Deforestation-induced warming caused an extra 28,000 deaths per year in the tropics between 2001 and 2020, according to a new study. The worst-affected region was Southeast Asia, where 8-11 out of every 100,000 people living in deforested areas died due to deforestation-induced warming during this time. Southeast Asia was followed by the tropical regions of Africa and South America.The study, ‘Tropical deforestation is associated with considerable heat-related mortality’, was published in the journal Nature Climate Change on Wednesday (August 27). It was carried out by researchers based at the University of Leeds (the United Kingdom), the National School of Public Health (Brazil), and Kwame Nkrumah University of Science and Technology (Ghana).Tropical forests are some of the most biodiversity-rich environments on the planet. Mainly distributed across South America, Africa and Asia, they are known to soak up large amounts of greenhouse gases — the key reason behind global warming — through photosynthesis. However, in recent decades, these forests have faced large-scale deforestation and deforestation.How has deforestation increased warming?A total of 1.6 million square kilometres of tropical forest area was lost globally between 2001 and 2020, according to the study. Tropical Central and South America (7,60,000 square kilometres) witnessed the maximum forest loss, followed by Southeast Asia (4,90,000 square kilometres) and tropical Africa (3,40,000 square kilometres).Deforestation of tropical forests is primarily driven by agricultural expansion and logging. This has severe implications for local biodiversity, global climate, the hydrological cycle, and human communities.The biggest fallout is that deforestation releases stored carbon into the atmosphere, mainly as carbon dioxide — a greenhouse gas. The scale of this release of carbon is huge, as scientists believe that tropical forests store hundreds of billions of tonnes of carbon in soils and woody trunks. As a result, the global temperatures rise.Also, the loss of tree cover due to deforestation impacts local temperatures. That is because trees and plants take water from the soil and release water vapour, which cools the air above. Once they disappear, this cooling effect also goes away.Story continues below this adThat’s why the study found that “areas of forest loss coincide with areas of strong positive change in temperature across many regions of the tropics”. While temperatures across deforested areas in the tropics saw an increase of an average of 0.7 degrees Celsius between 2001 and 2020, areas that “maintained forest cover” witnessed a warming of just 0.2 degrees Celsius during the same period.For their study, researchers used data of land surface temperatures from the NASA MODIS satellite to map warming in tropical regions between 2001 and 2020. To check the temperature difference, they compared deforestation and surface warming maps of tropical regions.Also in Explained | How extreme heat is affecting IndiaHow has warming caused deaths in deforested areas?Extreme heat can lead to heat stroke and exhaustion. However, it becomes lethal when there is high humidity as well.Joy Merwin Monteiro, assistant professor at Indian Institute of Science Education and Research (IISER), Pune, in a column for The Indian Express, explained: “Humans lose heat generated within their bodies by producing sweat that evaporates on the skin. The cooling effect of this evaporation is essential in maintaining a stable body temperature.”Story continues below this ad“As humidity rises, sweat does not evaporate — just like clothes take a long time to dry in humid locations — and makes it difficult to regulate body temperature. And this could cause a heat stroke, which takes place only when the body temperature goes above 40 degrees Celsius.”In such a case, the body’s metabolism can go haywire, creating a toxin overload which affects multiple organs. This can ultimately lead to death.The heat-related deaths witnessed in the deforested Tropical regions could have happened under similar scenarios. Note that the study did not analyse the change in humidity in deforested areas. However, a 2021 study published in the journal Nature Communications reported that humid heat exposure increases substantially in areas of tropical forest loss compared with nearby forested areas.The latest study found that, on average, six out of every 100,000 people living in deforested areas died as a result of deforestation-induced warming between 2001 and 2020. Overall, it revealed that tropical deforestation drove an additional 28,300 deaths every year during this period. More than half were in Southeast 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.