This death toll is expected to rise in the coming years as climate change makes wildfires more frequent and intense, according to the study in The Lancet journal. The international team of researchers looked at existing data on “landscape fires”, which include both wildfires that rage through nature and planned fires such as controlled burns on farming land.

Around 450,000 deaths a year from heart disease were linked to fire-related air pollution between 2000 and 2019, the researchers said. A further 220,000 deaths from respiratory disease were attributed to the smoke and particulates spewed into the air by fire. From all causes around the world, a total of 1.53 million annual deaths were associated with air pollution from landscape fires, according to the study.

More than 90 percent of these deaths were in low and middle-income countries, it added, with nearly 40 percent in sub-Saharan Africa alone. The countries with the highest death tolls were China, the Democratic Republic of Congo, India, Indonesia, and Nigeria. A record amount of illegal burning of farm fields in northern India has been partly blamed for noxious smog that has recently been choking the capital New Delhi.

The disparity between rich and poor nations further highlights “climate injustice”, in which those who have contributed the least to global warming suffer from it the most, they added. Some of the ways people can avoid smoke from fires – such as moving away from the area, using air purifiers and masks, or staying indoors – are not available to people in poorer countries, the researchers pointed out.