Current uncertainties inassessing aerosol effects on climate

The effect of anthropogenic emissions from activities, such as fossil-fuel, biomass, and biofuel burning; transportation; and land-clearing; have a profound impact on the climate system. The impact of these activities is manifested in observed changes in temperature, precipitation, sea-level rise, melting of glaciers, air quality, health, and agriculture yields, to name a few. The obvious question to ask is the role that these different processes play in affecting climate and what action could one impose to curtail or constrain adverse human impacts on climate. Greenhouse gases have long been studied, as they play a major role in changing climate. But over the past 10-20 years, aerosols have emerged as the other big contenders in climate change studies. This review focuses on the current understanding of the effects of aerosols on climate, with an emphasis on the thermodynamical and indirect aerosol effects. We also examine available measurements that could be used to decipher the aerosol influence on climate, with an outlook on how the uncertainties in aerosol effects may impact future climate predictions and policy changes.