Aerosols heat up
Aerosols are thought to have a cooling effect on the atmosphere, and therefore to have mitigated some of the expected global warming over this period. This is, however, a highly uncertain conclusion, in part because the total amount and vertical distribution of solar radiation that is absorbed by aerosol particles is imperfectly known. There was an interesting article in Nature (Vol-448, 2 August 2007) under “News and Views” by Prof. Peter Pilewskie. In the same issue, Ramanathan et al. (on page 575) report that the aerosol clouds above large regions of Asia actually cause as much warming as greenhouse gases — in contradiction, at first glance, to the notion of aerosol particles as a cooling agent.
Figure 1. Smog drifts down India's populous Ganges valley and out into the Bay of Bengal. This is the source of 'atmospheric brown clouds' over the Indian Ocean, and the climatic effect of its constituent aerosol particles is investigated by Ramanathan and colleagues
For more information and understanding, please refer following two articles and references therein:
Pilewskie, P., 2007, Aerosols heat up, Nature 448, 541-542.
Ramanathan et al. 2007, Warming trends in Asia amplified by brown cloud solar absorption, Nature 448, 575-578.