Deforestation has killed more than half a million people in the tropics over the past two decades as a result of heat-related illness, a study has found.

Land clearance is raising the temperature in the rainforests of the Amazon, Congo and south-east Asia because it reduces shade, diminishes rainfall and increases the risk of fire, the authors of the paper found.

Deforestation is responsible for more than a third of the warming experienced by people living in the affected regions, which is on top of the effect of global climate disruption.

About 345 million people across the tropics suffered from this localised, deforestation-caused warming between 2001 and 2020. For 2.6 million of them, the additional heating added 3C to their heat exposure.

In many cases, this was deadly. The researchers estimated that warming due to deforestation accounted for 28,330 annual deaths over that 20-year period. More than half were in south-east Asia, owing to the larger populations in areas with heat vulnerability. About a third were in tropical Africa, and the remainder in Central and South America.

The study was published on Wednesday in the journal Nature Climate Change. Researchers in Brazil, Ghana and the UK compared non-accident mortality rates and temperatures in areas affected by tropical land clearance.

Previous studies have shown how cutting and burning trees causes long-term localised warming, but the new paper is the first to calculate the ensuing death toll.

Prof Dominick Spracklen of the University of Leeds said the message was that “deforestation kills”. He expected many people would be shocked by the findings because the local dangers of deforestation were often lost in the global climate debate and the market-focused expansion of agricultural frontiers.

As an example, he pointed to the Brazilian region of Mato Grosso, where there has been massive deforestation to open up land for vast soya bean plantations. Farmers from this area are now pushing for an end to the soy moratorium in the Amazon so they can clear more territory.

Spracklen said leaving the canopy intact would save lives and boost farm production. “If Mato Grosso can keep its forests standing, people there will experience less heat stress,” he said. “This isn’t just the west urging forest protection for the sake of the global climate. The forests directly benefit local communities. They regulate temperature, bring rainfall, and support the agriculture people depend on. These forests aren’t idle – they’re working really hard and doing something really important for us.”