Forcing, feedback, and climate sensitivity in cmip6 mark zelinka, tim myers, dan mccoy, stephen pochedley. Understanding climate sensitivity is critical to projecting climate change in response to a given forcing scenario. Sensitivity climate sensitivity sensitivity is related to climate feedbacks and has to do with the amount of positive or negative forcing that occurs in response to a given climate forcing. Evaluating emergent constraints on equilibrium climate sensitivity. In this study, these metrics are analyzed in a climate system model newly developed by the chinese academy of. The increase in climate sensitivity is unrelated to model tuning as all. Sep 16, 20 the range of climate sensitivity of cmip5 models is similar to the range found in previous generation models. These include the aforementioned models with high climate sensitivity. This study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the fifth phase of the coupled model intercomparison project cmip5, and analyzes intermodel differences. Climate sensitivity and feedbacks of a new coupled model camscsm to idealized co2 forcing. For cmip5, this is too computationally expensive for aogcms, but large step forcing experiments are still a very useful science tool for evaluating and comparing forcing and feedback processes. Energy budget constraints on climate sensitivity in light.
Energy budget constraints on climate sensitivity in light of inconstant climate feedbacks. Climate sensitivity is the temperature response to an increment in forcing in the case of no feedbacks due to the stefan boltzman stabilization term with t288k. Recently, the cloud feedback model intercomparison project bony et al. Climate sensitivity and feedbacks of a new coupled model cams. What can decadal variability tell us about climate. T in any scenario where f is constant such as abrupt co 2 quadrupling experiments. Radiative forcing, radiative adjustments, and radiative feedbacks in cmip5 models, j. This is done by taking into account the fact that the climate response to increased carbon dioxide co2 is not necessarily only. Forcing, feedbacks and climate sensitivity in cmip5 coupled atmosphereocean climate models timothy andrews,1 jonathan m. Climate sensitivity and feedbacks are basic and important metrics to a climate system. Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. May 28, 20 climate sensitivity is the temperature response to an increment in forcing.
Climate, climate forcings, climate sensitivity, and. Quantifying climate forcings and feedbacks over the last. Working group i contribution to the fourth assessment report of the intergovernmental panel on climate change, faq 1. The term feedback is used ubiquitously in climate research, but implies varied meanings in different contexts. Sst,f sst, and regression, f and various climate feedback terms. Battisti department of atmospheric sciences, university of washington, seattle, washington j. Pdf on the increased climate sensitivity in the ecearth.
Many modelling groups that contribute to cmip6 coupled model intercomparison project phase 6 have found a larger equilibrium climate. Forcing, feedbacks and climate sensitivity in cmip5 coupled atmosphereocean climate models. On the interpretation of intermodel spread in cmip5. The implications for climate sensitivity of ar5 forcing and. This is done by taking into account the fact that the climate response to increased carbon dioxide co2 is not necessarily only mediated. It is important to understand feedbacks in order to further quantify the risk factors and time scales involved with climate change. Contributions of radiative forcing and climate feedbacks to. As the 69 spread of climate sensitivity arises primarily from the tropics, we analyze in section 4 intermodel di. E forcing, feedbacks and climate sensitivity in cmip5 coupled. We estimate global mean temperature variations and s using a 784,000yearlong field reconstruction of sea surface.
Forcing, feedbacks and climate sensitivity in cmip5. The effective climate sensitivity effcs to a doubling of co 2 is 5. We analyze the radiative forcing, feedback, and sensitivity in the cmip5 gcms using the data from four experiments. Radiative forcing or climate forcing is the difference between insolation absorbed by the earth and energy radiated back to space. Ecs is then calculated from forcing f and net feedback. The dependence of radiative forcing and feedback on evolving.
Climate forcing noaas global monitoring division explains key attributes to climate forcing and offers potential actions that can be taken to reduce human impacts. The dependence of radiative forcing and feedback on evolving patterns of surface temperature change in climate models timothy andrews met of. We quantify forcing and feedbacks across available cmip5 coupled atmosphereocean general circulation models aogcms by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. Climate sensitivity estimates depend critically on radiative. In the end the whole climate debate boils down to just one thing climate sensitivity. Climate models predict a range of water vapor feedbacks of 1. Comparison of the 2xco 2 equilibrium climate sensitivity, 4xco 2 adjusted radiative forcing from fixed. Wcrp coupled model intercomparison project phase 5 cmip5 in 2008 the wcrp working group on coupled modelling wgcm, at its 12th session, endorsed the cmip5 protocol, which defined a set of thirtyfive climate model experiments designed to be useful in 1 assessing the mechanisms responsible for model differences in poorly understood feedbacks associated with the carbon cycle and with. Pdf on the increased climate sensitivity in the ecearth model. Forcing, feedback, and climate sensitivity in cmip6.
Apr 17, 2017 energy budget constraints on climate sensitivity in light of inconstant climate feedbacks. Radiative feedbacks are known to determine climate sensitivity. Atwood school of oceanography, university of washington, seattle, washington e. However, water vapor and lapse rate feedbacks are often combined into a single feedback, because stronger water vapor feedbacks also tend to produce stronger lapse rate feedbacks. This is the fourth in a series of four articles on historical and projected climate extremes in the united states. Implications of potentially lower climate sensitivity on. Recent analyses 1,2,3 have suggested that transient climate sensitivity is at. Uncertainty in future projections will only be reduced if cloud responses induced directly by radiative forcing as well as feedbacks linked to mean global temperature can be accurately represented. Climate sensitivity and cmip5 climate sensitivity helps us understand the cause of this uncertainty in cmip5, we are also likely to have a range of projections, so we will need to explain why different models respond differently to the same external forcing cmip3 projections. Cmip phase 5 cmip5 world climate research programme. On the interpretation of intermodel spread in cmip5 climate. Climate sensitivity and cloud feedback processes imposed by. Note the irf figure and values were corrected on 3122016 to account for a missing forcing in the all forcings case. Causes of higher climate sensitivity in cmip6 models.
For cmip5 models, both forcing and feedback information are taken from table 1 of caldwell et al. The improved cmip6 models do not exhibit this spurious negative cloud feedback. We quantify forcing and feedbacks across available cmip5 coupled atmosphereocean general circulation models aogcms by analysing simulations forced by. Global topofatmosphere radiation correlations with surface temperature performed here show that decadal variability in surface temperature is also reinforced by strong positive feedbacks in models, both in the long wave lw and short wave sw, offsetting much of the planck radiative damping. The strengthened cloud feedback in cmip6 comes from an enhanced shortwave sw component that is only slightly opposed by a weaker longwave component. Climate sensitivity is usually expressed in degrees per doubling of atmospheric carbon dioxide co 2, a forcing of about 4 wm 2. A climate feedback is an indirect, or secondary, changeeither positive or negativethat occurs within the climate system in response to a forcing mechanism. We summarize here forcing datasets used in giss global climate models over the years. Dec 12, 2017 climate feedbacks generally become smaller in magnitude over time under co 2 forcing in coupled climate models, leading to an increase in the effective climate sensitivity, the estimated globalmean surface warming in steady state for doubled co 2. Climate sensitivity is the change in surface air temperature per unit change in radiative forcing, and the climate sensitivity parameter is therefore expressed in units of cwm 2. However, forcing estimates from cmip5 models often include rapid. Note that the sign convention is the opposite of that followed by gregory et al. Future temperatures in cmip6 span a broader range than in cmip5, with the upper range of the multimodel ensemble exceeding that of cmip5.
Timevarying climate sensitivity from regional feedbacks. Climate sensitivity and feedbacks are basic and important metrics to a. This is done by taking into account the fact that the climate. The sensitivity of the earths climate to increases in atmospheric co2 concentration is a question that sits at the heart of climate science essentially, it dictates how much global temperatures will rise in response to humancaused co2 emissions, but it is a question that does not yet have a clear answer. Despite the importance of the carbon cycle and its feedback on the climate system, the cmip5 experiment protocol was designed to allow participation of groups having a climate model without an interactive carbon cycle as well as. Uncertainties in cmip5 climate projections due to carbon. Equilibrium climate sensitivity ecs, the equilibrium globalmean surface. The models are ordered from left to right in order of their equilibrium climate sensitivity. The magnitude of this warming at equilibrium for a given radiative forcing referred to as specific equilibrium climate sensitivity s is still subject to uncertainties. For example, suppose that a disturbance caused global temperatures to increase. An estimate of ecs made in this way from a nonequilibrium experiment is sometimes called effective climate sensitivity murphy, 1995, but we will refer to it as ecs for convenience. In contrast to idealized model studies of climate sensitivity, realworld climate forcing and change are time dependent and involve nonlinear coupled atmosphereocean processes and heat exchanges between the ocean mixed layer and deep ocean that require an aogcm i.
Mar 23, 20 this study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the fifth phase of the coupled model intercomparison project cmip5, and analyzes intermodel differences. Contributions of radiative forcing and climate feedbacks. Positive radiative forcing means earth receives more incoming energy from sunlight than it radiates to space. Reconciled climate response estimates from climate models. Differences in cloud feedbacks continue to be important contributors to this range. The regional climate feedbacks formulation also reveals fundamental biases in a widely used method for diagnosing climate sensitivity, feedbacks, and radiative forcingthe regression of the global topofatmosphere radiation flux on global surface temperature. Data for these figures are available here and here. Forcing, feedback and internal variability in global.
Therefore, the positive tropical cloud feedbacks that are still present in these models, are no longer balanced by this negative feedback, resulting in a larger positive net cloud feedback and an increase in climate sensitivity. In the case of no feedbacks due to the stefan boltzman stabilization term with t288k. We examine the tropical inversion strength, measured by the estimated inversion strength eis, and its response to climate change in 18 models associated with phase 5 of the coupled model intercomparison project cmip5. This is the first application of the linear forcing feedback regression analysis of gregory et al. Equilibrium climate sensitivity ecs and transient climate response. Climate sensitivity and cloud feedback processes imposed. The effects of ocean heat uptake on transient climate. Feedbacks, climate sensitivity and the limits of linear. Co2 earth system sensitivity is higher than this, being. This is the first application of the linear forcingfeedback regression analysis of gregory et al. Quantifying climate forcings and feedbacks over the last millennium in the cmip5 pmip3 models. Pdf climate sensitivity and feedbacks of a new coupled. What climate sensitivity index is most useful for projections.
From a specific process that locally affects a quantity, to a formal framework that attempts to determine a global response to a forcing, researchers use this term to separate, simplify and quantify parts of the complex earth system. Nov, 2015 climate sensitivity is not a quantity that can be measured, and it characterizes only a part of the relevant processes and feedbacks, but it is an emerging property of the system. The range of climate sensitivity of cmip5 models is similar to the range found in previous generation models. While cmip5 models generally capture the geographic distribution of observed eis, they systematically underestimate it off the west coasts of continents, due to a warm. A recently published paper by hansen and sato 2011, paleoclimate implications for humanmade climate change, examines evidence from past climates about the various feedbacks that affect climate sensitivity. The concepts of radiative forcing rf and climate feedbacks continue to be re. Abstract this study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the fifth phase of the coupled model intercomparison project cmip5, and analyzes intermodel differences. Forcings, feedbacks, and climate sensitivity in hadgem3. E forcing, feedbacks and climate sensitivity in cmip5. Energy budget and climate model estimates of transient climate response match when model output is processed in the same manner as an observational record.
On the climate sensitivity and historical warming evolution in. The dependence of radiative forcing and feedback on. The coupled model intercomparison project phase 5 cmip5 model spread in. Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing, and so play an important part in determining the climate sensitivity and future climate state. Operated by lawrence livermore national security, llc, for the department of. In this study, we investigated forcing, feedbacks, and climate sensitivity in abrupt co quadrupling experiments conducted in the latest generation of fully coupled gcms as part of cmip6, with an eye toward determining similarities with and differences from the previous generation of models. Keywords climate sensitivity feedback radiative forcing fast adjustment radiative kernel cmip5 climate model simulations climate change intermodel spread 1 introduction the equilibrium globalmean surface temperature change associated with a doubling of co 2 concentration in the atmosphere is referred to as climate sensitivity. Andrews t, gregory j m, webb m j and taylor k e 2012 forcing, feedbacks and climate sensitivity in. Relationship of tropospheric stability to climate sensitivity. Uncertainties in cmip5 climate projections due to carbon cycle feedbacks pierre friedlingstein, malte meinshausen,1 vivek k. Effective radiative forcing erf, climate sensitivity and climate feedbacks estimated for the cmip5 aogcms see table 9.
Changes to earths radiative equilibrium, that cause temperatures to rise or fall over decadal periods, are called climate forcings. The sensitivity of the climate system to a forcing is commonly expressed in terms of the global mean temperature change that would be expected after a time sufficiently long for both the atmosphere and ocean to come to equilibrium with the change in climate forcing. The strength of the tropical inversion and its response to. Climate chung and soden, 2015b, an assessment of methods for computing radiative forcing in climate models, env. Dec 14, 2016 and that puts a maximum limit on the climate sensitivity, which is that the climate sensitivity cannot be larger than one degree c per 11. Forcing, feedbacks and climate sensitivity in cmip5 coupled. Climate forcing and feedback in the azimuth project. Here, we show that the evolution of climate feedbacks in models is consistent with the effect of. We quantify forcing and feedbacks across available cmip5 coupled atmosphereocean general circulation models aogcms by analysing simulations forced by an abrupt quadrupling of atmospheric carbon. Download scientific diagram equilibrium climate sensitivity ecs and transient climate response tcr of 23 cmip5 models. We quantify forcing and feedbacks across available cmip5 coupled atmosphere. A major goal of climate modeling is to provide better estimates of ecs and its uncertainty. Quantifying global climate feedbacks, responses and forcing under abrupt and gradual co2 forcing. Climate forcing, sensitivity, and feedback metrics are evaluated in both the united kingdoms physical climate model hadgem3.
On the interpretation of intermodel spread in cmip5 climate sensitivity estimates 3 68 di. Energy budget constraints on climate sensitivity in light of. Wcrp coupled model intercomparison project phase 5 cmip5 in 2008 the wcrp working group on coupled modelling wgcm, at its 12th session, endorsed the cmip5 protocol, which defined a set of thirtyfive climate model experiments designed to be useful in 1 assessing the mechanisms responsible for model differences in poorly understood feedbacks associated with the carbon cycle and with clouds. Nonlinear climate sensitivity and its implications for.
Cmip5 coupled atmosphereocean climate models geophys. Uncertainty in future projections will only be reduced if cloud responses induced directly by radiative forcing as well as feedbacks linked to. The climate reacts to any increase or decrease in forcing by radiating a little more or a little less energy from the surface. Calculations and descriptions of the forcings in the giss cmip5 simulations 18502012 can be found in miller et al. How carboncycle feedbacks could make global warming. Erf, equilibrium climate sensitivity ecs and transient climate response tcr are based on andrews et al. They determine how large surface air temperature will increase under co 2 forcing ultimately, which is essential for carbon reduction policies to achieve a specific warming target.
This is solely due to stronger positive cloud feedbacks, as the distributions of noncloud feedbacks and effective 4xco2 radiative forcing are nearly identical to those in cmip5. Both the multimodel mean and intermodel variance in. The objective of the coupled model intercomparison project cmip is to better understand past, present and future climate changes arising from natural, unforced variability or in response to changes in radiative forcing in a multimodel context. Quantifying climate forcings and feedbacks over the last millennium in the cmip5pmip3 models a. Here, we examine the results of historical and future climate model experiments from the phase 5 of the coupled model intercomparison project cmip5 based on work presented at the world climate research programme wcrp workshop on cmip5 climate model analyses held in. Note that the forcings are estimates that may be revised as new information or better understandings of the source data become available. Lawrence livermore national laboratory 7000 east avenue livermore, ca 94550. Mm resolution and the united kingdoms earth system model ukesm1. Climate emergent scale invariance and climate sensitivity html. From past climate, it can be approximated by relating equilibrium warming to radiative forcing. Pdf causes of higher climate sensitivity in cmip6 models.
The climate reacts to any increase or decrease in forcing by radiating a. Inhomogeneous forcing and transient climate sensitivity. Climate sensitivity is approximately the same, whatever the reason for the radiative forcing e. Climate sensitivity and feedbacks of a new coupled model. Pdf quantifying climate forcings and feedbacks over the. The combination of high climate sensitivity and high carboncycle feedbacks could result in substantial warming, even under more moderate emissions scenarios.