Headed for a routine doctor visit last year, Asha Sonawane, 63, collapsed after stepping outside her house in Bhadole village of India’s Maharashtra state as temperatures soared past 40 degrees Celsius (104 F). Her daughter Alka rushed to her with lime water and an energy drink, which relieved her a bit. But her legs hurt and she felt weak. Dehydration in extreme heat had exacerbated Sonawane’s diabetes mellitus – a chronic medical condition in which blood glucose levels are too high – her doctor later explained.
He prescribed a few medicines and told her not to go outside for the rest of the summer.
During her long months indoors, she kept feeling dizzy despite taking the medications. Sonawane, who has had diabetes since 1997, said that even 10 years ago, she walked a lot and even worked eight or more hours a day in the field.
“I never experienced anything like this,” she said.
As heat-trapping gases cause the climate to warm, one often overlooked consequence of extreme heat is its impact on people with diabetes mellitus: 830 million people globally, 101 million of them in India.
The most common forms of diabetes are type 1 and type 2. In type 1, the immune system attacks the pancreas, producing little to no insulin. Type 2 diabetes, which is more prevalent, occurs when the body’s cells become resistant to insulin, and the pancreas cannot produce enough insulin to meet the body’s needs.
World Health Organization data shows diabetes has skyrocketed by 315% since 1990, with cases surging in low- and middle-income countries. A 2017 study indicated that rising heat may explain some of that rise, perhaps by reducing the activity of a certain kind of fat. The researchers found that a one-degree Celsius rise in temperature could cause over 100,000 new diabetes cases annually in the U.S. alone.
In 2021, more than 2 million people worldwide died from diabetes and related kidney diseases, and more than half those affected by diabetes did not take medications in 2022. Still more could suffer as global warming exacerbates the disease. One study found that in a high-emission scenario, China’s heat-related diabetes mortality could multiply eightfold by the 2090s.
In 2024, the Earth’s average temperature for the first time climbed 1.5 degrees Celsius above the preindustrial revolution level, the limit targeted by the 196 countries that signed the Paris Agreement in 2015. With that level breached, scientists warn of graver consequences as the Earth warms.
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The World Meteorological Organization confirmed that 2024 was the hottest year on record, and roughly 6.8 billion people, or 78% of the world’s population, experienced extreme heat for at least 31 days that year.
Many people with diabetes may not