Nearly 740,000 excess deaths in India annually can be attributed to abnormal hot and cold temperatures related to climate change, according to a study published in The Lancet Planetary Health journal.

An international team, led by researchers at Monash University in Australia, found that globally more than five million extra deaths a year can be attributed to non-optimal temperatures.

The study published on Wednesday found that deaths related to hot temperatures increased in all regions from 2000 to 2019, indicating that global warming due to climate change will make this mortality figure worse in the future.

In India, the number of deaths per year linked with abnormal cold temperatures is 6,55,400, while the number of deaths associated with high temperatures is 83,700, according to the researchers.

The team looked at mortality and temperature data across the world from 2000 to 2019, a period when global temperatures rose by 0.26 degrees Celsius per decade.

The study, the first to definitively link non-optimal temperatures to annual increases in mortality, found 9.43 per cent of global deaths could be attributed to cold and hot temperatures.

This equates to 74 excess deaths for every 1,00,000 people, with most deaths caused by cold exposure.

Global warming may “slightly reduce the number of temperature-related deaths, largely because of the lessening in cold-related mortality,” said Professor Yuming Guo, from the Monash University.

“However in the long-term climate change is expected to increase the mortality burden because heat-related mortality would be continuing to increase,” Guo said.

The data show geographic differences in the impact of non-optimal temperatures on mortality, with Eastern Europe and Sub-Saharan Africa having the highest heat and cold-related excess death rates.

Cold-related death decreased 0.51 per cent from 2000 to 2019, while heat-related death rose 0.21 per cent, leading to a reduction in net mortality due to cold and hot temperatures.

Of the global deaths attributed to abnormal cold and heat, the study found more than half occurred in Asia, particularly in East and South Asia.

Europe had the highest excess death rates per 100,000 owing to heat exposure, according to the researchers. Sub-Saharan Africa had the highest death rates per 100,000 because of exposure to cold, they said. The largest decline of net mortality occurred in Southeast Asia while there was temporal increase in South Asia and Europe.

Previous studies had looked at temperature-related mortality within a single country or region. “This is the first study to get a global overview of mortality due to non-optimal temperature conditions between 2000 and 2019, the hottest period since the Pre-Industrial era,” Guo said.

The researchers used data from 43 countries across five continents with different climates, socio-economic and demographic conditions and differing levels of infrastructure and public health services.

“The study had a large and varied sample size, unlike previous studies,” Guo added.

The mortality data from this study are significantly higher than the second-largest study published in 2015, conducted across 13 countries/regions, which estimated 7.7 per cent of deaths were related to cold and hot temperatures.

“The importance of taking data from all points of the globe was to get a more accurate understanding of the real impact of non-optimal temperatures under climate change,” Guo said.

Understanding the geographic patterns of temperature-related mortality is important for the international collaboration in developing policies and strategies in climate change mitigation and adaptation and health protection, he added.