On the future role of the most parsimonious  climate module in integrated assessment

Abstract. In the following, we test the validity of a one-box climate model as an emulator for atmosphere–ocean general circulation models (AOGCMs). The one-box climate model is currently employed in the integrated assessment models FUND, MIND, and PAGE, widely used in policy making. Our findings are twofold. Firstly, when directly prescribing AOGCMs' respective equilibrium climate sensitivities (ECSs) and transient climate responses (TCRs) to the one-box model, global mean temperature (GMT) projections are generically too high by 0.5 K at peak temperature for peak-and-decline forcing scenarios, resulting in a maximum global warming of approximately 2 K. Accordingly, corresponding integrated assessment studies might tend to overestimate mitigation needs and costs. We semi-analytically explain this discrepancy as resulting from the information loss resulting from the reduction of complexity. Secondly, the one-box model offers a good emulator of these AOGCMs (accurate to within 0.1 K for Representative Concentration Pathways, RCPs, namely RCP2.6, RCP4.5, and RCP6.0), provided the AOGCM's ECS and TCR values are universally mapped onto effective one-box counterparts and a certain time horizon (on the order of the time to peak radiative forcing) is not exceeded. Results that are based on the one-box model and have already been published are still just as informative as intended by their respective authors; however, they should be reinterpreted as being influenced by a larger climate response to forcing than intended.

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On the Future Role of the most Parsimonious Climate Module in Integrated Assessment

10.5194/esd-2017-40 ◽

2017 ◽

Author(s):

Mohammad M. Khabbazan ◽

Hermann Held

Keyword(s):

Integrated Assessment ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

General Circulation Models ◽

Box Model ◽

Global Mean Temperature ◽

The Future ◽

The One ◽

The Mind

Abstract. We test the validity of a one-box climate model as an emulator for Atmosphere-Ocean General Circulation Models (AOGCMs) when the application is confined to the subset of scenarios approximately in-line with the 2° target. The one-box climate model is currently in use in the integrated assessment models FUND and MIND. For our assessment, we crucially rely on 14 recent CMIP5 AOGCM diagnostics of the total radiative forcing for various representative concentration pathways. Our findings are two-fold. Firstly, when directly prescribing AOGCMs’ respective equilibrium climate sensitivities (ECSs) and transient climate responses (TCRs) to the one-box model, global mean temperature (GMT) projections are generically too large by 0.5 K at peak temperature. Accordingly, corresponding integrated assessment studies might overestimate mitigation need and cost. Secondly, the one-box model becomes an excellent emulator of those AOGCMs once their ECS and TCR values are universally mapped onto effective one-box intrinsic counterparts. We suggest utilizing this one-box model in integrated assessment also in the future, in particular when computationally demanding decision-making under climate response uncertainty might be modelled. However, then the roles of ECS and TCR must be re-interpreted. For the MIND model as used over the past 5 years, even the transformed ECS values comply with the ranges explicated by IPCC AR5, however now at the high-end.

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The cloud–aerosol–radiation (CAR) ensemble modeling system

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-8335-2013 ◽

2013 ◽

Vol 13 (16) ◽

pp. 8335-8364 ◽

Cited By ~ 13

Author(s):

X.-Z. Liang ◽

F. Zhang

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Climate Modeling ◽

General Circulation Models ◽

Climate Impacts ◽

Sensitivity Analyses ◽

General Description ◽

Ensemble Modeling ◽

Uncertainty Range

Abstract. A cloud–aerosol–radiation (CAR) ensemble modeling system has been developed to incorporate the largest choices of alternate parameterizations for cloud properties (cover, water, radius, optics, geometry), aerosol properties (type, profile, optics), radiation transfers (solar, infrared), and their interactions. These schemes form the most comprehensive collection currently available in the literature, including those used by the world's leading general circulation models (GCMs). CAR provides a unique framework to determine (via intercomparison across all schemes), reduce (via optimized ensemble simulations), and attribute specific key factors for (via physical process sensitivity analyses) the model discrepancies and uncertainties in representing greenhouse gas, aerosol, and cloud radiative forcing effects. This study presents a general description of the CAR system and illustrates its capabilities for climate modeling applications, especially in the context of estimating climate sensitivity and uncertainty range caused by cloud–aerosol–radiation interactions. For demonstration purposes, the evaluation is based on several CAR standalone and coupled climate model experiments, each comparing a limited subset of the full system ensemble with up to 896 members. It is shown that the quantification of radiative forcings and climate impacts strongly depends on the choices of the cloud, aerosol, and radiation schemes. The prevailing schemes used in current GCMs are likely insufficient in variety and physically biased in a significant way. There exists large room for improvement by optimally combining radiation transfer with cloud property schemes.

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Robust Late 21st Century Shift in the Regional Monsoons in RegCM-CORDEX Simulations

10.5194/egusphere-egu2020-12102 ◽

2020 ◽

Author(s):

Moetasim Ashfaq ◽

Tereza Cavazos ◽

Michelle Reboita ◽

José Abraham Torres-Alavez ◽

Eun-Soon Im ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Regional Climate ◽

Lower Boundary ◽

Coupled Model ◽

General Circulation Models ◽

Monsoon Onset ◽

Historical Period ◽

Monsoon Period

<p>We use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas (GHG) forcing. All regional simulations are conducted using RegCM4 at a 25km horizontal grid spacing using lateral and lower boundary forcing from three General Circulation Models (GCMs), which are part of the fifth phase of the Coupled Model Inter-comparison Project (CMIP5). Each simulation covers the period from 1970 through 2100 under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Regional climate simulations exhibit high fidelity in capturing key characteristics of precipitation and atmospheric dynamics across monsoon regions in the historical period. In the future period, regional monsoons exhibit a spatially robust delay in the monsoon onset, an increase in seasonality, and a reduction in the rainy season length at higher levels of radiative forcing. All regions with substantial delays in the monsoon onset exhibit a decrease in pre-monsoon precipitation, indicating a strong connection between pre-monsoon drying and a shift in the monsoon onset. The weakening of latent heat driven atmospheric warming during the pre-monsoon period delays the overturning of atmospheric subsidence in the monsoon regions, which defers their transitioning into deep convective states. Monsoon changes under the RCP2.6 scenario are mostly within the baseline variability.&#160;</p>

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The global impact of supersaturation in a coupled chemistry-climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-1629-2007 ◽

2007 ◽

Vol 7 (6) ◽

pp. 1629-1643 ◽

Cited By ~ 25

Author(s):

A. Gettelman ◽

D. E. Kinnison

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

General Circulation Models ◽

Boreal Summer ◽

Boreal Winter ◽

Strong Impact ◽

Small Component ◽

Enhanced Production

Abstract. Ice supersaturation is important for understanding condensation in the upper troposphere. Many general circulation models however do not permit supersaturation. In this study, a coupled chemistry climate model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. Rather than a study of a detailed parameterization of supersaturation, the study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on climate and chemistry. High clouds decrease and water vapor in the stratosphere increases at a similar rate to the prescribed supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm−2) with a small component likely from the radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm−2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. There is no evidence of a strong impact of water vapor on tropical tropopause temperatures.

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Analysis of Cooling and Heating Degree Days over Mexico in Present and Future Climate

Atmosphere ◽

10.3390/atmos12091131 ◽

2021 ◽

Vol 12 (9) ◽

pp. 1131

Author(s):

Arturo Corrales-Suastegui ◽

Osias Ruiz-Alvarez ◽

José Abraham Torres-Alavez ◽

Edgar G. Pavia

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Regional Climate ◽

General Circulation Models ◽

Degree Days ◽

Heating And Cooling ◽

Heating Degree Days ◽

Near Future ◽

Far Future

One simple way to estimate the relationship between air temperature and the energy needed for heating and cooling is to use the concept of degree day. Cooling degree days (CDD) and heating degree days (HDD) are indicators of the energy required to reach comfort levels and are related directly to energy demands. Therefore, using a novel approach, we examine the current conditions and future projections in degree days over Mexico using observations (Livneh and CPC), ERA5 reanalysis, and simulations from the Regional Climate Model (RegCM4). The RegCM4 experiments were driven by different General Circulation Models for two Representative Concentration Pathways scenarios. We consider three 20-year periods as “present conditions” (1995–2014), “near-future conditions” (2041–2060), and “far-future conditions” (2080–2099). The results suggest that in the future, under the lowest radiative forcing scenario there will be a smaller increase (decrease) in CDD (HDD) for the far-future, as compared to the near-future. This could represent the model’s response to the peak of radiative forcing at mid-century and its subsequent decline. For the highest radiative forcing scenario, we found a greater increase (decrease) in CDD (HDD) for the far-future, which could be explained by the response of the RegCM4 to the warming increase projected for 2100.

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A new method for evaluating the impact of vertical distribution on aerosol radiative forcing in general circulation models

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-877-2014 ◽

2014 ◽

Vol 14 (2) ◽

pp. 877-897 ◽

Cited By ~ 23

Author(s):

M. R. Vuolo ◽

M. Schulz ◽

Y. Balkanski ◽

T. Takemura

Keyword(s):

Vertical Distribution ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Nonlinear Effects ◽

General Circulation Models ◽

Individual Species ◽

Aerosol Radiative Forcing ◽

Atmospheric Column ◽

The Impact

Abstract. The quantification and understanding of direct aerosol forcing is essential in the study of climate. One of the main issues that makes its quantification difficult is the lack of a complete understanding of the role of the vertical distribution of aerosols and clouds. This work aims at reducing the uncertainty of aerosol top-of-the-atmosphere (TOA) forcing due to the vertical superposition of several short-lived atmospheric components, in particular different aerosol species and clouds. We propose a method to quantify the contribution of different parts of the atmospheric column to the TOA forcing as well as to evaluate the contribution to model differences that is exclusively due to different spatial distributions of aerosols and clouds. We investigate the contribution of aerosol above, below and in clouds by using added diagnostics in the aerosol–climate model LMDz. We also compute the difference between the TOA forcing of the ensemble of the aerosols and the sum of the forcings from individual species in clear sky. This difference is found to be moderate for the global average (14%) but can reach high values regionally (up to 100%). Nonlinear effects are even more important when superposing aerosols and clouds. Four forcing computations are performed: one where the full aerosol 3-D distribution is used, and then three where aerosols are confined to regions above, inside and below clouds, respectively. We find that the TOA forcing of aerosols depends crucially on the presence of clouds and on their position relative to that of the aerosol, in particular for black carbon (BC). We observe a strong enhancement of the TOA forcing of BC above clouds, attenuation for BC below clouds, and a moderate enhancement when BC is found within clouds. BC above clouds accounts for only about 30% of the total BC optical depth but for 55% of the forcing, while forcing efficiency increases by a factor of 7.5 when passing from below to above clouds. The different behaviour of forcing nonlinearities for these three components of the atmospheric column encouraged us to develop the method for application to inter-model variability studies by reading 3-D aerosol and cloud fields from different general circulation models (GCMs) into the same model. We apply the method to the comparison of forcing due to the aerosols and clouds distributions of the general circulation models LMDz and SPRINTARS. The different amount of BC above but also within clouds is revealed to play a major role on the differences of cloudy-sky forcings between the two models, which can exceed 100% regionally.

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A new climate dataset for systematic assessments of climate change impacts as a function of global warming

Geoscientific Model Development ◽

10.5194/gmd-6-1689-2013 ◽

2013 ◽

Vol 6 (5) ◽

pp. 1689-1703 ◽

Cited By ~ 20

Author(s):

J. Heinke ◽

S. Ostberg ◽

S. Schaphoff ◽

K. Frieler ◽

C. Müller ◽

...

Keyword(s):

Climate Change ◽

Temperature Change ◽

General Circulation ◽

Climate Model ◽

Climate Change Impacts ◽

General Circulation Models ◽

Climate Change Scenarios ◽

Global Mean Temperature ◽

Mean Temperature ◽

Global Mean

Abstract. In the ongoing political debate on climate change, global mean temperature change (ΔTglob) has become the yardstick by which mitigation costs, impacts from unavoided climate change, and adaptation requirements are discussed. For a scientifically informed discourse along these lines, systematic assessments of climate change impacts as a function of ΔTglob are required. The current availability of climate change scenarios constrains this type of assessment to a narrow range of temperature change and/or a reduced ensemble of climate models. Here, a newly composed dataset of climate change scenarios is presented that addresses the specific requirements for global assessments of climate change impacts as a function of ΔTglob. A pattern-scaling approach is applied to extract generalised patterns of spatially explicit change in temperature, precipitation and cloudiness from 19 Atmosphere–Ocean General Circulation Models (AOGCMs). The patterns are combined with scenarios of global mean temperature increase obtained from the reduced-complexity climate model MAGICC6 to create climate scenarios covering warming levels from 1.5 to 5 degrees above pre-industrial levels around the year 2100. The patterns are shown to sufficiently maintain the original AOGCMs' climate change properties, even though they, necessarily, utilise a simplified relationships between ΔTglob and changes in local climate properties. The dataset (made available online upon final publication of this paper) facilitates systematic analyses of climate change impacts as it covers a wider and finer-spaced range of climate change scenarios than the original AOGCM simulations.

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The global impact of supersaturation in a coupled chemistry-climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-12433-2006 ◽

2006 ◽

Vol 6 (6) ◽

pp. 12433-12468 ◽

Cited By ~ 1

Author(s):

A. Gettelman ◽

D. E. Kinnison

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

General Circulation Models ◽

Boreal Summer ◽

Boreal Winter ◽

Strong Impact ◽

Small Component ◽

Enhanced Production

Abstract. Ice supersaturation is important for understanding condensation in the upper troposphere. Most general circulation models however do not permit supersaturation. In this study, a coupled chemistry climate model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. The study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on climate and chemistry. Results indicate that high clouds decrease and water vapor in the stratosphere increases nearly linearly with supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm−2) with a small component likely from radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm−2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. We do not see evidence of a strong impact of water vapor on tropical tropopause temperatures.

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Cloud-Aerosol-Radiation (CAR) ensemble modeling system

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-10193-2013 ◽

2013 ◽

Vol 13 (4) ◽

pp. 10193-10261 ◽

Cited By ~ 3

Author(s):

X.-Z. Liang ◽

F. Zhang

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Climate Modeling ◽

General Circulation Models ◽

Climate Impacts ◽

Sensitivity Analyses ◽

General Description ◽

Ensemble Modeling ◽

Uncertainty Range

Abstract. A Cloud-Aerosol-Radiation (CAR) ensemble modeling system has been developed to incorporate the largest choices of alternative parameterizations for cloud properties (cover, water, radius, optics, geometry), aerosol properties (type, profile, optics), radiation transfers (solar, infrared), and their interactions. These schemes form the most comprehensive collection currently available in the literature, including those used by the world leading general circulation models (GCMs). The CAR provides a unique framework to determine (via intercomparison across all schemes), reduce (via optimized ensemble simulations), and attribute specific key factors for (via physical process sensitivity analyses) the model discrepancies and uncertainties in representing greenhouse gas, aerosol and cloud radiative forcing effects. This study presents a general description of the CAR system and illustrates its capabilities for climate modeling applications, especially in the context of estimating climate sensitivity and uncertainty range caused by cloud-aerosol-radiation interactions. For demonstration purpose, the evaluation is based on several CAR standalone and coupled climate model experiments, each comparing a limited subset of the full system ensemble with up to 896 members. It is shown that the quantification of radiative forcings and climate impacts strongly depends on the choices of the cloud, aerosol and radiation schemes. The prevailing schemes used in current GCMs are likely insufficient in variety and physically biased in a significant way. There exists large room for improvement by optimally combining radiation transfer with cloud property schemes.

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