| The climatic effects of aerosols, either through their optical properties or through changing the properties of clouds, have drawn lots of attention worldwide. But aerosols are still the largest uncertainty in the study of anthropogenic driving climate change up to now, because most of their processes interacted with clouds are far from understood. The traditional conceptual framework of radiative forcing is neither in favor of reducing the relevant uncertainties nor beneficial for predicting long-term climate change in practice. Therefore, an effective radiative forcing (ERF), as newly defined by IPCC AR5 was adopted in discussing the radiative forcing of anthropogenic aerosols, using an aerosol-climate coupled model system BCC AGCM2.0.1 CUACE/Aero from National Climate Center of China, which have included aerosol-cloud interacting module. Besides discussing the effects of aerosols on temperature, clouds, circulation and precipitation like most other studies, we went forward to discuss the effects of aerosols on global terrestrial aridity and the dimensions of arid and semi-arid areas. Key conclusions are as follows:(1)From 1850-2010, the ERF of total anthropogenic aerosols was-2.49 W m-2, of which the aerosol-radiation interactive ERF (ERFari) and aerosol-cloud interactive ERF (ERFaci) were-0.30 and-2.19 W m-2, respectively. The ERF of sulfate (SF), black carbon (BC), and organic aerosols (OA) were-2.37,0.12, and -0.31 W m-2, respectively. From 1850-2010, anthropogenic aerosols led to a decrease of 2.53 K and 0.20 mm day-1 in global annual mean temperature and precipitation, respectively. From 2010-2100 (based on IPCC RCP4.5), anthropogenic aerosols brought about an increase of 2.06 K and 0.16 mm day-1 in global annual mean temperature and precipitation, respectively. Temperature response caused by anthropogenic aerosols was most obvious over mid and high latitudes in the northern hemisphere, and the precipitation center of ITCZ tended to shift towards the relative warmer hemisphere.(2)From 1850-2010, total anthropogenic aerosols led to a decrease of 0.18 and 0.35 mm day-1 in land mean precipitation and reference evapotranspiration (ET0, the power of evaporation and transpiration), respectively, which meant that total anthropogenic aerosols depressed the water demand more than water supply over land, thus would not lead to an increase in terrestrial aridity or expansion of arid and semi-arid areas, from a global perspective. But total anthropogenic aerosols would increase the terrestrial aridity and the dimensions of arid and semi-arid areas over East Asia, South Asia, and North America, highlighting the importance of anthropogenic aerosols mitigation over these areas.(3)Among three anthropogenic aerosols, SF was the most important in affecting terrestrial aridity and the boundaries of arid and semi-arid areas. SF and OA could depress ETo through reducing surface temperature, decreasing surface available energy, and increasing surface air relative humidity, thus would not lead to an increase in terrestrial aridity or expansion of arid and semi-arid areas, from a global perspective. But they might cause the arid and semi-arid areas over North Africa shift southward and the arid and semi-arid areas over East and South Asia to expand. BC could increase surface temperature, and decrease surface available energy at the same time. So, the effect of BC on ET0 was determined by the comparison of the contributions of the above two variables. BC might lead to an expansion of the total arid and semi-arid areas.(4)Dust is a kind of natural aerosol, which has close relations with arid climate. Dust are mainly emitted from arid and semi-arid areas, and affects the climate of arid and semi-arid areas in reverse. As a scattering aerosol, dust could reduce ETo more obvious than precipitation, thus had a negative feedback to arid climate. But unlike SF and OA, dust aerosols depressed land mean ETo mainly through decreasing surface available energy. |
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