Atmosphere Response Time Scales Estimated from AOGCM Experiments

Abstract The global-mean surface air temperature response of the climate system to a specific radiative forcing shows characteristic time scales. Identifying these time scales and their corresponding amplitudes (climate sensitivity) allows one to approximate the response to arbitrary radiative forcings. The authors estimate these time scales for a set of atmosphere–ocean general circulation models (AOGCMs) based on relatively short integrations of 100–300 yr for some idealized forcings. Two modes can be clearly distinguished but a large spread in time scales and climate sensitivities exists among the AOGCMs. The analysis herein also shows that different factors influence the mode estimates. The value and uncertainty of the smallest time scale estimate is significantly lower when based on step scenarios than gradual scenarios; the uncertainty on the climate sensitivity of the slow mode can only be reduced significantly by performing longer AOGCM simulations; and scenarios with only a monotonically increasing forcing do not easily permit the climate sensitivity and the response time for the slow mode to be disentangled. Finally, climate sensitivities can be estimated more accurately than response times.

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Evaluating parametric sensitivity of climate feedbacks in CNRM-CM6

10.5194/egusphere-egu21-15730 ◽

2021 ◽

Author(s):

Saloua Peatier ◽

Benjamin Sanderson ◽

Laurent Terray

Keyword(s):

Climate Sensitivity ◽

General Circulation ◽

Temperature Response ◽

Coupled Model ◽

General Circulation Models ◽

Future Climate Change ◽

Climate Feedbacks ◽

Geophysical Research ◽

Physics Ensemble ◽

Earth’S Climate

The global surface temperature response to CO2 doubling (Equilibrium Climate Sensitivity or ECS) is a key uncertain parameter determining the extent of future climate change. Sherwood et al. (2020) estimated the ECS to be within [2.6K - 4.5K], but in the Coupled Model Intercomparison Project phase 6 (CMIP6), 1/3 of the General Circulation Models (GCMs) show ECS exceeding 4.5K (Zelinka et al., 2020). CNRM-CM6-1 is one of these models, with an ECS of 4.9K. In this paper, we sampled 30 atmospheric parameters of CNRM-CM6-1 and produced a Perturbed Physics Ensemble (PPE) of atmospheric-only simulations to explore the feedback parameters diversity and the climatological plausibility of the members. This PPE showed a comparable&#160; range of feedback parameters to the multi-model archive, from 0.8 W.m-2/K to 1.8 W.m-2/K. Emulators of climatological performance and feedback parameters were used together with&#160; observational datasets to search for optimal model configurations conditional on different net climate feedbacks. The climatological constraints considered here did not themselves rule out the higher end ECS values of 5K and above. An optimal subset of parameter configurations were chosen to sample the range of ECS allowing the assessment of feedback constraints in future fully coupled experiments.&#160;References :Sherwood, S. C., Webb, M. J., Annan, J. D., Armour, K. C., Forster, P. M., Hargreaves, J. C., ... & Zelinka, M. D. (2020). An assessment of Earth's climate sensitivity using multiple lines of evidence. Reviews of Geophysics, 58(4), e2019RG000678.Zelinka, M. D., Myers, T. A., McCoy, D. T., Po&#8208;Chedley, S., Caldwell, P. M., Ceppi, P., ... & Taylor, K. E. (2020). Causes of higher climate sensitivity in CMIP6 models. Geophysical Research Letters, 47(1), e2019GL085782.

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Contributors to linkage between Arctic warming and East Asian winter climate

Climate Dynamics ◽

10.1007/s00382-021-05820-x ◽

2021 ◽

Author(s):

Xinping Xu ◽

Shengping He ◽

Yongqi Gao ◽

Botao Zhou ◽

Huijun Wang

Keyword(s):

Sea Ice ◽

General Circulation ◽

Initial Conditions ◽

Wave Train ◽

East Asian ◽

Surface Air Temperature ◽

General Circulation Models ◽

The Arctic ◽

Winter Climate ◽

Arctic Warming

AbstractPrevious modelling and observational studies have shown discrepancies in the interannual relationship of winter surface air temperature (SAT) between Arctic and East Asia, stimulating the debate about whether Arctic change can influence midlatitude climate. This study uses two sets of coordinated experiments (EXP1 and EXP2) from six different atmospheric general circulation models. Both EXP1 and EXP2 consist of 130 ensemble members, each of which in EXP1 (EXP2) was forced by the same observed daily varying sea ice and daily varying (daily climatological) sea surface temperature (SST) for 1982–2014 but with different atmospheric initial conditions. Large spread exists among ensemble members in simulating the Arctic–East Asian SAT relationship. Only a fraction of ensemble members can reproduce the observed deep Arctic warming–cold continent pattern which extends from surface to upper troposphere, implying the important role of atmospheric internal variability. The mechanisms of deep Arctic warming and shallow Arctic warming are further distinguished. Arctic warming aloft is caused primarily by poleward moisture transport, which in conjunction with the surface warming coupled with sea ice melting constitutes the surface-amplified deep Arctic warming throughout the troposphere. These processes associated with the deep Arctic warming may be related to the forcing of remote SST when there is favorable atmospheric circulation such as Rossby wave train propagating from the North Atlantic into the Arctic.

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The relevance of mid-Holocene Arctic warming to the future

Climate of the Past ◽

10.5194/cp-15-1375-2019 ◽

2019 ◽

Vol 15 (4) ◽

pp. 1375-1394 ◽

Cited By ~ 6

Author(s):

Masakazu Yoshimori ◽

Marina Suzuki

Keyword(s):

Surface Temperature ◽

General Circulation ◽

Temperature Response ◽

Longwave Radiation ◽

General Circulation Models ◽

Cross Model ◽

Arctic Warming ◽

Temperature Changes ◽

The Future ◽

Arctic Climate Change

Abstract. There remain substantial uncertainties in future projections of Arctic climate change. There is a potential to constrain these uncertainties using a combination of paleoclimate simulations and proxy data, but such a constraint must be accompanied by physical understanding on the connection between past and future simulations. Here, we examine the relevance of an Arctic warming mechanism in the mid-Holocene (MH) to the future with emphasis on process understanding. We conducted a surface energy balance analysis on 10 atmosphere and ocean general circulation models under the MH and future Representative Concentration Pathway (RCP) 4.5 scenario forcings. It is found that many of the dominant processes that amplify Arctic warming over the ocean from late autumn to early winter are common between the two periods, despite the difference in the source of the forcing (insolation vs. greenhouse gases). The positive albedo feedback in summer results in an increase in oceanic heat release in the colder season when the atmospheric stratification is strong, and an increased greenhouse effect from clouds helps amplify the warming during the season with small insolation. The seasonal progress was elucidated by the decomposition of the factors associated with sea surface temperature, ice concentration, and ice surface temperature changes. We also quantified the contribution of individual components to the inter-model variance in the surface temperature changes. The downward clear-sky longwave radiation is one of major contributors to the model spread throughout the year. Other controlling terms for the model spread vary with the season, but they are similar between the MH and the future in each season. This result suggests that the MH Arctic change may not be analogous to the future in some seasons when the temperature response differs, but it is still useful to constrain the model spread in the future Arctic projection. The cross-model correlation suggests that the feedbacks in preceding seasons should not be overlooked when determining constraints, particularly summer sea ice cover for the constraint of autumn–winter surface temperature response.

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Towards a better representation of the solar cycle in general circulation models

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-5391-2007 ◽

2007 ◽

Vol 7 (20) ◽

pp. 5391-5400 ◽

Cited By ~ 59

Author(s):

K. M. Nissen ◽

K. Matthes ◽

U. Langematz ◽

B. Mayer

Keyword(s):

Solar Cycle ◽

Heating Rate ◽

General Circulation ◽

Temperature Response ◽

General Circulation Models ◽

Short Wave ◽

Radiative Transfer Model ◽

Transfer Model ◽

Heating Rates ◽

Radiation Scheme

Abstract. We introduce the improved Freie Universität Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%. The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal. Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60–70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy).

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Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-10083-2016 ◽

2016 ◽

Vol 16 (15) ◽

pp. 10083-10095 ◽

Cited By ~ 23

Author(s):

Nicholas A. Davis ◽

Dian J. Seidel ◽

Thomas Birner ◽

Sean M. Davis ◽

Simone Tilmes

Keyword(s):

Carbon Dioxide ◽

Radiative Forcing ◽

General Circulation ◽

Climate Models ◽

Temperature Response ◽

Austral Summer ◽

Hadley Cell ◽

Solar Constant ◽

Cell Width ◽

Climate Forcings

Abstract. Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of Earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidence stabilizes the atmosphere and suppresses precipitation. Understanding the primary drivers of tropical expansion is hampered by the myriad forcing agents in most model projections of future climate. While many previous studies have examined the response of idealized models to simplified climate forcings and the response of comprehensive climate models to more complex climate forcings, few have examined how comprehensive climate models respond to simplified climate forcings. To shed light on robust processes associated with tropical expansion, here we examine how the tropical belt width, as measured by the Hadley cell edges, responds to simplified forcings in the Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt expands in response to a quadrupling of atmospheric carbon dioxide concentrations and contracts in response to a reduction in the solar constant, with a range of a factor of 3 in the response among nine models. Models with more surface warming and an overall stronger temperature response to quadrupled carbon dioxide exhibit greater tropical expansion, a robust result in spite of inter-model differences in the mean Hadley cell width, parameterizations, and numerical schemes. Under a scenario where the solar constant is reduced to offset an instantaneous quadrupling of carbon dioxide, the Hadley cells remain at their preindustrial width, despite the residual stratospheric cooling associated with elevated carbon dioxide levels. Quadrupled carbon dioxide produces greater tropical belt expansion in the Southern Hemisphere than in the Northern Hemisphere. This expansion is strongest in austral summer and autumn. Ozone depletion has been argued to cause this pattern of changes in observations and model experiments, but the results here indicate that seasonally and hemispherically asymmetric tropical expansion can be a basic response of the general circulation to climate forcings.

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Climate hypersensitivity to solar forcing?

Annales Geophysicae ◽

10.1007/s00585-000-0583-z ◽

2000 ◽

Vol 18 (5) ◽

pp. 583-588 ◽

Cited By ~ 17

Author(s):

W. Soon ◽

E. Posmentier ◽

S. Baliunas

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Solar Physics ◽

Stratospheric Ozone ◽

General Circulation Models ◽

Static Stability ◽

Radiative Properties ◽

Balance Model ◽

Solar Forcing ◽

Solar Uv

Abstract. We compare the equilibrium climate responses of a quasi-dynamical energy balance model to radiative forcing by equivalent changes in CO2, solar total irradiance (Stot) and solar UV (SUV). The response is largest in the SUV case, in which the imposed UV radiative forcing is preferentially absorbed in the layer above 250 mb, in contrast to the weak response from global-columnar radiative loading by increases in CO2 or Stot. The hypersensitive response of the climate system to solar UV forcing is caused by strongly coupled feedback involving vertical static stability, tropical thick cirrus ice clouds and stratospheric ozone. This mechanism offers a plausible explanation of the apparent hypersensitivity of climate to solar forcing, as suggested by analyses of recent climatic records. The model hypersensitivity strongly depends on climate parameters, especially cloud radiative properties, but is effective for arguably realistic values of these parameters. The proposed solar forcing mechanism should be further confirmed using other models (e.g., general circulation models) that may better capture radiative and dynamical couplings of the troposphere and stratosphere.Key words: Meteorology and atmospheric dynamics (climatology · general or miscellaneous) · Solar physics · astrophysics · and astronomy (ultraviolet emissions)

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The faint young Sun problem revisited with a 3-D climate–carbon model – Part 1

Climate of the Past ◽

10.5194/cp-10-697-2014 ◽

2014 ◽

Vol 10 (2) ◽

pp. 697-713 ◽

Cited By ~ 5

Author(s):

G. Le Hir ◽

Y. Teitler ◽

F. Fluteau ◽

Y. Donnadieu ◽

P. Philippot

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Freezing Point ◽

Climatic Factors ◽

General Circulation Models ◽

Companion Paper ◽

One Dimensional ◽

Carbon Dioxide Concentrations ◽

Wide Range ◽

High Concentrations

Abstract. During the Archaean, the Sun's luminosity was 18 to 25% lower than the present day. One-dimensional radiative convective models (RCM) generally infer that high concentrations of greenhouse gases (CO2, CH4) are required to prevent the early Earth's surface temperature from dropping below the freezing point of liquid water and satisfying the faint young Sun paradox (FYSP, an Earth temperature at least as warm as today). Using a one-dimensional (1-D) model, it was proposed in 2010 that the association of a reduced albedo and less reflective clouds may have been responsible for the maintenance of a warm climate during the Archaean without requiring high concentrations of atmospheric CO2 (pCO2). More recently, 3-D climate simulations have been performed using atmospheric general circulation models (AGCM) and Earth system models of intermediate complexity (EMIC). These studies were able to solve the FYSP through a large range of carbon dioxide concentrations, from 0.6 bar with an EMIC to several millibars with AGCMs. To better understand this wide range in pCO2, we investigated the early Earth climate using an atmospheric GCM coupled to a slab ocean. Our simulations include the ice-albedo feedback and specific Archaean climatic factors such as a faster Earth rotation rate, high atmospheric concentrations of CO2 and/or CH4, a reduced continental surface, a saltier ocean, and different cloudiness. We estimated full glaciation thresholds for the early Archaean and quantified positive radiative forcing required to solve the FYSP. We also demonstrated why RCM and EMIC tend to overestimate greenhouse gas concentrations required to avoid full glaciations or solve the FYSP. Carbon cycle–climate interplays and conditions for sustaining pCO2 will be discussed in a companion paper.

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Large methane releases lead to strong aerosol forcing and reduced cloudiness

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-9057-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 9057-9081

Author(s):

T. Kurtén ◽

L. Zhou ◽

R. Makkonen ◽

J. Merikanto ◽

P. Räisänen ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Cloud Droplet ◽

Fold Increase ◽

General Circulation Models ◽

Large Temperature ◽

Atmospheric Lifetime ◽

Temperature Changes ◽

Aerosol Forcing ◽

Rapid Amplification

Abstract. The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70% increase in the atmospheric lifetime of methane, and an 18% decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing ("enhanced greenhouse effect") of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.

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PLASIM-ENTSem: a spatio-temporal emulator of future climate change for impacts assessment

Geoscientific Model Development Discussions ◽

10.5194/gmdd-6-3349-2013 ◽

2013 ◽

Vol 6 (2) ◽

pp. 3349-3380 ◽

Cited By ~ 5

Author(s):

P. B. Holden ◽

N. R. Edwards ◽

P. H. Garthwaite ◽

K. Fraedrich ◽

F. Lunkeit ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Coupled Model ◽

Co2 Concentration ◽

General Circulation Models ◽

Climate Impacts ◽

Future Climate ◽

Future Climate Change ◽

Climate Data ◽

Spatio Temporal

Abstract. Many applications in the evaluation of climate impacts and environmental policy require detailed spatio-temporal projections of future climate. To capture feedbacks from impacted natural or socio-economic systems requires interactive two-way coupling but this is generally computationally infeasible with even moderately complex general circulation models (GCMs). Dimension reduction using emulation is one solution to this problem, demonstrated here with the GCM PLASIM-ENTS. Our approach generates temporally evolving spatial patterns of climate variables, considering multiple modes of variability in order to capture non-linear feedbacks. The emulator provides a 188-member ensemble of decadally and spatially resolved (~ 5° resolution) seasonal climate data in response to an arbitrary future CO2 concentration and radiative forcing scenario. We present the PLASIM-ENTS coupled model, the construction of its emulator from an ensemble of transient future simulations, an application of the emulator methodology to produce heating and cooling degree-day projections, and the validation of the results against empirical data and higher-complexity models. We also demonstrate the application to estimates of sea-level rise and associated uncertainty.

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Diagnosing Cloud Feedbacks in General Circulation Models

Journal of Climate ◽

10.1175/jcli4140.1 ◽

2007 ◽

Vol 20 (11) ◽

pp. 2602-2622 ◽

Cited By ~ 8

Author(s):

Ping Zhu ◽

James J. Hack ◽

Jeffrey T. Kiehl

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Cloud Amount ◽

General Circulation Models ◽

Cloud Feedback ◽

Radiative Fluxes ◽

Cloud Feedbacks ◽

Flux Change ◽

Gfdl Model ◽

The Individual

Abstract In this study, it is shown that the NCAR and GFDL GCMs exhibit a marked difference in climate sensitivity of clouds and radiative fluxes in response to doubled CO2 and ±2-K SST perturbations. The GFDL model predicted a substantial decrease in cloud amount and an increase in cloud condensate in the warmer climate, but produced a much weaker change in net cloud radiative forcing (CRF) than the NCAR model. Using a multiple linear regression (MLR) method, the full-sky radiative flux change at the top of the atmosphere was successfully decomposed into individual components associated with the clear sky and different types of clouds. The authors specifically examined the cloud feedbacks due to the cloud amount and cloud condensate changes involving low, mid-, and high clouds between 60°S and 60°N. It was found that the NCAR and GFDL models predicted the same sign of individual longwave and shortwave feedbacks resulting from the change in cloud amount and cloud condensate for all three types of clouds (low, mid, and high) despite the different cloud and radiation schemes used in the models. However, since the individual longwave and shortwave feedbacks resulting from the change in cloud amount and cloud condensate generally have the opposite signs, the net cloud feedback is a subtle residual of all. Strong cancellations between individual cloud feedbacks may result in a weak net cloud feedback. This result is consistent with the findings of the previous studies, which used different approaches to diagnose cloud feedbacks. This study indicates that the proposed MLR approach provides an easy way to efficiently expose the similarity and discrepancy of individual cloud feedback processes between GCMs, which are hidden in the total cloud feedback measured by CRF. Most importantly, this method has the potential to be applied to satellite measurements. Thus, it may serve as a reliable and efficient method to investigate cloud feedback mechanisms on short-term scales by comparing simulations with available observations, which may provide a useful way to identify the cause for the wide spread of cloud feedbacks in GCMs.

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