on 'Heat capacity, time constant, and sensitivity of Earth's climate system' by S. E. Schwartz". Journal of Geophysical Research: Atmospheres. 113 (D15): D15103. Bibcode:2008JGRD..11315103K. doi:10.1029/2007JD009473. <a href="https://doi.org/10.1029%2F2007JD009473" target="_blank">https://doi.org/10.1029%2F2007JD009473</a> <a href="#fnref:75" class="footnote-back-ref">↩</a></li>
<li id="fn:76">Foster G, Annan JD, Schmidt GA, Mann ME (2008). "Comment on 'Heat capacity, time constant, and sensitivity of Earth's climate system' by S. E. Schwartz". Journal of Geophysical Research: Atmospheres. 113 (D15): D15102. Bibcode:2008JGRD..11315102F. doi:10.1029/2007JD009373. S2CID 17960844. <a href="https://doi.org/10.1029%2F2007JD009373" target="_blank">https://doi.org/10.1029%2F2007JD009373</a> <a href="#fnref:76" class="footnote-back-ref">↩</a></li>
<li id="fn:77">Scafetta N (2008). "Comment on 'Heat capacity, time constant, and sensitivity of Earth's climate system' by S. E. Schwartz". Journal of Geophysical Research: Atmospheres. 113 (D15): D15104. Bibcode:2008JGRD..11315104S. doi:10.1029/2007JD009586. <a href="https://doi.org/10.1029%2F2007JD009586" target="_blank">https://doi.org/10.1029%2F2007JD009586</a> <a href="#fnref:77" class="footnote-back-ref">↩</a></li>
<li id="fn:78">Tung KK, Zhou J, Camp CD (2008). "Constraining model transient climate response using independent observations of solar-cycle forcing and response" (PDF). Geophysical Research Letters. 35 (17): L17707. Bibcode:2008GeoRL..3517707T. doi:10.1029/2008GL034240. S2CID 14656629. Archived (PDF) from the original on 1 February 2017. Retrieved 1 July 2018. <a href="https://www.calpoly.edu/~camp/Publications/Tung_etal_GRL_2008.pdf" target="_blank">https://www.calpoly.edu/~camp/Publications/Tung_etal_GRL_2008.pdf</a> <a href="#fnref:78" class="footnote-back-ref">↩</a></li>
<li id="fn:79">Camp CD, Tung KK (2007). "Surface warming by the solar cycle as revealed by the composite mean difference projection". Geophysical Research Letters. 34 (14): L14703. Bibcode:2007GeoRL..3414703C. doi:10.1029/2007GL030207. <a href="https://doi.org/10.1029%2F2007GL030207" target="_blank">https://doi.org/10.1029%2F2007GL030207</a> <a href="#fnref:79" class="footnote-back-ref">↩</a></li>
<li id="fn:80">Rypdal K (2012). "Global temperature response to radiative forcing: Solar cycle versus volcanic eruptions". Journal of Geophysical Research: Atmospheres. 117 (D6). Bibcode:2012JGRD..117.6115R. doi:10.1029/2011JD017283. ISSN 2156-2202. <a href="https://doi.org/10.1029%2F2011JD017283" target="_blank">https://doi.org/10.1029%2F2011JD017283</a> <a href="#fnref:80" class="footnote-back-ref">↩</a></li>
<li id="fn:81">Merlis TM, Held IM, Stenchikov GL, Zeng F, Horowitz LW (2014). "Constraining Transient Climate Sensitivity Using Coupled Climate Model Simulations of Volcanic Eruptions". Journal of Climate. 27 (20): 7781–7795. Bibcode:2014JCli...27.7781M. doi:10.1175/JCLI-D-14-00214.1. hdl:10754/347010. ISSN 0894-8755. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:81" class="footnote-back-ref">↩</a></li>
<li id="fn:82">McSweeney R (4 February 2015). "What a three-million year fossil record tells us about climate sensitivity". Carbon Brief. Archived from the original on 31 March 2019. Retrieved 20 March 2019. <a href="https://www.carbonbrief.org/what-a-three-million-year-fossil-record-tells-us-about-climate-sensitivity" target="_blank">https://www.carbonbrief.org/what-a-three-million-year-fossil-record-tells-us-about-climate-sensitivity</a> <a href="#fnref:82" class="footnote-back-ref">↩</a></li>
<li id="fn:83">Amos, Jonathan (9 April 2019). "European team to drill for 'oldest ice'". BBC News. Archived from the original on 31 March 2020. Retrieved 4 March 2020. <a href="https://www.bbc.com/news/science-environment-47848344" target="_blank">https://www.bbc.com/news/science-environment-47848344</a> <a href="#fnref:83" class="footnote-back-ref">↩</a></li>
<li id="fn:84">Hargreaves JC, Annan JD (2009). "On the importance of paleoclimate modelling for improving predictions of future climate change" (PDF). Climate of the Past. 5 (4): 803–814. Bibcode:2009CliPa...5..803H. doi:10.5194/cp-5-803-2009. Archived (PDF) from the original on 2 December 2017. Retrieved 31 March 2019. <a href="https://www.clim-past.net/5/803/2009/cp-5-803-2009.pdf" target="_blank">https://www.clim-past.net/5/803/2009/cp-5-803-2009.pdf</a> <a href="#fnref:84" class="footnote-back-ref">↩</a></li>
<li id="fn:85">Hargreaves JC, Annan JD, Yoshimori M, Abe-Ouchi A (2012). "Can the Last Glacial Maximum constrain climate sensitivity?". Geophysical Research Letters. 39 (24): L24702. Bibcode:2012GeoRL..3924702H. doi:10.1029/2012GL053872. ISSN 1944-8007. S2CID 15222363. <a href="https://doi.org/10.1029%2F2012GL053872" target="_blank">https://doi.org/10.1029%2F2012GL053872</a> <a href="#fnref:85" class="footnote-back-ref">↩</a></li>
<li id="fn:86">Royer DL, Berner RA, Park J (March 2007). "Climate sensitivity constrained by CO2 concentrations over the past 420 million years". Nature. 446 (7135): 530–532. Bibcode:2007Natur.446..530R. doi:10.1038/nature05699. PMID 17392784. S2CID 4323367. <a href="/wiki/Dana_Royer" target="_blank">/wiki/Dana_Royer</a> <a href="#fnref:86" class="footnote-back-ref">↩</a></li>
<li id="fn:87">Kiehl JT, Shields CA (October 2013). "Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties". Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences. 371 (2001): 20130093. Bibcode:2013RSPTA.37130093K. doi:10.1098/rsta.2013.0093. PMID 24043867. <a href="https://doi.org/10.1098%2Frsta.2013.0093" target="_blank">https://doi.org/10.1098%2Frsta.2013.0093</a> <a href="#fnref:87" class="footnote-back-ref">↩</a></li>
<li id="fn:88">von der Heydt AS, Köhler P, van de Wal RS, Dijkstra HA (2014). "On the state dependency of fast feedback processes in (paleo) climate sensitivity". Geophysical Research Letters. 41 (18): 6484–6492. arXiv:1403.5391. doi:10.1002/2014GL061121. ISSN 1944-8007. S2CID 53703955. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:88" class="footnote-back-ref">↩</a></li>
<li id="fn:89">Masson-Delmotte et al. 2013 - Masson-Delmotte V, Schulz M, Abe-Ouchi A, Beer J, Ganopolski A, Rouco JG, et al. (2013). "Chapter 5: Information from Paleoclimate Archives" (PDF). IPCC AR5 WG1 2013. pp. 383–464. Archived (PDF) from the original on 6 December 2017. Retrieved 24 September 2019. <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf" target="_blank">https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf</a> <a href="#fnref:89" class="footnote-back-ref">↩</a></li>
<li id="fn:90">Hopcroft PO, Valdes PJ (2015). "How well do simulated last glacial maximum tropical temperatures constrain equilibrium climate sensitivity?: CMIP5 LGM TROPICS AND CLIMATE SENSITIVITY" (PDF). Geophysical Research Letters. 42 (13): 5533–5539. doi:10.1002/2015GL064903. Archived (PDF) from the original on 22 February 2020. Retrieved 22 February 2020. <a href="https://research-information.bris.ac.uk/files/51793503/Hopcroft_et_al_2015_Geophysical_Research_Letters.pdf" target="_blank">https://research-information.bris.ac.uk/files/51793503/Hopcroft_et_al_2015_Geophysical_Research_Letters.pdf</a> <a href="#fnref:90" class="footnote-back-ref">↩</a></li>
<li id="fn:91">Masson-Delmotte et al. 2013 - Masson-Delmotte V, Schulz M, Abe-Ouchi A, Beer J, Ganopolski A, Rouco JG, et al. (2013). "Chapter 5: Information from Paleoclimate Archives" (PDF). IPCC AR5 WG1 2013. pp. 383–464. Archived (PDF) from the original on 6 December 2017. Retrieved 24 September 2019. <a href="https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf" target="_blank">https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf</a> <a href="#fnref:91" class="footnote-back-ref">↩</a></li>
<li id="fn:92">Cooper, Vincent T. (17 April 2024). "Last Glacial Maximum pattern effects reduce climate sensitivity estimates". Science Advances. 10 (16). doi:10.1126/sciadv.adk9461. PMC 11023557. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11023557" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11023557</a> <a href="#fnref:92" class="footnote-back-ref">↩</a></li>
<li id="fn:93">Hopcroft PO, Valdes PJ (2015). "How well do simulated last glacial maximum tropical temperatures constrain equilibrium climate sensitivity?: CMIP5 LGM TROPICS AND CLIMATE SENSITIVITY" (PDF). Geophysical Research Letters. 42 (13): 5533–5539. doi:10.1002/2015GL064903. Archived (PDF) from the original on 22 February 2020. Retrieved 22 February 2020. <a href="https://research-information.bris.ac.uk/files/51793503/Hopcroft_et_al_2015_Geophysical_Research_Letters.pdf" target="_blank">https://research-information.bris.ac.uk/files/51793503/Hopcroft_et_al_2015_Geophysical_Research_Letters.pdf</a> <a href="#fnref:93" class="footnote-back-ref">↩</a></li>
<li id="fn:94">Ganopolski A, von Deimling TS (2008). "Comment on 'Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition' by Petr Chylek and Ulrike Lohmann". Geophysical Research Letters. 35 (23): L23703. Bibcode:2008GeoRL..3523703G. doi:10.1029/2008GL033888. <a href="https://doi.org/10.1029%2F2008GL033888" target="_blank">https://doi.org/10.1029%2F2008GL033888</a> <a href="#fnref:94" class="footnote-back-ref">↩</a></li>
<li id="fn:95">Schmittner A, Urban NM, Shakun JD, Mahowald NM, Clark PU, Bartlein PJ, et al. (December 2011). "Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum". Science. 334 (6061): 1385–1388. Bibcode:2011Sci...334.1385S. CiteSeerX 10.1.1.419.8341. doi:10.1126/science.1203513. PMID 22116027. S2CID 18735283. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:95" class="footnote-back-ref">↩</a></li>
<li id="fn:96">McSweeney, Robert; Hausfather, Zeke (15 January 2018). "Q&A: How do climate models work?". Carbon Brief. Archived from the original on 5 March 2019. Retrieved 7 March 2020. <a href="https://www.carbonbrief.org/qa-how-do-climate-models-work" target="_blank">https://www.carbonbrief.org/qa-how-do-climate-models-work</a> <a href="#fnref:96" class="footnote-back-ref">↩</a></li>
<li id="fn:97">Hausfather Z (19 June 2018). "Explainer: How scientists estimate climate sensitivity". Carbon Brief. Archived from the original on 1 April 2020. Retrieved 14 March 2019. <a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity" target="_blank">https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity</a> <a href="#fnref:97" class="footnote-back-ref">↩</a></li>
<li id="fn:98">Sanderson BM, Knutti R, Caldwell P (2015). "Addressing Interdependency in a Multimodel Ensemble by Interpolation of Model Properties". Journal of Climate. 28 (13): 5150–5170. Bibcode:2015JCli...28.5150S. doi:10.1175/JCLI-D-14-00361.1. ISSN 0894-8755. OSTI 1840116. S2CID 51583558. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:98" class="footnote-back-ref">↩</a></li>
<li id="fn:99">Forest CE, Stone PH, Sokolov AP, Allen MR, Webster MD (January 2002). "Quantifying uncertainties in climate system properties with the use of recent climate observations" (PDF). Science. 295 (5552): 113–117. Bibcode:2002Sci...295..113F. CiteSeerX 10.1.1.297.1145. doi:10.1126/science.1064419. PMID 11778044. S2CID 5322736. Archived (PDF) from the original on 4 June 2007. Retrieved 4 February 2006. <a href="https://dspace.mit.edu/bitstream/1721.1/3567/1/MITJPSPGC_Rpt78.pdf" target="_blank">https://dspace.mit.edu/bitstream/1721.1/3567/1/MITJPSPGC_Rpt78.pdf</a> <a href="#fnref:99" class="footnote-back-ref">↩</a></li>
<li id="fn:100">Fasullo JT, Trenberth KE (2012). "A Less Cloudy Future: The Role of Subtropical Subsidence in Climate Sensitivity". Science. 338 (6108): 792–794. Bibcode:2012Sci...338..792F. doi:10.1126/science.1227465. PMID 23139331. S2CID 2710565. Referred to by: ScienceDaily (8 November 2012). "Future warming likely to be on high side of climate projections, analysis finds". ScienceDaily. Archived from the original on 1 July 2018. Retrieved 9 March 2018. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:100" class="footnote-back-ref">↩</a></li>
<li id="fn:101">Brown PT, Caldeira K (December 2017). "Greater future global warming inferred from Earth's recent energy budget". Nature. 552 (7683): 45–50. Bibcode:2017Natur.552...45B. doi:10.1038/nature24672. PMID 29219964. S2CID 602036. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:101" class="footnote-back-ref">↩</a></li>
<li id="fn:102">Cox PM, Huntingford C, Williamson MS (January 2018). "Emergent constraint on equilibrium climate sensitivity from global temperature variability" (PDF). Nature. 553 (7688): 319–322. Bibcode:2018Natur.553..319C. doi:10.1038/nature25450. hdl:10871/34396. PMID 29345639. S2CID 205263680. Archived (PDF) from the original on 29 August 2019. Retrieved 17 July 2019. <a href="http://nora.nerc.ac.uk/id/eprint/519612/1/N519612PP.pdf" target="_blank">http://nora.nerc.ac.uk/id/eprint/519612/1/N519612PP.pdf</a> <a href="#fnref:102" class="footnote-back-ref">↩</a></li>
<li id="fn:103">Brown PT, Stolpe MB, Caldeira K (November 2018). "Assumptions for emergent constraints". Nature. 563 (7729): E1 – E3. Bibcode:2018Natur.563E...1B. doi:10.1038/s41586-018-0638-5. PMID 30382203. S2CID 53190363. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:103" class="footnote-back-ref">↩</a></li>
<li id="fn:104">Cox PM, Williamson MS, Nijsse FJ, Huntingford C (November 2018). "Cox et al. reply". Nature. 563 (7729): E10 – E15. Bibcode:2018Natur.563E..10C. doi:10.1038/s41586-018-0641-x. PMID 30382204. S2CID 53145737. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:104" class="footnote-back-ref">↩</a></li>
<li id="fn:105">Caldwell PM, Zelinka MD, Klein SA (2018). "Evaluating Emergent Constraints on Equilibrium Climate Sensitivity". Journal of Climate. 31 (10): 3921–3942. Bibcode:2018JCli...31.3921C. doi:10.1175/JCLI-D-17-0631.1. ISSN 0894-8755. OSTI 1438763. <a href="https://doi.org/10.1175%2FJCLI-D-17-0631.1" target="_blank">https://doi.org/10.1175%2FJCLI-D-17-0631.1</a> <a href="#fnref:105" class="footnote-back-ref">↩</a></li>
<li id="fn:106">"CMIP - History". pcmdi.llnl.gov. Program for Climate Model Diagnosis & Intercomparison. Archived from the original on 28 July 2020. Retrieved 6 March 2020. <a href="https://pcmdi.llnl.gov/mips/cmip5/history.html" target="_blank">https://pcmdi.llnl.gov/mips/cmip5/history.html</a> <a href="#fnref:106" class="footnote-back-ref">↩</a></li>
<li id="fn:107">Lapenis AG (1998). "Arrhenius and the Intergovernmental Panel on Climate Change". Eos, Transactions American Geophysical Union. 79 (23): 271. Bibcode:1998EOSTr..79..271L. doi:10.1029/98EO00206. ISSN 2324-9250. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:107" class="footnote-back-ref">↩</a></li>
<li id="fn:108">Sample I (30 June 2005). "The father of climate change". The Guardian. ISSN 0261-3077. Retrieved 18 March 2019. <a href="https://www.theguardian.com/environment/2005/jun/30/climatechange.climatechangeenvironment2" target="_blank">https://www.theguardian.com/environment/2005/jun/30/climatechange.climatechangeenvironment2</a> <a href="#fnref:108" class="footnote-back-ref">↩</a></li>
<li id="fn:109">Anderson TR, Hawkins E, Jones PD (September 2016). "2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today's Earth System Models" (PDF). Endeavour. 40 (3): 178–187. doi:10.1016/j.endeavour.2016.07.002. PMID 27469427. Archived (PDF) from the original on 19 August 2019. Retrieved 22 February 2020. <a href="http://centaur.reading.ac.uk/66238/1/anderson_etal_2016_Callendar.pdf" target="_blank">http://centaur.reading.ac.uk/66238/1/anderson_etal_2016_Callendar.pdf</a> <a href="#fnref:109" class="footnote-back-ref">↩</a></li>
<li id="fn:110">Manabe S, Wetherald RT (May 1967). "Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity". Journal of the Atmospheric Sciences. 24 (3): 241–259. Bibcode:1967JAtS...24..241M. doi:10.1175/1520-0469(1967)024<0241:teotaw>2.0.co;2. S2CID 124082372. <a href="https://doi.org/10.1175%2F1520-0469%281967%29024%3C0241%3Ateotaw%3E2.0.co%3B2" target="_blank">https://doi.org/10.1175%2F1520-0469%281967%29024%3C0241%3Ateotaw%3E2.0.co%3B2</a> <a href="#fnref:110" class="footnote-back-ref">↩</a></li>
<li id="fn:111">Forster P (May 2017). "In Retrospect: Half a century of robust climate models" (PDF). Nature. 545 (7654): 296–297. Bibcode:2017Natur.545..296F. doi:10.1038/545296a. PMID 28516918. S2CID 205094044. Archived (PDF) from the original on 19 October 2019. Retrieved 19 October 2019. <a href="https://aos.princeton.edu/sites/aos/files/manabewetherald_retro-1.pdf" target="_blank">https://aos.princeton.edu/sites/aos/files/manabewetherald_retro-1.pdf</a> <a href="#fnref:111" class="footnote-back-ref">↩</a></li>
<li id="fn:112">Pidcock R (6 July 2015). "The most influential climate change papers of all time". CarbonBrief. Archived from the original on 19 October 2019. Retrieved 19 October 2019. <a href="https://www.carbonbrief.org/the-most-influential-climate-change-papers-of-all-time" target="_blank">https://www.carbonbrief.org/the-most-influential-climate-change-papers-of-all-time</a> <a href="#fnref:112" class="footnote-back-ref">↩</a></li>
<li id="fn:113">Ad Hoc Study Group on Carbon Dioxide and Climate (1979). Carbon Dioxide and Climate: A Scientific Assessment (PDF). National Academy of Sciences. doi:10.17226/12181. ISBN 978-0-309-11910-8. Archived from the original (PDF) on 13 August 2011.
 <a href="978-0-309-11910-8" target="_blank">978-0-309-11910-8</a> <a href="#fnref:113" class="footnote-back-ref">↩</a></li>
<li id="fn:114">Kerr RA (August 2004). "Climate change. Three degrees of consensus". Science. 305 (5686): 932–934. doi:10.1126/science.305.5686.932. PMID 15310873. S2CID 129548731. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:114" class="footnote-back-ref">↩</a></li>
<li id="fn:115">Rahmstorf S (2008). "Anthropogenic Climate Change: Revisiting the Facts" (PDF). In Zedillo E (ed.). Global Warming: Looking Beyond Kyoto. Brookings Institution Press. pp. 34–53. Archived (PDF) from the original on 14 July 2019. Retrieved 14 August 2008. <a href="/wiki/Stefan_Rahmstorf" target="_blank">/wiki/Stefan_Rahmstorf</a> <a href="#fnref:115" class="footnote-back-ref">↩</a></li>
<li id="fn:116">Forster PM (2016). "Inference of Climate Sensitivity from Analysis of Earth's Energy Budget". Annual Review of Earth and Planetary Sciences. 44 (1): 85–106. Bibcode:2016AREPS..44...85F. doi:10.1146/annurev-earth-060614-105156. <a href="https://doi.org/10.1146%2Fannurev-earth-060614-105156" target="_blank">https://doi.org/10.1146%2Fannurev-earth-060614-105156</a> <a href="#fnref:116" class="footnote-back-ref">↩</a></li>
<li id="fn:117">Climate Change: The IPCC Scientific Assessment (1990), Report prepared for Intergovernmental Panel on Climate Change by Working Group I, Houghton JT, Jenkins GJ, Ephraums JJ (eds.), chapter 5, Equilibrium Climate Change — and its Implications for the Future Archived 2018-04-13 at the Wayback Machine, pp. 138–139 <a href="https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_05.pdf" target="_blank">https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_05.pdf</a> <a href="#fnref:117" class="footnote-back-ref">↩</a></li>
<li id="fn:118">IPCC '92 p. 118 section B3.5 <a href="#fnref:118" class="footnote-back-ref">↩</a></li>
<li id="fn:119">IPCC SAR p. 34, technical summary section D.2 <a href="#fnref:119" class="footnote-back-ref">↩</a></li>
<li id="fn:120">Albritton DL, et al. (2001). "Technical Summary: F.3 Projections of Future Changes in Temperature". In Houghton JT, et al. (eds.). Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. Archived from the original on 12 January 2012. <a href="https://web.archive.org/web/20120112213930/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F031.htm" target="_blank">https://web.archive.org/web/20120112213930/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F031.htm</a> <a href="#fnref:120" class="footnote-back-ref">↩</a></li>
<li id="fn:121">Meehl GA, et al. "Ch. 10: Global Climate Projections; Box 10.2: Equilibrium Climate Sensitivity". IPCC Fourth Assessment Report WG1 2007. Archived from the original on 9 June 2018. Retrieved 1 July 2018. <a href="https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10s10-5.html#box-10-2" target="_blank">https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10s10-5.html#box-10-2</a> <a href="#fnref:121" class="footnote-back-ref">↩</a></li>
<li id="fn:122">This article incorporates public domain material from "Ch. 6: Projected Future Greenhouse Gas Concentrations and Climate Change: Box 6.3: Climate sensitivity" (PDF). Technical Support Document for Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act. Washington, DC, USA: Climate Change Division, Office of Atmospheric Programs, US EPA. 7 December 2009. Archived (PDF) from the original on 1 December 2012. Retrieved 15 December 2012. (p.66 (p. 78 of PDF file)). <a href="/wiki/Copyright_status_of_works_by_the_federal_government_of_the_United_States" target="_blank">/wiki/Copyright_status_of_works_by_the_federal_government_of_the_United_States</a> <a href="#fnref:122" class="footnote-back-ref">↩</a></li>
<li id="fn:123">This article incorporates public domain material from "Ch. 6: Projected Future Greenhouse Gas Concentrations and Climate Change: Box 6.3: Climate sensitivity" (PDF). Technical Support Document for Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act. Washington, DC, USA: Climate Change Division, Office of Atmospheric Programs, US EPA. 7 December 2009. Archived (PDF) from the original on 1 December 2012. Retrieved 15 December 2012. (p.66 (p. 78 of PDF file)). <a href="/wiki/Copyright_status_of_works_by_the_federal_government_of_the_United_States" target="_blank">/wiki/Copyright_status_of_works_by_the_federal_government_of_the_United_States</a> <a href="#fnref:123" class="footnote-back-ref">↩</a></li>
<li id="fn:124">Hausfather Z (19 June 2018). "Explainer: How scientists estimate climate sensitivity". Carbon Brief. Archived from the original on 1 April 2020. Retrieved 14 March 2019. <a href="https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity" target="_blank">https://www.carbonbrief.org/explainer-how-scientists-estimate-climate-sensitivity</a> <a href="#fnref:124" class="footnote-back-ref">↩</a></li>
<li id="fn:125">Solomon S, et al. "Technical summary" (PDF). Climate Change 2007: Working Group I: The Physical Science Basis. Box TS.1: Treatment of Uncertainties in the Working Group I Assessment. Archived (PDF) from the original on 30 March 2019. Retrieved 30 March 2019., in IPCC AR4 WG1 2007 <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-ts-1.pdf" target="_blank">https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-ts-1.pdf</a> <a href="#fnref:125" class="footnote-back-ref">↩</a></li>
<li id="fn:126">"The CMIP6 landscape (Editorial)". Nature Climate Change. 9 (10): 727. 25 September 2019. Bibcode:2019NatCC...9..727.. doi:10.1038/s41558-019-0599-1. ISSN 1758-6798. <a href="https://doi.org/10.1038%2Fs41558-019-0599-1" target="_blank">https://doi.org/10.1038%2Fs41558-019-0599-1</a> <a href="#fnref:126" class="footnote-back-ref">↩</a></li>
<li id="fn:127">"New climate models suggest Paris goals may be out of reach". France 24. 14 January 2020. Archived from the original on 14 January 2020. Retrieved 18 January 2020. <a href="https://www.france24.com/en/20200114-new-climate-models-suggest-paris-goals-may-be-out-of-reach" target="_blank">https://www.france24.com/en/20200114-new-climate-models-suggest-paris-goals-may-be-out-of-reach</a> <a href="#fnref:127" class="footnote-back-ref">↩</a></li>
<li id="fn:128">Zelinka MD, Myers TA, McCoy DT, Po-Chedley S, Caldwell PM, Ceppi P, Klein SA, Taylor KE (2020). "Causes of Higher Climate Sensitivity in CMIP6 Models". Geophysical Research Letters. 47 (1): e2019GL085782. Bibcode:2020GeoRL..4785782Z. doi:10.1029/2019GL085782. hdl:10044/1/76038. ISSN 1944-8007. <a href="https://doi.org/10.1029%2F2019GL085782" target="_blank">https://doi.org/10.1029%2F2019GL085782</a> <a href="#fnref:128" class="footnote-back-ref">↩</a></li>
<li id="fn:129">"International analysis narrows range of climate's sensitivity to CO2". UNSW Newsroom. 23 July 2020. Archived from the original on 23 July 2020. Retrieved 23 July 2020. <a href="https://newsroom.unsw.edu.au/news/science-tech/international-analysis-narrows-range-climate%E2%80%99s-sensitivity-co2" target="_blank">https://newsroom.unsw.edu.au/news/science-tech/international-analysis-narrows-range-climate%E2%80%99s-sensitivity-co2</a> <a href="#fnref:129" class="footnote-back-ref">↩</a></li>
<li id="fn:130">"Increased warming in latest generation of climate models likely caused by clouds: New representations of clouds are making models more sensitive to carbon dioxide". Science Daily. 24 June 2020. Archived from the original on 26 June 2020. Retrieved 26 June 2020. <a href="https://www.sciencedaily.com/releases/2020/06/200624151600.htm" target="_blank">https://www.sciencedaily.com/releases/2020/06/200624151600.htm</a> <a href="#fnref:130" class="footnote-back-ref">↩</a></li>
<li id="fn:131">"Increased warming in latest generation of climate models likely caused by clouds: New representations of clouds are making models more sensitive to carbon dioxide". Science Daily. 24 June 2020. Archived from the original on 26 June 2020. Retrieved 26 June 2020. <a href="https://www.sciencedaily.com/releases/2020/06/200624151600.htm" target="_blank">https://www.sciencedaily.com/releases/2020/06/200624151600.htm</a> <a href="#fnref:131" class="footnote-back-ref">↩</a></li>
<li id="fn:132">Zelinka MD, Myers TA, McCoy DT, Po-Chedley S, Caldwell PM, Ceppi P, Klein SA, Taylor KE (2020). "Causes of Higher Climate Sensitivity in CMIP6 Models". Geophysical Research Letters. 47 (1): e2019GL085782. Bibcode:2020GeoRL..4785782Z. doi:10.1029/2019GL085782. hdl:10044/1/76038. ISSN 1944-8007. <a href="https://doi.org/10.1029%2F2019GL085782" target="_blank">https://doi.org/10.1029%2F2019GL085782</a> <a href="#fnref:132" class="footnote-back-ref">↩</a></li>
<li id="fn:133">Palmer, Tim (26 May 2020). "Short-term tests validate long-term estimates of climate change". Nature. 582 (7811): 185–186. Bibcode:2020Natur.582..185P. doi:10.1038/d41586-020-01484-5. PMID 32457461. <a href="https://doi.org/10.1038%2Fd41586-020-01484-5" target="_blank">https://doi.org/10.1038%2Fd41586-020-01484-5</a> <a href="#fnref:133" class="footnote-back-ref">↩</a></li>
<li id="fn:134">Watts, Jonathan (13 June 2020). "Climate worst-case scenarios may not go far enough, cloud data shows". The Guardian. ISSN 0261-3077. Archived from the original on 19 June 2020. Retrieved 19 June 2020. <a href="https://www.theguardian.com/environment/2020/jun/13/climate-worst-case-scenarios-clouds-scientists-global-heating" target="_blank">https://www.theguardian.com/environment/2020/jun/13/climate-worst-case-scenarios-clouds-scientists-global-heating</a> <a href="#fnref:134" class="footnote-back-ref">↩</a></li>
<li id="fn:135">Voosen, Paul (4 May 2022). "Use of 'too hot' climate models exaggerates impacts of global warming". www.science.org. Retrieved 12 January 2025. <a href="https://www.science.org/content/article/use-too-hot-climate-models-exaggerates-impacts-global-warming" target="_blank">https://www.science.org/content/article/use-too-hot-climate-models-exaggerates-impacts-global-warming</a> <a href="#fnref:135" class="footnote-back-ref">↩</a></li>
<li id="fn:136">Bender M (7 February 2020). "Climate Change Predictions Have Suddenly Gone Catastrophic. This Is Why". Vice. Archived from the original on 10 February 2020. Retrieved 9 February 2020. <a href="https://www.vice.com/en_uk/article/9393jd/climate-change-predictions-have-suddenly-gone-catastrophic-this-is-why" target="_blank">https://www.vice.com/en_uk/article/9393jd/climate-change-predictions-have-suddenly-gone-catastrophic-this-is-why</a> <a href="#fnref:136" class="footnote-back-ref">↩</a></li>
<li id="fn:137">Voosen, Paul (19 April 2019). "New climate models forecast a warming surge". Science. 364 (6437): 222–223. Bibcode:2019Sci...364..222V. doi:10.1126/science.364.6437.222. PMID 31000644. <a href="https://www.science.org/doi/10.1126/science.364.6437.222" target="_blank">https://www.science.org/doi/10.1126/science.364.6437.222</a> <a href="#fnref:137" class="footnote-back-ref">↩</a></li>
<li id="fn:138">Hausfather, Zeke; Marvel, Kate; Schmidt, Gavin A.; Nielsen-Gammon, John W.; Zelinka, Mark (May 2022). "Climate simulations: recognize the 'hot model' problem". Nature. 605 (7908): 26–29. Bibcode:2022Natur.605...26H. doi:10.1038/d41586-022-01192-2. PMID 35508771. <a href="https://www.nature.com/articles/d41586-022-01192-2" target="_blank">https://www.nature.com/articles/d41586-022-01192-2</a> <a href="#fnref:138" class="footnote-back-ref">↩</a></li>
<li id="fn:139">Voosen, Paul (27 July 2021). "U.N. climate panel confronts implausibly hot forecasts of future warming". www.science.org. Retrieved 12 January 2025. <a href="https://www.science.org/content/article/un-climate-panel-confronts-implausibly-hot-forecasts-future-warming" target="_blank">https://www.science.org/content/article/un-climate-panel-confronts-implausibly-hot-forecasts-future-warming</a> <a href="#fnref:139" class="footnote-back-ref">↩</a></li>
<li id="fn:140">Berardelli, Jeff (1 July 2020). "Some new climate models are projecting extreme warming. Are they correct?". Yale Climate Connections. Yale University. <a href="https://yaleclimateconnections.org/2020/07/some-new-climate-models-are-projecting-extreme-warming-are-they-correct/" target="_blank">https://yaleclimateconnections.org/2020/07/some-new-climate-models-are-projecting-extreme-warming-are-they-correct/</a> <a href="#fnref:140" class="footnote-back-ref">↩</a></li>
<li id="fn:141">Hausfather, Zeke; Marvel, Kate; Schmidt, Gavin A.; Nielsen-Gammon, John W.; Zelinka, Mark (May 2022). "Climate simulations: recognize the 'hot model' problem". Nature. 605 (7908): 26–29. Bibcode:2022Natur.605...26H. doi:10.1038/d41586-022-01192-2. PMID 35508771. <a href="https://www.nature.com/articles/d41586-022-01192-2" target="_blank">https://www.nature.com/articles/d41586-022-01192-2</a> <a href="#fnref:141" class="footnote-back-ref">↩</a></li>
<li id="fn:142">Voosen, Paul (4 May 2022). "Use of 'too hot' climate models exaggerates impacts of global warming". www.science.org. Retrieved 12 January 2025. <a href="https://www.science.org/content/article/use-too-hot-climate-models-exaggerates-impacts-global-warming" target="_blank">https://www.science.org/content/article/use-too-hot-climate-models-exaggerates-impacts-global-warming</a> <a href="#fnref:142" class="footnote-back-ref">↩</a></li>
</ol>

Climate sensitivity open-in-new

Climate sensitivity