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Cutting down rainforests for palm oil in Indonesia and Malaysia could encourage longer El Ni帽o and La Ni帽a events with far-flung climate impacts, according to modelling research.

An El Ni帽o event, like the one that began earlier this year, occurs when easterly trade winds weaken, allowing warm water to slosh from the western Pacific back into the eastern Pacific and heat the atmosphere. In La Ni帽a, the alternate phase of the El Ni帽o-Southern Oscillation (ENSO), stronger trade winds cool the Pacific.

Research suggests that stronger and longer-lasting El Ni帽o and La Ni帽a events are more frequent, and a in May found that human-caused global warming was partly to blame. But a new study by at the University of California, Irvine, and his colleagues is the first to suggest that deforestation could also contribute.

The islands of South-East Asia, which climatologists collectively refer to as the Maritime Continent, are home to the world鈥檚 third largest rainforest. If all of these trees were cut down, the islands would become drier and hotter, and more warm air would rise into the atmosphere there, the researchers鈥� model showed. This enhanced atmospheric circulation would intensify trade winds blowing south-west from Mexico, starting a feedback loop: stronger winds would cool the water and increase evaporation, which would strengthen winds further.

As a result, the frequency of multi-year as opposed to single-year La Ni帽a events increased from 79 per cent of the time with the real-world vegetation to 88 per cent in the hypothetical total deforestation scenario. Multi-year El Ni帽o events also rose, but only from 40 to 45 per cent of the time. Longer La Ni帽as and El Ni帽os can have disastrous effects, like the deadly drought that hit Somalia during the 2020 to 2023 La Ni帽a.

鈥淏eside burning [fossil fuels and] releasing carbon dioxide, cutting trees is another way to profoundly, significantly change how our climate machine operates,鈥� says Yu.

In the simulation, total deforestation also set the stage for El Ni帽o to happen more often in the central Pacific and less often in the eastern Pacific. That would mean different impacts, like colder winters in Florida rather than in California, says Yu.

Although deforestation rates have fallen in Indonesia and Malaysia, hundreds of thousands of hectares were still last year to produce palm oil for processed food, shampoo and other products.

at the US National Oceanic and Atmospheric Administration says while these findings raise further concerns about rainforest loss and should be tested with other climate models, the effect of deforestation on El Ni帽o and La Ni帽a is minimal for now.

鈥淭here will be bigger changes in the ENSO cycle because of the increasing concentrations of greenhouse gases in the atmosphere than are going to result from this hypothetical turning of Indonesia into a treeless savannah,鈥� he says.