About three-quarters of the world’s tropical forests were hit by unusually severe heat and drought during the 2023-24 El Niño. That is the central finding of a study published this week in Earth’s Future, led by Johanna Van Passel of Ghent University in Belgium. The team compared 12 datasets of heat and drought observations from 2000 to 2024 and then projected conditions to 2100. Here are the numbers that matter.
75%: forests hit by drought and heat together
The authors found that three quarters of pantropical forests experienced, on average, 6 months of compound droughts and heatwaves during 2023–2024. Compound means hot and dry at once, which is harder on trees than either alone.
15.9 million sq km: the area studied
The data covered the Americas (8.4 million sq km), Africa (3.6 million) and Asia (3.9 million). That is nearly the whole tropical forest belt, so this is not a regional snapshot.
88%, 89% and 43%: how the continents compare
Compound hot-dry events hit on average 88 per cent of American forest area and 89 per cent of African forest area, followed by 43 per cent of Asian forests. Asia got off more lightly, though not lightly.
18 months: how long the heat lasted
According to the AGU press release, all tropical forests stayed unusually hot for roughly 18 months, on average. Rainfall was also short: 80% of forests were drier than usual, and parts of the Amazon had a full two years of anomalous drought. At Manaus in Brazil, water levels at the port sank to their lowest since records began over a century ago.
Six times: the odds, even with carbon neutrality
Even if humanity reaches carbon neutrality by 2075, the high annual temperatures of 2023 and 2024 will become at least six times more likely in all tropical regions by 2100, compared with the past 25 years. Under high emissions, the authors say, such heat could become the “new normal” for tropical forests in less than 20 years.
Nine times: the Amazon’s drought risk
Heat is expected to spread across most forest regions, but drought risk rises mainly in the Amazon. Under high emissions, Amazon droughts of comparable severity could become nine times more likely by 2100.
Taken together, the figures describe a forest belt that spent the better part of two years under stress, with the Americas and Africa taking the worst of it. That matters for carbon. Separate research on the same El Niño found that tropical land acted as a carbon source in both 2023 and 2024. Earlier plot-by-plot work in South America found that tree deaths jumped in the extreme heat. Of the southeastern Amazon, Beatriz Marimon of Brazil’s Mato Grosso State University said the trees “may have now switched from storing carbon to emitting it.”
