While India’s population has been growing, its rice harvests have been declining. Two of the culprits, reports the BBC (citing a study from Proceedings of the National Academy of Sciences), are particulate and greenhouse-gas pollution.

South Asia suffers from a particularly nasty “brown cloud” – layers of pollution containing soot and other fine particles. The brown clouds reduce the amount of sunlight that reaches the crops, and polluted haze can also reduce rainfall. Researchers found that rice yields would have been higher under lower concentrations of greenhouse gases.

The BBC also reported on the related news that we’ll need to develop new crop strains adapted to a warmer future, or else face famine. According to the Consultative Group on International Agricultural Research (CGIAR), yields from existing varieties will fall, and crops once cultivated in poorer tropical countries will become viable in rich temperate countries.

BBC environmental correspondent Richard Black explains:

The most significant impact of climate change on agriculture is probably changes in rainfall. Some regions are forecast to receive more rain, others to receive less; above all, it will become more variable.

But increasing temperatures can also affect crops. Photosynthesis slows down as the thermometer rises, which also slows the plants’ growth and capacity to reproduce.

Research published two years ago shows rice yields are declining by 10% for every degree Celsius increase in night-time temperature.

A study from the International Maize and Wheat Improvement Center (Cimmyt) in Mexico, yet to be published, projects a major decline in South Asia’s wheat yield. The vast Indo-Gangetic plain produces about 15% of the world’s wheat – but the area suitable for growing is forecast to shrink by about half over the next 50 years, even as the number of mouths to feed increases.

CGIAR and affiliated groups are working to develop “climate-proof” varieties of rice, sorghum, and other grains that can survive floods or droughts and photosynthesize more efficiently.

They’re also helping farmers reduce the greenhouse gas emissions from their activities; for instance, minimum-till agriculture keeps carbon in the soil rather than letting it escape into the air as carbon dioxide.

So, while the president of the country that emits the most greenhouse gases claims that the science on global warming is still too uncertain to warrant action, poor countries are already having to adapt to the warmer climate.