Could the Pliocene constrain the equilibrium climate sensitivity?

Abstract. The mid-Pliocene Warm Period (mPWP) is the most recent interval in which atmospheric carbon dioxide was substantially higher than in modern pre-industrial times. It is, therefore, a potentially valuable target for testing the ability of climate models to simulate climates warmer than the pre-industrial state. The recent Pliocene Model Intercomparison Project (PlioMIP) presented boundary conditions for the mPWP and a protocol for climate model experiments. Here we analyse results from the PlioMIP and, for the first time, discuss the potential for this interval to usefully constrain the equilibrium climate sensitivity. We observe a correlation in the ensemble between their tropical temperature anomalies at the mPWP and their equilibrium sensitivities. If the real world is assumed to also obey this relationship, then the reconstructed tropical temperature anomaly at the mPWP can in principle generate a constraint on the true sensitivity. Directly applying this methodology using available data yields a range for the equilibrium sensitivity of 1.9–3.7 °C, but there are considerable additional uncertainties surrounding the analysis which are not included in this estimate. We consider the extent to which these uncertainties may be better quantified and perhaps lessened in the next few years.

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Could the Pliocene constrain the Equilibrium Climate Sensitivity?

10.5194/cp-2015-189 ◽

2016 ◽

Author(s):

J. C. Hargreaves ◽

J. D. Annan

Keyword(s):

Carbon Dioxide ◽

Boundary Conditions ◽

Climate Sensitivity ◽

Atmospheric Carbon Dioxide ◽

Climate Models ◽

Climate Model ◽

Equilibrium Climate Sensitivity ◽

Model Experiments ◽

First Time ◽

Industrial State

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Including the efficacy of land ice changes in deriving climate sensitivity from paleodata

10.5194/esd-2018-88 ◽

2018 ◽

Author(s):

Lennert B. Stap ◽

Peter Köhler ◽

Gerrit Lohmann

Keyword(s):

Climate Sensitivity ◽

Radiative Forcing ◽

Climate Models ◽

Climate Model ◽

Temperature Anomaly ◽

Global Temperature ◽

Radiative Forcings ◽

Intercomparison Project ◽

The Impact

Abstract. The influence of long-term processes in the climate system, such as land ice changes, has to be compensated for when comparing climate sensitivity derived from paleodata with equilibrium climate sensitivity (ECS) calculated by climate models, which is only generated by a CO2 change. Several recent studies found that the impact these long-term processes have on global temperature cannot be quantified directly through the global radiative forcing they induce. This renders the approach of deconvoluting paleotemperatures through a partitioning based on radiative forcings inaccurate. Here, we therefore implement an efficacy factor ε[LI], that relates the impact of land ice changes on global temperature to that of CO2 changes, in our calculation of climate sensitivity from paleodata. We apply our new approach to a proxy-inferred paleoclimate dataset, and find an equivalent ECS of 5.6 ± 1.3 K per CO2 doubling. The substantial uncertainty herein is generated by the range in ε[LI] we use, which is based on a multi-model assemblage of simulated relative influences of land ice changes on the Last Glacial Maximum (LGM) temperature anomaly (46 ± 14 %). The low end of our ECS estimate, which concurs with estimates from other approaches, tallies with a large influence for land ice changes. To separately assess this influence, we analyse output of the PMIP3 climate model intercomparison project. From this data, we infer a functional intermodel relation between global and high-latitude temperature changes at the LGM with respect to the pre-industrial climate, and the temperature anomaly caused by a CO2 change. Applying this relation to our dataset, we find a considerable 64 % influence for land ice changes on the LGM temperature anomaly. This is even higher than the range used before, and leads to an equivalent ECS of 3.8 K per CO2 doubling. Together, our results suggest that land ice changes play a key role in the variability of Late Pleistocene temperatures.

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Estimating Remaining Carbon Budgets Using Emulators of CMIP6 Models

10.21203/rs.3.rs-104000/v1 ◽

2020 ◽

Author(s):

Martin Rypdal ◽

Niklas Boers ◽

Hege-Beate Fredriksen ◽

Kai-Uwe Eiselt ◽

Andreas Johansen ◽

...

Keyword(s):

Climate Sensitivity ◽

Carbon Budget ◽

Climate Models ◽

Coupled Model ◽

Model Intercomparison ◽

Equilibrium Climate Sensitivity ◽

Uncertainty Range ◽

The Public ◽

Intercomparison Project ◽

Specific Temperature

Abstract A remaining carbon budget (RCB) estimates how much CO2 we can emit and still reach a specific temperature target. The RCB concept is attractive since it easily communicates to the public and policymakers, but RCBs are also subject to uncertainties. The expected warming levels for a given carbon budget has a wide uncertainty range, which we show here to increase with less ambitious targets, i.e., with higher CO2 emissions and temperatures. We demonstrate that the leading cause of the revealed RCB uncertainty is the spread in the equilibrium climate sensitivity (ECS) among climate models. In the Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble, the models with the lower ECS predict an RCB that is twice as high as that of models with the higher ECS, for temperature targets between 1.5-3.0°C.

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The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): Experimental design and forcing input data

10.5194/gmd-2016-68 ◽

2016 ◽

Cited By ~ 2

Author(s):

Davide Zanchettin ◽

Myriam Khodri ◽

Claudia Timmreck ◽

Matthew Toohey ◽

Anja Schmidt ◽

...

Keyword(s):

Climate Models ◽

Climate Model ◽

Initial Conditions ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Aerosol Layer ◽

Model Intercomparison ◽

Climatic Response ◽

Volcanic Forcing ◽

Intercomparison Project

Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Climate Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the model intercomparison project on the climate response to volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol dataset for each experiment to eliminate differences in the applied volcanic forcing, and defines a set of initial conditions to determine how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically-forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input datasets to be used.

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The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity

Climate of the Past ◽

10.5194/cp-16-2095-2020 ◽

2020 ◽

Vol 16 (6) ◽

pp. 2095-2123 ◽

Cited By ~ 4

Author(s):

Alan M. Haywood ◽

Julia C. Tindall ◽

Harry J. Dowsett ◽

Aisling M. Dolan ◽

Kevin M. Foley ◽

...

Keyword(s):

Climate Sensitivity ◽

Large Scale ◽

Climate Models ◽

Temperature Response ◽

Surface Air Temperature ◽

System Response ◽

Phase 2 ◽

Model Intercomparison ◽

Intergovernmental Panel ◽

Intercomparison Project

Abstract. The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ∼400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.7 and 5.2 ∘C relative to the pre-industrial era with a multi-model mean value of 3.2 ∘C. Annual mean total precipitation rates increase by 7 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases by 4.3 ∘C over land and 2.8 ∘C over the oceans. There is a clear pattern of polar amplification with warming polewards of 60∘ N and 60∘ S exceeding the global mean warming by a factor of 2.3. In the Atlantic and Pacific oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. There is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO2 (including ice sheet feedbacks) is 67 % greater than ECS; this is larger than the increase of 47 % obtained from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea surface temperatures are used to assess model estimates of ECS and give an ECS range of 2.6–4.8 ∘C. This result is in general accord with the ECS range presented by previous Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.

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Effective radiative forcing and adjustments in CMIP6 models

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-9591-2020 ◽

2020 ◽

Vol 20 (16) ◽

pp. 9591-9618 ◽

Cited By ~ 9

Author(s):

Christopher J. Smith ◽

Ryan J. Kramer ◽

Gunnar Myhre ◽

Kari Alterskjær ◽

William Collins ◽

...

Keyword(s):

Climate Sensitivity ◽

Radiative Forcing ◽

Climate Models ◽

Coupled Model ◽

Internal Variability ◽

Cmip5 Models ◽

Model Intercomparison ◽

Aerosol Forcing ◽

Intercomparison Project ◽

Effective Radiative Forcing

Abstract. The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.

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Reduced Complexity Model Intercomparison Project (RCMIP)

10.5194/egusphere-egu21-3707 ◽

2021 ◽

Author(s):

Zebedee Nicholls ◽

Keyword(s):

Climate Models ◽

Climate Model ◽

Model Intercomparison ◽

Specific Behaviour ◽

Form Part ◽

Scientific Outputs ◽

Science Policy Interface ◽

Model Hierarchy ◽

Intercomparison Project ◽

Reduced Complexity

<p>Reduced-complexity climate models form part of the climate model hierarchy and are increasingly relied upon at the science-policy interface. Historically, evaluation of reduced-complexity climate models has been limited to a number of independent studies. Here we present the reduced-complexity model intercomparison project (RCMIP), the first systematic, community-organised evaluation of reduced-complexity climate models. We introduce the motivation behind RCMIP, where to find information about it and key insights arising from its first two scientific outputs. Future phases of RCMIP will examine specific behaviour of reduced-complexity climate models in more detail, for example their carbon cycle response. We are particulalry keen to hear from users of reduced-complexity models to discuss their use cases, how we can evaluate our models in the way most relevant to them and where key model improvements can be made.</p>

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The Brewer-Dobson circulation in CMIP6

10.5194/egusphere-egu21-15246 ◽

2021 ◽

Author(s):

Natalia Calvo ◽

Marta Abalos ◽

Samuel Benito-Barca ◽

Hella Garny ◽

Steven Hardiman ◽

...

Keyword(s):

Climate Variability ◽

Surface Temperature ◽

Climate Model ◽

Model Intercomparison ◽

Residual Circulation ◽

Careful Evaluation ◽

Deep Branch ◽

Surface Climate ◽

Intercomparison Project ◽

First Time

<div> <div> <div> <p>The Brewer-Dobson circulation (BDC) is a key feature of the stratosphere that models need to accurately represent in order to improve the representation of surface climate variability. For the first time, the Climate Model Intercomparison Project includes in its phase 6 (CMIP6) a set of diagnostics that allow for careful evaluation of the BDC. Here, the BDC is evaluated against observations and reanalyses using historical simulations. CMIP6 results confirm the well-known inconsistency in BDC trends between observations and models in the middle and upper stratosphere. The increasing CO2 simulations feature a robust acceleration of the BDC but also reveal large uncertainties in the deep branch trends. The very close connection between the shallow branch and surface temperature is highlighted, which is absent in the deep branch. The trends in mean age of air are shown to be more robust throughout the stratosphere than those in the residual circulation.</p> </div> </div> </div>

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Probabilistic climate projections with Minimal CMIP Emulator (MCE)

10.5194/egusphere-egu21-13697 ◽

2021 ◽

Author(s):

Junichi Tsutsui

Keyword(s):

Climate Sensitivity ◽

Radiative Forcing ◽

Climate Models ◽

Model Parameters ◽

Climate Projections ◽

Second Phase ◽

Impulse Response Functions ◽

Model Intercomparison ◽

Probabilistic Climate Projections ◽

Intercomparison Project

<p>One of the key applications of simple climate models is probabilistic climate projections to assess a variety of emission scenarios in terms of their compatibility with global warming mitigation goals. The second phase of the Reduced Complexity Model Intercomparison Project (RCMIP) compares nine participating models for their probabilistic projection methods through scenario experiments, focusing on consistency with given constraints for climate indicators including radiative forcing, carbon budget, warming trends, and climate sensitivity. The MCE is one of the nine models, recently developed by the author, and has produced results that well match the ranges of the constraints. The model is based on impulse response functions and parameterized physics of effective radiative forcing and carbon uptake over ocean and land. Perturbed model parameters are generated from statistical models and constrained with a Metropolis-Hastings independence sampler. A parameter subset associated with CO<sub>2</sub>-induced warming is assured to have a covariance structure as diagnosed from complex climate models of the Coupled Model Intercomparison Project (CMIP). The model's simplicity and the successful results imply that a method with less complicated structures and fewer control parameters has an advantage when building reasonable perturbed ensembles in a transparent way despite less capacity to emulate detailed Earth system components. Experimental results for future scenarios show that the climate sensitivity of CMIP models is overestimated overall, suggesting that probabilistic climate projections need to be constrained with observed warming trends.</p>

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Statistisches Downscaling von CMIP6 Projektionen mit EPISODES

10.5194/dkt-12-45 ◽

2020 ◽

Author(s):

Philip Lorenz ◽

Frank Kreienkamp ◽

Tobias Geiger

Keyword(s):

Climate Sensitivity ◽

Coupled Model ◽

Model Intercomparison ◽

Equilibrium Climate Sensitivity ◽

Intercomparison Project

<p>Die Ergebnisse der Klimamodellierung, die im Rahmen des j&#252;ngsten Coupled Model Intercomparison Project (CMIP6) durchgef&#252;hrt wurden, zeigen signifikante Ver&#228;nderungen der modellspezifischen Gleichgewichtsklimaempfindlichkeit (Equilibrium Climate Sensitivity, ECS) im Vergleich zum Vorg&#228;ngerprojekt CMIP5. Die neueren Versionen vieler globaler Klimamodelle (GCMs) weisen h&#246;here ECS-Werte auf, die zu einer st&#228;rkeren globalen Erw&#228;rmung f&#252;hren als zuvor berechnet. Gleichzeitig ist die Multi-GCM-Streuung von ECS unter CMIP6 deutlich gr&#246;&#223;er als unter CMIP5.</p> <p>Ein Teil der im Rahmen von CMIP6 durchgef&#252;hrten Klimaprojektionen wurden mittels der am DWD entwickelten statistisch-empirischen Downscaling-Methode EPISODES f&#252;r das Gebiet von Deutschland regionalisiert. Diese Ergebnisse wurden mit vergleichbaren Datens&#228;tzen der CMIP5-L&#228;ufe verglichen. Die Ergebnisse dieser Analysen werden vorgestellt.</p>

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