India’s first ever national forecast on the impact of global warming on the subcontinent in the coming century, expects annual rainfall to increase, along with more severe cyclones and — paradoxically — more droughts.
These projections, based on a climate forecasting model developed at the Indian Institute of Tropical Meteorology (IITM), Pune, will be part of the next report of the Intergovernmental Panel on Climate Change (IPCC), expected to be ready in 2022.
From 1986-2015, the hottest day and coldest night have warmed 0.63°C and 0.4°C, respectively. By the end of the 21st century, the report says, these temperatures are projected to rise by approximately 4.7°C and 5.5°C, respectively, relative to the corresponding temperatures in 1976-2005. This under a hypothetical scenario where no steps are taken to curb global greenhouse gas emissions or the RCP8.5 as it is called.
Currently countries have signed an agreement to reduce emissions to restrict global temperature rise by the end of the century to less than 2°C.
The frequencies of future warm days and warm nights are projected to increase by 55% and 70%, respectively, relative to the reference period of 1976-2005. Summer heat waves over India are projected to be three to four times higher by the end of the 21st century.
The projected rapid changes in India’s climate will place increasing stress on the country’s natural ecosystems, agricultural output, and fresh water resources, the report says.
The reports also notes that aerosol loading, or the levels of fine particulate matter that result from fossil fuel burning, fertiliser use as well as natural processes has substantially increased during the recent few decades.
“This trend in AOD is subject to seasonal variability. The rate of increase in AOD is significantly high during the dry months of December-March,” the report notes. Aerosols play a complicated role. They absorb sunlight and reduce to some extent the heating of the land and ocean surface due to global warming. While a switch away from fossil fuels might reduce aerosol load, increase the greenhouse gas effect of increasing ground temperature, atmospheric water vapour and rainfall, aerosol concentrations also promote clouding and increased intense rainfall over smaller areas such as cities and urban agglomerations.
Roxy Mathew Koll, Scientist at the IITM and associated with IPCC scientific report, said in a statement that an observed change of 0.7°C in average temperatures over India, had already registered a spike in extreme weather events over the region.
“Rainfall patterns have changed, with longer dry spells intermittent with heavy rainfall events. The frequency of very severe cyclones has increased over the Arabian Sea. Over the Himalayas, the glacier retreat is going at a fast pace. Glacier melt and ocean warming are raising the sea level across the Indian Ocean. Recent records show a sea level change of 3cm per decade along the Mumbai coast while it is above 5cm per decade along the Kolkata coast. Now, with the temperatures projected to rise by 2.7°C by 2040 and 4.4°C by the end of the century, we should be ready to face a further increase in the intensity, frequency and extent of these extreme weather events,” Dr Koll said.