An updated estimation of radiative forcing due to CO2 and its effect on global surface temperature change

Abstract Previous work has demonstrated that observed and modeled climates show a near-time-invariant ratio of mean land to mean ocean surface temperature change under transient and equilibrium global warming. This study confirms this in a range of atmospheric models coupled to perturbed sea surface temperatures (SSTs), slab (thermodynamics only) oceans, and a fully coupled ocean. Away from equilibrium, it is found that the atmospheric processes that maintain the ratio cause a land-to-ocean heat transport anomaly that can be approximated using a two-box energy balance model. When climate is forced by increasing atmospheric CO2 concentration, the heat transport anomaly moves heat from land to ocean, constraining the land to warm in step with the ocean surface, despite the small heat capacity of the land. The heat transport anomaly is strongly related to the top-of-atmosphere radiative flux imbalance, and hence it tends to a small value as equilibrium is approached. In contrast, when climate is forced by prescribing changes in SSTs, the heat transport anomaly replaces “missing” radiative forcing over land by moving heat from ocean to land, warming the land surface. The heat transport anomaly remains substantial in steady state. These results are consistent with earlier studies that found that both land and ocean surface temperature changes may be approximated as local responses to global mean radiative forcing. The modeled heat transport anomaly has large impacts on surface heat fluxes but small impacts on precipitation, circulation, and cloud radiative forcing compared with the impacts of surface temperature change. No substantial nonlinearities are found in these atmospheric variables when the effects of forcing and surface temperature change are added.

Download Full-text

Transient climate and ambient health impacts due to national solid fuel cookstove emissions

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1612430114 ◽

2017 ◽

Vol 114 (6) ◽

pp. 1269-1274 ◽

Cited By ~ 50

Author(s):

Forrest G. Lacey ◽

Daven K. Henze ◽

Colin J. Lee ◽

Aaron van Donkelaar ◽

Randall V. Martin

Keyword(s):

Surface Temperature ◽

Solid Fuel ◽

Ambient Air ◽

Atmospheric Modeling ◽

Ambient Air Pollution ◽

Health Impacts ◽

Surface Temperature Change ◽

Global Surface Temperature ◽

Premature Deaths ◽

Global Surface

Residential solid fuel use contributes to degraded indoor and ambient air quality and may affect global surface temperature. However, the potential for national-scale cookstove intervention programs to mitigate the latter issues is not yet well known, owing to the spatial heterogeneity of aerosol emissions and impacts, along with coemitted species. Here we use a combination of atmospheric modeling, remote sensing, and adjoint sensitivity analysis to individually evaluate consequences of a 20-y linear phase-out of cookstove emissions in each country with greater than 5% of the population using solid fuel for cooking. Emissions reductions in China, India, and Ethiopia contribute to the largest global surface temperature change in 2050 [combined impact of −37 mK (11 mK to −85 mK)], whereas interventions in countries less commonly targeted for cookstove mitigation such as Azerbaijan, Ukraine, and Kazakhstan have the largest per cookstove climate benefits. Abatement in China, India, and Bangladesh contributes to the largest reduction of premature deaths from ambient air pollution, preventing 198,000 (102,000–204,000) of the 260,000 (137,000–268,000) global annual avoided deaths in 2050, whereas again emissions in Ukraine and Azerbaijan have the largest per cookstove impacts, along with Romania. Global cookstove emissions abatement results in an average surface temperature cooling of −77 mK (20 mK to −278 mK) in 2050, which increases to −118 mK (−11 mK to −335 mK) by 2100 due to delayed CO2 response. Health impacts owing to changes in ambient particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) amount to ∼22.5 million premature deaths prevented between 2000 and 2100.

Download Full-text

The Dependence of Radiative Forcing and Feedback on Evolving Patterns of Surface Temperature Change in Climate Models

Journal of Climate ◽

10.1175/jcli-d-14-00545.1 ◽

2015 ◽

Vol 28 (4) ◽

pp. 1630-1648 ◽

Cited By ~ 159

Author(s):

Timothy Andrews ◽

Jonathan M. Gregory ◽

Mark J. Webb

Keyword(s):

Surface Temperature ◽

Temperature Change ◽

Radiative Forcing ◽

General Circulation ◽

Climate Feedback ◽

Climate Feedbacks ◽

Surface Temperature Change ◽

Feedback Parameter ◽

Surface Warming ◽

Global Mean

Abstract Experiments with CO2 instantaneously quadrupled and then held constant are used to show that the relationship between the global-mean net heat input to the climate system and the global-mean surface air temperature change is nonlinear in phase 5 of the Coupled Model Intercomparison Project (CMIP5) atmosphere–ocean general circulation models (AOGCMs). The nonlinearity is shown to arise from a change in strength of climate feedbacks driven by an evolving pattern of surface warming. In 23 out of the 27 AOGCMs examined, the climate feedback parameter becomes significantly (95% confidence) less negative (i.e., the effective climate sensitivity increases) as time passes. Cloud feedback parameters show the largest changes. In the AOGCM mean, approximately 60% of the change in feedback parameter comes from the tropics (30°N–30°S). An important region involved is the tropical Pacific, where the surface warming intensifies in the east after a few decades. The dependence of climate feedbacks on an evolving pattern of surface warming is confirmed using the HadGEM2 and HadCM3 atmosphere GCMs (AGCMs). With monthly evolving sea surface temperatures and sea ice prescribed from its AOGCM counterpart, each AGCM reproduces the time-varying feedbacks, but when a fixed pattern of warming is prescribed the radiative response is linear with global temperature change or nearly so. It is also demonstrated that the regression and fixed-SST methods for evaluating effective radiative forcing are in principle different, because rapid SST adjustment when CO2 is changed can produce a pattern of surface temperature change with zero global mean but nonzero change in net radiation at the top of the atmosphere (~−0.5 W m−2 in HadCM3).

Download Full-text

Strong modification of stratospheric ozone forcing by cloud and sea ice adjustments

10.5194/acp-2016-175 ◽

2016 ◽

Author(s):

Y. Xia ◽

Y. Hu ◽

Y. Huang

Keyword(s):

Sea Ice ◽

Surface Temperature ◽

Temperature Change ◽

Radiative Forcing ◽

Stratospheric Ozone ◽

Climatic Impact ◽

Surface Cooling ◽

Surface Temperature Change ◽

Surface Warming ◽

Climate Simulations

Abstract. We investigate the climatic impact of stratospheric ozone recovery (SOR) with a focus on the surface temperature change in atmosphere-slab-ocean coupled climate simulations. We find that although SOR would cause significant surface warming (global mean: 0.2 K) in a climate free of clouds and sea-ice, it may result in surface cooling (−0.06 K) in the real climate. The results here are especially interesting in that the stratosphere-adjusted radiative forcing is positive in both cases. Radiation diagnosis shows that the surface cooling is mainly due to a strong radiative effect resulting from significant reduction of global high clouds and, to a lesser extent, from an increase in high-latitude sea ice. Our simulation experiments suggest clouds and sea ice are sensitive to stratospheric ozone perturbation, which constitutes a significant radiative adjustment that influences the sign and magnitude of the global surface temperature change.

Download Full-text

The effect of rapid adjustments to halocarbons and N2O on radiative forcing

npj Climate and Atmospheric Science ◽

10.1038/s41612-020-00150-x ◽

2020 ◽

Vol 3 (1) ◽

Author(s):

Øivind Hodnebrog ◽

Gunnar Myhre ◽

Ryan J. Kramer ◽

Keith P. Shine ◽

Timothy Andrews ◽

...

Keyword(s):

Surface Temperature ◽

Temperature Change ◽

Radiative Forcing ◽

Climate Models ◽

Global Climate ◽

Initial Perturbation ◽

Global Climate Models ◽

Radiative Heating ◽

Surface Temperature Change ◽

Precipitation Decrease

AbstractRapid adjustments occur after initial perturbation of an external climate driver (e.g., CO2) and involve changes in, e.g. atmospheric temperature, water vapour and clouds, independent of sea surface temperature changes. Knowledge of such adjustments is necessary to estimate effective radiative forcing (ERF), a useful indicator of surface temperature change, and to understand global precipitation changes due to different drivers. Yet, rapid adjustments have not previously been analysed in any detail for certain compounds, including halocarbons and N2O. Here we use several global climate models combined with radiative kernel calculations to show that individual rapid adjustment terms due to CFC-11, CFC-12 and N2O are substantial, but that the resulting flux changes approximately cancel at the top-of-atmosphere due to compensating effects. Our results further indicate that radiative forcing (which includes stratospheric temperature adjustment) is a reasonable approximation for ERF. These CFCs lead to a larger increase in precipitation per kelvin surface temperature change (2.2 ± 0.3% K−1) compared to other well-mixed greenhouse gases (1.4 ± 0.3% K−1 for CO2). This is largely due to rapid upper tropospheric warming and cloud adjustments, which lead to enhanced atmospheric radiative cooling (and hence a precipitation increase) and partly compensate increased atmospheric radiative heating (i.e. which is associated with a precipitation decrease) from the instantaneous perturbation.

Download Full-text

Metrics for linking emissions of gases and aerosols to global precipitation changes

Earth System Dynamics ◽

10.5194/esd-6-525-2015 ◽

2015 ◽

Vol 6 (2) ◽

pp. 525-540 ◽

Cited By ~ 16

Author(s):

K. P. Shine ◽

R. P. Allan ◽

W. J. Collins ◽

J. S. Fuglestvedt

Keyword(s):

Surface Temperature ◽

Temperature Change ◽

Radiative Forcing ◽

Precipitation Change ◽

Pulse Emission ◽

Surface Temperature Change ◽

Input Parameters ◽

Global Temperature Change ◽

Precipitation Changes ◽

Global Precipitation

Abstract. Recent advances in understanding have made it possible to relate global precipitation changes directly to emissions of particular gases and aerosols that influence climate. Using these advances, new indices are developed here called the Global Precipitation-change Potential for pulse (GPPP) and sustained (GPPS) emissions, which measure the precipitation change per unit mass of emissions. The GPP can be used as a metric to compare the effects of different emissions. This is akin to the global warming potential (GWP) and the global temperature-change potential (GTP) which are used to place emissions on a common scale. Hence the GPP provides an additional perspective of the relative or absolute effects of emissions. It is however recognised that precipitation changes are predicted to be highly variable in size and sign between different regions and this limits the usefulness of a purely global metric. The GPPP and GPPS formulation consists of two terms, one dependent on the surface temperature change and the other dependent on the atmospheric component of the radiative forcing. For some forcing agents, and notably for CO2, these two terms oppose each other – as the forcing and temperature perturbations have different timescales, even the sign of the absolute GPPP and GPPS varies with time, and the opposing terms can make values sensitive to uncertainties in input parameters. This makes the choice of CO2 as a reference gas problematic, especially for the GPPS at time horizons less than about 60 years. In addition, few studies have presented results for the surface/atmosphere partitioning of different forcings, leading to more uncertainty in quantifying the GPP than the GWP or GTP. Values of the GPPP and GPPS for five long- and short-lived forcing agents (CO2, CH4, N2O, sulphate and black carbon – BC) are presented, using illustrative values of required parameters. The resulting precipitation changes are given as the change at a specific time horizon (and hence they are end-point metrics) but it is noted that the GPPS can also be interpreted as the time-integrated effect of a pulse emission. Using CO2 as a references gas, the GPPP and GPPS for the non-CO2 species are larger than the corresponding GTP values. For BC emissions, the atmospheric forcing is sufficiently strong that the GPPS is opposite in sign to the GPPS. The sensitivity of these values to a number of input parameters is explored. The GPP can also be used to evaluate the contribution of different emissions to precipitation change during or after a period of emissions. As an illustration, the precipitation changes resulting from emissions in 2008 (using the GPPP) and emissions sustained at 2008 levels (using the GPPS) are presented. These indicate that for periods of 20 years (after the 2008 emissions) and 50 years (for sustained emissions at 2008 levels) methane is the dominant driver of positive precipitation changes due to those emissions. For sustained emissions, the sum of the effect of the five species included here does not become positive until after 50 years, by which time the global surface temperature increase exceeds 1 K.

Download Full-text

A Temporal Kernel Method to Compute Effective Radiative Forcing in CMIP5 Transient Simulations*

Journal of Climate ◽

10.1175/jcli-d-15-0577.1 ◽

2016 ◽

Vol 29 (4) ◽

pp. 1497-1509 ◽

Cited By ~ 13

Author(s):

Erik J. L. Larson ◽

Robert W. Portmann

Keyword(s):

Surface Temperature ◽

Temperature Change ◽

Radiative Forcing ◽

Kernel Method ◽

Coupled Model ◽

Volcanic Eruptions ◽

Atmospheric Temperature ◽

Surface Temperature Change ◽

Effective Radiative Forcing ◽

The Difference

Abstract Effective radiative forcing (ERF) is calculated as the flux change at the top of the atmosphere after allowing rapid adjustments resulting from a forcing agent, such as greenhouse gases. Rapid adjustments include changes to atmospheric temperature, water vapor, and clouds. Accurate estimates of ERF are necessary in order to understand the drivers of climate change. This work presents a new method of calculating ERF using a kernel derived from the time series of a model variable (e.g., global mean surface temperature) in a model-step change experiment. The top-of-atmosphere (TOA) radiative imbalance has the best noise tolerance for retrieving the ERF of the model variables tested. This temporal kernel method is compared with an energy balance method, which equates ERF to the TOA radiative imbalance plus the scaled surface temperature change. Sensitivities and biases of these methods are quantified using output from phase 5 of the the Coupled Model Intercomparison Project (CMIP5). The temporal kernel method is likely more accurate for models in which a linear fit is a poor approximation for the relationship between temperature change and TOA imbalance. The difference between these methods is most apparent in forcing estimates for the representative concentration pathway 8.5 (RCP8.5) scenario. The CMIP5 multimodel mean ERF calculated for large volcanic eruptions is 80% of the adjusted forcing reported by the IPCC Fifth Assessment Report (AR5). This suggests that about 5% more energy has come into the earth system since 1870 than suggested by the IPCC AR5.

Download Full-text