Climate change and the South Asian summer monsoon

In spite of the rise in atmospheric CO₂ concentration of about 70 parts per million by volume and in global temperatures of about 0.50°C over the last 6 decades, the All India Rainfall index does not yet show the expected increase in rainfall. The reviewers Andrew Turner from the Department of Meteorology at the University of Reading and H. Annamalai from the International Pacific Research Center at the University of Hawaii at Manoa give several reasons for why the region's observed rainfall has not yet increased, among them are inconsistent rainfall observations, decadal variability of the monsoon, the effects of aerosols resulting from industrialization, and land-use changes.

Regional projections for devastating droughts and floods--which are most meaningful for residents living in South Asia-- are still beyond the reach of current climate models, according to the reviewers' detailed analyses of the present state of research. The authors conclude that in order to make regional projections that can help in disaster mitigation and in adapting to climate change, the following is needed: establishing more consistent rainfall datasets by expanding observations to include, for example, agricultural yield; a better grasp of the complicated thermodynamics over the monsoon region and of the interactions among monsoon rainfall, land-use, aerosols, CO₂, and other conditions; and an evaluation in coupled circulation models (which allow feedbacks among variables) of those processes that have been shown in simpler models to affect the monsoon and rainfall.