Study finds 2023–2024 El Niño drought and heat signal 'new normal' for tropical forests

A study published in Earth's Future found that during the 2023–2024 El Niño, about 75% of the world's tropical forest areas experienced at least six months of unprecedented simultaneous drought and heat. According to the study, the scenario offers more than a snapshot of an extreme event: it offers a preview of the "new normal" for the next two decades if greenhouse gas emissions are not reduced. The Amazon is the region most vulnerable to this pattern, the study states.

If global greenhouse gas emissions continue to rise, the likelihood of the Amazon experiencing droughts as severe as those of the past two years will increase ninefold by the end of the century, even in years not influenced by El Niño, according to the study. Under thermal stress of this magnitude, tropical forests undergo functional collapse, the researchers said. Instead of absorbing the gases that warm the planet, these areas temporarily begin to emit carbon into the atmosphere, they said.

The study found that high average temperatures are expected to become at least six times more likely across all tropical regions, even under a scenario of lower global emissions. Under that scenario, by around 2075 the world would emit an amount of carbon equivalent to what it removes from the atmosphere, a condition known as net-zero CO₂ emissions.

Johanna Van Passel, the corresponding author, said: "During the 2023–2024 El Niño, the area and duration of droughts and heat waves were the largest and most extensive in the past 25 years. When we apply the same models to the future, we see that temperatures are rising. We're concerned because, unfortunately, it could be even worse now." Van Passel is a scientist at Ghent University in Belgium and a visiting researcher at the Institute of Biology at the State University of Campinas (IB-UNICAMP) in Brazil.

According to Phys.org, the need for mitigation is even more urgent given the impending 2026–2027 El Niño, whose effects are already being felt in South America. Forecasts indicate it will reach the "very strong" category, the highest classification, by the start of summer. The article reports that the El Niño is on track to be the most intense ever recorded.

To reach these results, the scientists combined satellite and observational data with projections from 24 climate models for four emissions scenarios, covering the past (2000–2024) and the future (through 2100). They also used an anomaly-based approach, which takes into account each region's baseline climate, to define extreme events.