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Clouds and aerosols provide the greatest uncertainty in estimating and interpreting Earth's energy budget. This study not only focuses on surface brightening/dimming, but also explores Earth's energy balance. The validation results of the CERES-SYN, ISCCP-FH, and GEWEX-SRB datasets with Baseline Surface Radiation Network (BSRN), Surface Radiation Budget Network (SURFRAD), and CMA observations show that CERES data have the highest accuracy and the longest temporal coverage. The role of clouds and aerosols in Earth's energy budget was explained using CERES and MERRA-2 products. The results show that Earth's energy increases at a rate of 0.63 W m−2 decade−1 in 2000–21. The global surface brightens at a rate of 0.57 W m−2 decade−1, with surface energy decreasing at a rate of 0.19 W m−2 decade−1. Brightening was found over Australia, central Asia, and southern Africa, mainly associated with cloud reduction, with aerosol emissions reductions contributing to the East Asian surface brightening. The surface brightening in South America and Southeast Asia is also due to the reduction of clouds. The increase of aerosols in South Asia is the main factor for its surface dimming, while we infer that the climatic effect from the increase of black carbon (BC) aerosols in South Asia is the inducing factor for the dimming in southern China. The surface darkening in West Asia is the result of the combined effect of clouds and aerosols, while in northern Africa it may be related to the increase of clouds caused by the decrease of dust aerosols. Surface energy increases only in Southeast Asia, South America, and Europe. Significance Statement: Clouds and aerosols provide the greatest uncertainty in estimating and interpreting Earth's changing energy budget. Moreover, the relative importance of clouds and aerosols is variable, depending on the regions and time scales of studies. This study shows that the energy inflow to the Earth system is greater than the energy outflow in 2000–21, with radiation on Earth increasing at a rate of 0.63 W m−2 decade−1 with the surface energy decreases at a rate of 0.19 W m−2 decade−1. Brightening was found over Southeast Asia, South America, Australia, and southern Africa, with the areas of surface darkening occurring mainly in Asia and northern Africa. [ABSTRACT FROM AUTHOR]

Fire emissions from the Maritime Continent (MC) over the western tropical Pacific are strongly influenced by El Niño–Southern Oscillation (ENSO), posing various climate effects to the Earth system. In this study, we show that the historical biomass burning emissions of black carbon (BCbb) aerosol in the dry season from the MC are strengthened in El Niño years due to the dry conditions. The eastern Pacific type of El Niño exerts a stronger modulation in BCbb emissions over the MC region than the central Pacific type of El Niño. Based on simulations using the fully coupled Community Earth System Model (CESM), the impacts of increased BCbb emissions on ENSO variability and frequency are also investigated in this study. With BCbb emissions from the MC scaled up by a factor of 10, which enables the identification of climate response from the internal variability, the increased BCbb heats the local atmosphere and changes land–sea thermal contrast, which suppresses the westward transport of the eastern Pacific surface water. It leads to an increase in sea surface temperature in the eastern tropical Pacific, which further enhances ENSO variability and increases the frequency of extreme El Niño and La Niña events. This study highlights the potential role of BCbb emissions on extreme ENSO frequency, and this role may be increasingly important in the warming future with higher wildfire risks. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosol particles in the Arctic heat the atmosphere and snow/ice surfaces and may strengthen the snow-albedo feedback that amplifies Arctic warming. Model simulations of BC concentrations in the Arctic depend strongly on the representation of microphysical processes such as aging, activation, and wet removal. Most BC modeling studies have classified BC particles into hydrophobic BC, which cannot form cloud droplets, and hydrophilic BC, which can form cloud droplets, by assuming a globally constant critical supersaturation threshold value (Sthre), without considering its consistency with cloud maximum supersaturation (Smax). Here we show that it is essential to consider the consistency of Sthre with Smax in global model simulations to reduce uncertainties in near-surface ambientBCconcentrations in the Arctic. Previous studies often obtained good agreement between simulated and observed near-surface Arctic BC mass concentrations when a low Sthre (;0.1%) was assumed in their models. However, this Sthre may be too low (activation and wet removal of BCmay be underestimated) for the Arctic, because some recent observations and our model simulations suggest that Smax may actually be higher (;0.3%) there. We also demonstrate that spatially varying Sthre values and their consistency with Smax, which previous studies did not consider, must be represented in models for more accurate estimation of BC budget in the Arctic. Because both Smax and BC-aging speed depend on climatic conditions, our findings are an important step toward better simulations of BC impacts on past, present, and future Arctic climates. [ABSTRACT FROM AUTHOR]

Studies of the climate effects of black carbon (BC) in East Asia are not abundant and the effects remain uncertain. Using the Community Earth System Model version 1 (CESM1) with Peking University's emissions data, the fast response of the atmospheric water cycle to anthropogenic BC during summer in East Asia is investigated in this study. Results show that the CESM1-simulated BC concentration and its direct effective radiative forcing are comparable to observations. With the combination of aerosol–radiation interaction (ARI) and non-aerosol–radiation interaction (including aerosol–cloud interaction and surface albedo effects), anthropogenic BC induces a "wetter south and drier north" pattern over East Asia during summer. Also, anthropogenic BC affects the summer precipitation primarily through changing moisture transport rather than altering local evaporation over East Asia. Using the self-developed atmospheric water tracer method, the responses of dominant moisture sources [the tropical Indian Ocean (TIO) and northwest Pacific] to anthropogenic BC are investigated. Results show that the moisture originating from southwest monsoon-related sources (especially the TIO) is more responsive to anthropogenic BC effects over East Asia. In particular, differing from total precipitation, TIO-supplied precipitation shows a significant response to the ARI of anthropogenic BC over East Asia. Process analyses show that anthropogenic BC affects the southwest monsoon-related moisture supplies primarily via advection, deep convection, and cloud macrophysics. Interestingly, the anthropogenic BC-induced changes of TIO-supplied water vapor in these three processes are all dominated by the ARI over East Asia. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosol is a significant and short-lived climate forcing factor. Here, the direct effects of BC emissions from India (IDBC) and China (CNBC) are investigated in East Asia during summer using the state-of-the-art regional climate model RegCM4. In summer, IDBC and CNBC account for approximately 30% and 46% of the total BC emissions in Asia, respectively. The total BC column burden from the two countries and corresponding TOA effective radiative forcing are 1.58 mgm-2 and 11.87Wm-2 in East Asia, respectively. The regional air temperature increases over 0.3K at maximum and precipitation decreases 0.028mmday-1 on average. Individually, IDBC and CNBC each can bring about rather different effects on regional climate. IDBC can result in a cooling perturbation accompanied by a substantially increased cloud amount and scattering aerosol loading, resulting in a complex response in the regional precipitation, while CNBC can lead to regional warming, and further induce a local flood in northern China or drought in southern China depending on the opposite but significant circulation anomalies. CNBC plays a dominant role in modulating the regional climate over East Asia due to its higher magnitude, wider coverage, and stronger climate feedback. The direct effect of the total BC from both countries is not a linear combination of that of IDBC and CNBC individually, suggesting that the regional climate responses are highly nonlinear to the emission intensity or aerosol loading, which may be greatly related to the influences of the perturbed atmospheric circulations and climate feedback. [ABSTRACT FROM AUTHOR]

The variability of the lower tropospheric temperature inversion (TI) across China remains poorly understood. Using seven years' worth of high-resolution radiosonde measurements at 120 sites, we compile the climatology of lower tropospheric TI in terms of frequency, intensity, and depth during the period from 2011 to 2017. The TI generally exhibits strong seasonal and geographic dependencies. Particularly, the TI frequency is found to be high in winter and low in summer, likely due to the strong aerosol radiative effect in winter. The frequency of the surface-based inversion (SBI) exhibits a ''west low, east high'' pattern at 0800 Beijing time (BJT), which then switches to ''west high, east low'' at 2000 BJT. Both the summertime SBI and elevated inversion (EI) reach a peak at 0800 BJT and a trough at 1400 BJT. Interestingly, the maximum wintertime EI frequency occurs over Southeast China (SEC) rather than over the North China Plain (NCP), likely attributable to the combination of the heating effect of black carbon (BC) originating from the NCP, along with the strong subsidence and trade inversion in SEC. Correlation analyses between local meteorology and TI indicate that larger lower tropospheric stability (LTS) favors more frequent and stronger TIs, whereas the stronger EI under smaller LTS conditions (unstable atmosphere) is more associated with subsidence rather than BC. Overall, the spatial pattern of the lower tropospheric TI and its variability in China are mainly controlled by three factors: local meteorology, large-scale subsidence, and BC-induced heating. These findings help shed some light on the magnitude, spatial distribution, and underlying mechanisms of the lower tropospheric TI variation in China. [ABSTRACT FROM AUTHOR]

Wildfires in the snow zone affect ablation by removing forest canopy, which enhances surface solar irradiance, and depositing light absorbing particles [LAPs, such as black carbon (BC)] on the snowpack, reducing snow albedo. How variations in BC deposition affects post-wildfire snowmelt timing is poorly known and highly relevant to water resources. We present a field-based analysis of BC variability across five sites of varying burn age and burn severity in the Cascade Range, Washington State, United States. Single particle soot photometer (SP2) analyses of BC snow concentrations were used to assess the impact of BC on snow albedo, and radiative transfer modeling was used to estimate the radiative effect of BC on snowmelt. Results were compared to Snowpack Telemetry (SNOTEL) data from one site that burned in 2012 and another in a proximal unburned forest. We show that post-wildfire forests provide a significant source of BC to the snowpack, and this effect increases by an order of magnitude in regions of high versus low burn severity, and decreased by two orders of magnitude over a decade. There is a shift in the timing of snowmelt, with snow disappearance occurring on average 196 9 days earlier post-wildfire (2013-19) relative to pre-wildfire (1983-2012). This study improves understanding of the connection between wildfire activity and snowmelt, which is of high relevance as climate change models project further decreases in snowpack and increases in wildfire activity in the Washington Cascades. [ABSTRACT FROM AUTHOR]

An obvious warming trend in winter over the Tibetan Plateau (TP) in the recent decades has been widely discussed, with studies emphasizing the dominant effects of local radiative factors, including those due to black carbon (BC). The Himalayas are one of the largest snowpack- and ice-covered regions in the TP, and an ideal area to investigate local radiative effects on climate change. In this study, the coupled climate feedback response analysis method (CFRAM) is applied to quantify the magnitude of warming over the Himalayas induced by different external forcing factors and climate feedback processes. The results show that snow/ice albedo feedback (SAF) resulted in a warming of approximately 2.6°C and was the primary contributor to enhanced warming over the Himalayas in recent decades. This warming was much greater than the warming induced by dynamic and other radiative factors. In particular, the strong radiative effects of BC on the warming over the Himalayas are identified by comparing control and BC-perturbed experiments of the Community Earth System Model (CESM). As a result of strong BC effects on the Himalayas, evaporation and reduced precipitation were strengthened, accounting for local drying and land degradation, which intensified warming. These results suggest that more investigations on the local radiative effects on the climate and ecosystem are needed, especially in the high-altitude cryosphere. [ABSTRACT FROM AUTHOR]

This study explores the effects of black carbon (BC) and sulfate (SO4) on global and tropical precipitation with a climate model. Results show that BC causes a decrease in global annual mean precipitation, consisting of a large negative tendency of a fast precipitation response scaling with instantaneous atmospheric absorption and a small positive tendency of a slow precipitation response scaling with the BC-caused global warming. SO4 also causes a decrease in global annual mean precipitation, which is dominated by a slow precipitation response corresponding to the surface cooling caused by SO4. BC causes a northward shift of the intertropical convergence zone (ITCZ), mainly through a fast precipitation response, whereas SO4 causes a southward shift of the ITCZ through a slow precipitation response. The displacements of the ITCZ caused by BC and SO4 are found to linearly correlate with the corresponding changes in cross-equatorial heat transport in the atmosphere, with a regression coefficient of about −3° PW−1, implying that the ITCZ shifts occur as manifestations of the atmospheric cross-equatorial heat transport changes in response to the BC and SO4 forcings. The atmospheric cross-equatorial heat transport anomaly caused by BC is basically driven by the BC-induced interhemispheric contrast in instantaneous atmospheric absorption, whereas the atmospheric cross-equatorial heat transport anomaly caused by SO4 is mostly attributable to the response of evaporation. It is found that a slab-ocean model exaggerates the cross-equatorial heat transport response in the atmosphere and the ITCZ shift both for BC and SO4, as compared with an ocean-coupled model. This underscores the importance of using an ocean-coupled model in modeling studies of the tropical climate response to aerosols. [ABSTRACT FROM AUTHOR]

Calculations of the radiative properties of hydrated ammonium sulfate (AS) aerosols often employ the conventional volume mixing rule, in which the refractive indices of AS and water are linearly averaged, weighted by their respective volume fractions in solution, and the real part of the refractive index of pure AS is taken to be 1.52-1.55, based on measurements of dry crystalline AS. However, there are significant differences between the refractive indices of AS-water solutions calculated using the conventional volume mixing rule and empirically derived refractive indices. The authors use a simple model for calculating the direct solar radiative forcing efficiency (RFE; radiative forcing divided by optical depth) of an optically thin layer of aerosols to investigate the magnitude of these differences. The difference between the conventional volume mixing rule and empirically derived refractive indices amounts to a modest difference in the direct solar RFE of AS aerosols at the top of the atmosphere at 0.550- μm wavelength and at relative humidities of 37%%-99.9%%. Without black carbon, the difference in RFE is up to −0.42 W m−2 for relative humidities less than around 66%% and up to 0.25 W m−2 for relative humidities greater than 66%%, whereas with 2%% black carbon by volume, the range of difference in RFE is up to −0.59 W m−2 for relative humidities less than 66%% and up to 0.30 W m−2 for relative humidities greater than 66%%. Although modest, this difference in RFE may become important when investigating regional aerosol forcing in areas with a high concentration of urban and industrial pollution. [ABSTRACT FROM AUTHOR]