Irrespective of future emission paths, in the next 20 years a several-fold increase in the frequency of unusually hot and extreme summer months can be expected from warming already underway says a report for the World Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics titled,'World Bank. 2013. Turn Down the Heat: Climate Extremes, Regional Impacts, and the Case for Resilience.
Losses induced by past droughts highlight current South Asian vulnerability to droughts according to the report. Of the 10 most severe drought disasters globally in the last century, measured in terms of the number of people affected, six took place in India; these affected up to 300 million people (in 1987 and 2002; 1900–2013 data based on EM-DAT 2013).
In the past few decades a warming trend has begun to emerge over South Asia, particularly in India, which appears to be consistent with the signal expected from human induced climate change. During recent decades, increases in the frequency of the most extreme precipitation events have been observed. Annual precipitation is projected to increase by up to 30 percent in a 4°C world. The seasonal distribution of precipitation is expected to become amplified, with a decrease of up to 30 percent during the dry season and a 30 percent increase during the wet season.
Temperature In a 4°C world
South Asian summer temperatures are projected to increase by 3°C to nearly 6°C by 2100, with the warming most pronounced in Pakistan. Under 4°C warming, the west coast and southern India, as well as Bhutan and northern Bangladesh, are projected to shift to new, high-temperature climatic regimes. Unusual heat is projected for 60–80 percent of the Northern Hemisphere summer months in most parts of the region.
Sea-level rise is projected to be approximately 100–115 cm by the 2090s in a 4°C world, and 60–80 cm in a 2°C world, by the end of the 21st century relative to 1986–2005. A substantial increase in excess mortality is expected to be associated with such heat extremes and has been observed in the past. Increasing risks and impacts from extreme river floods, more intense tropical cyclones, rising sea levels, and extraordinarily high temperatures are projected. Population displacement, which already periodically occurs in flood-prone areas, is likely to continue to result from severe flooding and other extreme events. Agricultural production is likely to suffer from the combined effects of rising temperatures, impacts on seasonal water availability, and the impacts of sea-level rise.
Large uncertainty remains about the behavior of the Indian summer monsoon under global warming, according to the analysis. An abrupt change in the monsoon, for example, toward a drier, lower rainfall state, could precipitate a major crisis in South Asia, as evidenced by the anomalous monsoon of 2002, which caused the most serious drought in recent times (with rainfall about 209 percent below the long-term normal and food grain production reductions of about 10–15 percent compared to the average of the preceding decade). Physically plausible mechanisms have been proposed for such a switch, and changes in the tropical atmosphere that could precipitate a transition of the monsoon to a drier state are projected in the present generation of climate models.
Across the whole warming range considered, there exists a significant relationship between crop yield decrease and temperature increase regardless of crop type. The impacts of climate change on food prices, agricultural yields, and production are expected to have direct implications for human well-being.