Heat waves in India during the pre-monsoon months have significant impacts on human health, productivity and mortality. While greenhouse gas-induced global warming is believed to accentuate high temperature extremes, anthropogenic aerosols predominantly constituted by radiation-scattering sulfate are believed to cause an overall cooling in most world regions. However, the Indian region is marked by an abundance of absorbing aerosols, such as black carbon (BC) and dust. The goal of this work was to understand the association between aerosols, particularly those that are absorbing in nature, and high-temperature extremes in north-central India during the pre-monsoon season. We use 30-year simulations from a chemistry-coupled atmosphere-only general circulation model (GCM), ECHAM6-HAM2, forced with evolving aerosol emissions in an interactive aerosol module, along with observed evolving SSTs. A composite of high-temperature extremes in the model simulations, compared to climatology, shows large-scale conditions conducive to heat waves. Importantly, it reveals concurrent positive anomalies of BC and dust aerosol optical depths. Changes in near-surface properties include a reduction in single scattering albedo (implying greater absorption) and enhancement in short-wave heating rate, compared to climatological conditions. Alterations in surface energy balance include reduced latent heat flux, but increased sensible heat flux, consistent with enhanced temperatures. Thus, chemistry-coupled GCM simulations capture an association of absorbing aerosols with high-temperature extremes in north India, arising from radiative heating in the surface layer.

We used an online aerosol-climate model (BCC_AGCM2.0_CUACE/Aero) to simulate effective radiative forcing and climate response to changes in the concentrations of short-lived climatic pollutants (SLCPs), including methane, tropospheric ozone, and black carbon, for the period 2010-2050 under Representative Concentration Pathway scenarios (RCPs) 8.5, 4.5, and 2.6. Under these three scenarios, the global annual mean effective radiative forcing were 0.1, -0.3, and -0.5Wm(-2), respectively. Under RCP 8.5, the change in SLCPs caused significant increases in surface air temperature (SAT) in middle and high latitudes of the Northern Hemisphere and significant decreases in precipitation in the Indian Peninsula and equatorial Pacific. Global mean SAT and precipitation increased by 0.13K and 0.02 mmd(-1), respectively. The reduction in SLCPs from 2010 to 2050 under RCPs 4.5 and 2.6 led to significant decreases in SAT at high latitudes in the Northern Hemisphere. Precipitation increased slightly in most continental regions, and the Intertropical Convergence Zone moved southward under both of these mitigation scenarios. Global mean SAT decreased by 0.20 and 0.44K, and global averaged precipitation decreased by 0.02 and 0.03 mmd(-1) under RCPs 4.5 and 2.6, respectively.

This study simulates the effective radiative forcing (ERF) of tropospheric ozone from 1850 to 2013 and its effects on global climate using an aerosol-climate coupled model, BCC AGCM2.0.1 CUACE/Aero, in combination with OMI (Ozone Monitoring Instrument) satellite ozone data. According to the OMI observations, the global annual mean tropospheric column ozone (TCO) was 33.9 DU in 2013, and the largest TCO was distributed in the belts between 30A degrees N and 45A degrees N and at approximately 30A degrees S; the annual mean TCO was higher in the Northern Hemisphere than that in the Southern Hemisphere; and in boreal summer and autumn, the global mean TCO was higher than in winter and spring. The simulated ERF due to the change in tropospheric ozone concentration from 1850 to 2013 was 0.46 W m(-2), thereby causing an increase in the global annual mean surface temperature by 0.36A degrees C, and precipitation by 0.02 mm d(-1) (the increase of surface temperature had a significance level above 95%). The surface temperature was increased more obviously over the high latitudes in both hemispheres, with the maximum exceeding 1.4A degrees C in Siberia. There were opposite changes in precipitation near the equator, with an increase of 0.5 mm d(-1) near the Hawaiian Islands and a decrease of about -0.6 mm d(-1) near the middle of the Indian Ocean.

An interactive system coupling the Beijing Climate Center atmospheric general circulation model (BCC_AGCM2.0.1) and the Canadian Aerosol Module (CAM) with updated aerosol emission sources was developed to investigate the global distributions of optical properties and direct radiative forcing (DRF) of typical aerosols and their impacts on East Asian climate. The simulated total aerosol optical depth (AOD), single scattering albedo, and asymmetry parameter were generally consistent with the ground-based measurements. Under all-sky conditions, the simulated global annual mean DRF at the top of the atmosphere was -2.03 W m(-2) for all aerosols including sulfate, organic carbon (OC), black carbon (BC), dust, and sea salt; the global annual mean DRF was -0.23 W m(-2) for sulfate, BC, and OC aerosols. The sulfate, BC, and OC aerosols led to decreases of 0.58 degrees and 0.14 mm day(-1) in the JJA means of surface temperature and precipitation rate in East Asia. The differences of land-sea surface temperature and surface pressure were reduced in East Asian monsoon region due to these aerosols, thus leading to the weakening of East Asian summer monsoon. Atmospheric dynamic and thermodynamic were affected due to the three types of aerosol, and the southward motion between 15 degrees N and 30 degrees N in lower troposphere was increased, which slowed down the northward transport of moist air carried by the East Asian summer monsoon, and moreover decreased the summer monsoon precipitation in south and east China.