Abstract:Impacts of absorbing and scattering aerosols on global energy balance are investigated with a global climate model. A series of sensitivity experiments perturbing emissions of black carbon and sulfate aerosols individually is conducted with the model to explore how components of global energy budget change in response to the instantaneous radiative forcing due to the two types of aerosols. It is demonstrated how differing vertical structures of the instantaneous radiative forcing between the two aerosols induc… Show more
“…While there was no significant difference in the effective radiative forcing (Fig. 2 b), which is an index of rapid adjustment in the atmosphere, the differences in the surface air temperature increase at large reduction of anthropogenic SO 2 emissions depending on the CO 2 concentration were significant because the radiative imbalance due to sulphate aerosols results in mainly a slow climate response 17 . Figure 3 Sensitivity of surface air temperature to changes in SO 2 emissions.…”
It is generally believed that anthropogenic aerosols cool the atmosphere; therefore, they offset the global warming resulting from greenhouse gases to some extent. Reduction in sulphate, a primary anthropogenic aerosol, is necessary for mitigating air pollution, which causes atmospheric warming. Here, the changes in the surface air temperature under various anthropogenic emission amounts of sulphur dioxide (SO2), which is a precursor of sulphate aerosol, are simulated under both present and doubled carbon dioxide (CO2) concentrations with a climate model. No previous studies have conducted explicit experiments to estimate the temperature changes due to individual short-lived climate forcers (SLCFs) in different climate states with atmosphere–ocean coupled models. The simulation results clearly show that reducing SO2 emissions at high CO2 concentrations will significantly enhance atmospheric warming in comparison with that under the present CO2 concentration. In the high latitudes of the Northern Hemisphere, the temperature change that will occur when fuel SO2 emissions reach zero under a doubled CO2 concentration will be approximately 1.0 °C, while this value will be approximately 0.5 °C under the present state. This considerable difference can affect the discussion of the 1.5 °C/2 °C target in the Paris Agreement.
“…While there was no significant difference in the effective radiative forcing (Fig. 2 b), which is an index of rapid adjustment in the atmosphere, the differences in the surface air temperature increase at large reduction of anthropogenic SO 2 emissions depending on the CO 2 concentration were significant because the radiative imbalance due to sulphate aerosols results in mainly a slow climate response 17 . Figure 3 Sensitivity of surface air temperature to changes in SO 2 emissions.…”
It is generally believed that anthropogenic aerosols cool the atmosphere; therefore, they offset the global warming resulting from greenhouse gases to some extent. Reduction in sulphate, a primary anthropogenic aerosol, is necessary for mitigating air pollution, which causes atmospheric warming. Here, the changes in the surface air temperature under various anthropogenic emission amounts of sulphur dioxide (SO2), which is a precursor of sulphate aerosol, are simulated under both present and doubled carbon dioxide (CO2) concentrations with a climate model. No previous studies have conducted explicit experiments to estimate the temperature changes due to individual short-lived climate forcers (SLCFs) in different climate states with atmosphere–ocean coupled models. The simulation results clearly show that reducing SO2 emissions at high CO2 concentrations will significantly enhance atmospheric warming in comparison with that under the present CO2 concentration. In the high latitudes of the Northern Hemisphere, the temperature change that will occur when fuel SO2 emissions reach zero under a doubled CO2 concentration will be approximately 1.0 °C, while this value will be approximately 0.5 °C under the present state. This considerable difference can affect the discussion of the 1.5 °C/2 °C target in the Paris Agreement.
“…Decreased global-mean temperature further leads to reduced ARC PP from decreased atmospheric column temperature (i.e. Planck feedback) (Zelinka et al, 2020), and decreased water vapour content, which is controlled by the Clausius-Clapyron relationship (Suzuki and Takemura, 2019).…”
Changes in global-mean precipitation are strongly constrained by global radiative cooling, while regional rainfall changes are less constrained because energy can be transported. Absorbing and non-absorbing aerosols have different effects on both global-mean and regional precipitation, due to the distinct effects on energetics. This study analyses the precipitation responses to large perturbations in black carbon (BC) and sulphate (SUL) respectively by examining the changes in atmospheric energy budget terms on global and regional scales, in terms of fast (independent of changes in sea surface temperature (SST)) and slow responses (mediated by changes in SST). Changes in atmospheric radiative cooling/heating are further decomposed into contributions from clouds, aerosols, and clear-clean sky (without clouds or aerosols).Both cases show a decrease in global-mean precipitation, dominated by fast responses in the BC case while slow responses in the SUL case. The geographical patterns are distinct too. The intertropical convergence zone (ITCZ), accompanied with tropical rainfall, shifts northward in the BC case, while southward in the SUL case. For both cases, energy transport terms from the slow response dominates the changes in tropical rainfall, which are associated with the northward (southward) shift of Hadley cell in response to the enhanced southward (northward) cross-equatorial energy flux caused by increased BC (SUL) emission. The extra-tropical precipitation decreases in both cases. For the BC case, fast responses to increased atmospheric radiative heating contribute most to the reduced rainfall, in which absorbing aerosols directly heat the mid-troposphere, stabilise the column, and suppress precipitation. Unlike BC, non-absorbing aerosols decrease surface temperatures through slow processes, cool the whole atmospheric column, and reduce specific humidity, which leads to decreased radiative cooling from the clean-clear sky, and is consistent with the reduced rainfall. Examining the changes in large-scale circulation and local thermodynamics qualitatively explains the responses of precipitation to aerosol perturbations, whereas the energetic perspective provides a method to quantify their contributions.
“…The model experiments are those extended from the PDRMIP protocol, which increased BC and sulfur dioxide (SO2) emissions by ten times (x10) and five times (x5), respectively, relative to the present emission conditions (control experiment). In this study, the BC and Confidential manuscript submitted to SOLA 5 5 SO2 emissions are perturbed for their fuel sources by multiplying various globally uniform factors of 10, 5, 2, 1.5, 0.8, 0.5, 0.3, 0.1 and 0.0 to obtain more systematic and robust climate responses than PDRMIP (see Methods in Takemura and Suzuki, 2019) for these short-lived climate forcers with inhomogeneous spatial distributions. Simulations with increased solar insolation by +2% (denoted by Sol) and with CO2 concentration doubled (denoted by CO2) relative to the level in 2000 are also conducted but with no varying magnitudes for their relatively homogeneous nature.…”
Section: Model Experimentsmentioning
confidence: 99%
“…The results from PDRMIP highlight how AHS differs among forcing agents [Samset et al 2016] and how this difference is attributed to differing contributions from fast responses of energy budget components [Samset et al 2018;Richardson et al 2018]. The relative contributions from fast and slow responses are better understood in a whole picture of global energy budget [Suzuki and Takemura, 2019;hereafter ST19], which also explains 4 stark differences in global-mean responses of temperature [Takemura and Suzuki, 2019] and precipitation to BC and SF.…”
The apparent hydrological sensitivity, defined as the global-mean precipitation change per increase of the global-mean temperature, is investigated for scenarios induced by different forcing agents. Simulations with a climate model driven individually by four different climate forcers, i.e. sulfate, black carbon, solar insolation and carbon dioxide (CO2), are analyzed in the context of energy balance controls on global precipitation to explore how different forcing agents perturb different energy components grouped into fast and slow responses. Similarities and differences among the forcing agents are found in ingredients of the tendency contributing to the hydrological sensitivity from various energy budget components. Specifically, the sulfate and solar forcings induce the hydrological sensitivity of ~3.0%K-1 due to the slow response of radiative cooling whereas the black carbon induces a significantly negative hydrological sensitivity (~-Suzuki and Takemura, Hydrological Sensitivities due to Various Climate Forcers 2 6.0%K-1) due to the strong atmospheric heating. The CO2-induced hydrological sensitivity is found in between (~1.2%K-1) as a result from the slow response of radiative cooling and its partial compensation by the atmospheric heating. The findings provide a quantitative basis for interpreting climatic changes of global precipitation driven by a mixture of various natural and anthropogenic forcings.
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