The complexity of climate systems makes forecasting the monsoon tough. It is erratic anyway: four years in every ten, it is abnormal. Furthermore, humans are changing the environment. Clearing forest and vegetation means less water is stored in the land, for example. Air pollution is a huge problem, too, much of it caused by cooking at home. The polluting aerosols, such as black carbon, released by this and other activities interact with sunlight. Some of these tiny particles—many less than one tenth of the width of a human hair—scatter it, while others absorb it. Both effects alter the heating of the atmospheric column, and thus the heating of the land relative to the ocean—a phenomenon which helps drive the monsoon.
The heat trapped by greenhouse gases is likely to lead to even greater variability in the monsoon. Rainfall extremes are expected to increase, thanks partly to the fact that a warmer atmosphere can hold more moisture (about 7% more for every 1°C of warming). And the world is sweltering. This year is almost certain to be the hottest ever recorded; 370 months in a row have now been either warm or warmer-than-average, according to the World Meteorological Organisation, a UN agency.