Around 619 million persons in India bore the brunt of climate change-induced extreme heat between June 16 and June 24, according to a study published on Thursday by the United States-based non-profit Climate Central.

This is more than any other country.

China came in second with 579 million individuals exposed to climate change-related heat conditions during the same nine-day period, followed by 231 million in Indonesia, 206 million in Nigeria and 176 million in Brazil.

“In India, one of the country’s worst-ever and long-running heatwaves, which finally relented in mid-June, left more than 40,000 people with heatstroke, with over 100 dead,” the study said. “Temperatures approached 50 degrees Celsius, with a night-time low of 37 degrees Celsius, reportedly the highest ever recorded in India.”

The study, Analysis: Global extreme heat in June 2024 strongly linked to climate change, estimated that “nearly five billion people suffered from climate change-driven extreme heat over nine days in June”.

That is more than 60% of the global population.

The study said that these extreme heat conditions were made thrice as likely to occur due to climate change.

To draw this conclusion, the authors used a tool known as the Climate Shift Index, which “indicates how climate change has altered the frequency of daily high and low temperatures in any location around the world”.

The index ranges between values of -5 to +5. These values are assigned to geographic locations, with positive values indicating that the temperature shift in the region is more likely due to climate change and negative values indicating that it is less likely due to climate change.

A Climate Shift Index-value of zero means that a given location’s temperature, on a given day, “is equally likely in both the modern climate and one without global warming”.

The index is calculated using a combination of two methods.

The first utilises several climate models – or computer simulations – that mimic global temperatures over a period of time, with and without greenhouse gas emissions data.

The second method uses real-world observations of daily high and low temperatures globally, over the last 30 years, to calculate the frequency of a particular temperature in a particular location.

The Climate Shift Index is derived by averaging the estimates produced by both these methods.

In conclusion, the study notes that “every heatwave in the world is now made stronger and more likely to happen by climate change, caused by burning oil, gas and coal, and deforestation”.

“The heatwaves popping up around the world this summer are unnatural disasters that will become more and more common until carbon pollution stops,” said Andrew Pershing, the vice president of Science, Climate Central, in a statement.

The study also flagged the impact of climate change on the Hajj pilgrimage in Saudi Arabia this year, during which at least 645 people, including 68 Indians, died due to extreme heat.

“Climate Central’s analysis found that the city of Mecca has been experiencing temperatures made at least three times more likely due to climate change every day since May 18, and five times more likely since May 24,” the study notes.

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