Human-induced climate change has caused 60% of India to become hotter in April and May over the last six decades

mumbai

Updated: Feb 15, 2020 00:32 IST

Two weeks before the onset of the summer season, new analysis led by the Indian Institute of Technology – Gandhinagar (IIT-Gn)-- reveals that more than 60% of India’s landmass over the last six decades has become hotter in April and May owing to human-induced climate change.

The study, which looked at Indian Meteorological Department (IMD) data of daily maximum temperatures between 1951 and 2015, found that a greater part of the country’s land mass has experienced an increase of more than one degree Celsius in average maximum temperatures during this period.

The study co-authored by Royal Netherlands Meteorological Institute and National Institute of Water and Atmospheric Research, New Zealand, was published in Environmental Research Letters, an international peer reviewed journal by the Institute of Physics, on Thursday.

Of the five major climatic zones for India classified by the six-member team, average maximum summer temperatures have significantly increased in three zones – arid, tropical monsoon and tropical savannah regions by more than 0.1 degree Celsius per decade which is consistent with the rise in global mean annual temperature. The remaining two cold and temperate dry summer zones do not show a statistically significant rise in mean maximum summer temperature during 1951-2015.

Researchers say their findings are significant as the increase in maximum temperatures, especially during summer, has an impact on public health, mortality, water availability, and productivity of labourers. “Concentration of carbon dioxide continues to rise in the atmosphere due to anthropogenic activities, which is directly associated with climate change. Under the rising global mean temperature, the frequency of heatwaves and hottest summers that occurred in the observed record is projected to increase considerably in the future,” said Vimal Mishra, co-author and associate professor, civil engineering department, IIT-Gn. “The alarming rise of temperature extremes can pose serious implications on agriculture, water resources, public health, energy demands, and several other aspects related to society and human well-being.”

According to IMD, 11 of the 15 warmest years since 1901 occurred between 2004 and 2018 with 2016 being the hottest. A 2019 report by the Ministry of Earth Sciences stated that the annual average maximum temperature shows a significant increasing trend of 0.1 degrees Celsius per decade from 1901 to 2018 that is higher than the minimum temperature trend of 0.02 degrees Celsius per decade.

“Heat waves are definitely increasing in India due to global warming especially in north western parts of India, and also towards the south east. If it increases along the coasts, there will be an impact on humidity levels,” said AK Sahai, senior scientist, Indian Institute of Tropical Meteorology, Pune, who was not involved with the study.

In the present study, researchers found that 2010 was the hottest summer during 1951-2015 in three zones: arid and semi-arid regions in north-western parts of India and rain shadow regions in the Indian peninsula, cold Himalayan states, and the Gangetic and Brahmaputra plains and the narrow belt in Punjab-Haryana plains during the same study period.

On the other hand, the tropical monsoon forest regions comprising the west coast and southern parts of the north-eastern states where the southwest monsoon hits the earliest in India and tropical savannah regions that include tropical regions recorded their hottest summers in 1979 and 1973 respectively.

Based on the simulations from the Climate of 20th Century Plus (C20C+) Detection and Attribution project, researchers have concluded that while the hottest summer in 2010 can be attributed to anthropogenic warming, that in 1979 and 1973 cannot.

Based on the hottest years recorded during 1951 and 2015 and climatological average of maximum temperature from 1961 to 1990, maximum temperature during the hottest summer (for each region) was more than 2.3 degrees Celsius in the arid and cold regions of India, above 1.4 degrees Celsius in the temperate and Savannah regions, and more than 1.1 degree Celsius in the monsoon region.

The United Nations Framework Convention on Climate Change in 2015 has pledged to limit global mean surface temperature rise to 1.5 degrees Celsius from the pre-industrial level (1850-1900) by the end of the 21st century. With global mean surface temperatures breaching the one degree limit in 2018 and likely to reach 1.5 degrees Celsius by 2040, the team further carried out simulations to estimate the projected temperature rise over India. Results showed a more than seven-fold and 20-fold increase in the chances of the hottest summers in the observed record under a 2 and 3 degrees Celsius warming world respectively.

“Due to dense population and intensive agriculture, India remains a hot-spot to face the adverse impacts of climate change, which will impact economy and growth. The global community should seriously make efforts to mitigate climate change. In addition, we need to find new ways for climate change adaptation in different sectors to minimise the risk and damage,” said Mishra.