A four-day storm that struck the Indonesian island of Sumatra in November 2025 has killed an estimated 58 Tapanuli orangutans — roughly 7% of the entire surviving population of the world's rarest great ape — according to a study published in the journal Current Biology. The findings have alarmed conservationists, who warn the species may be the first to be pushed to extinction primarily by climate change.

The Tapanuli orangutan (Pongo tapanuliensis), only formally recognised as a distinct species in 2017, lives in a single fragmented habitat of roughly 1,000 square kilometres in North Sumatra's Batang Toru ecosystem. Fewer than 800 individuals remain. When Cyclone Senyar struck in November 2025, it deposited more than 1,000mm of rain over four days — a record for the area — saturating steep forested slopes and triggering massive landslides. Satellite imagery shows 8,300 hectares of forest, about 11.7% of the orangutans' primary habitat in the so-called West Block, were destroyed. Researchers from Borneo Futures, World Weather Attribution and Liverpool John Moores University overlaid landslide maps with orangutan density estimates to conclude that between 18 and 120 animals — most likely around 58 — were killed, representing 11% of the local population. Only a single carcass was recovered from the debris.

The climate connection is direct and quantified. Scientists with the World Weather Attribution project calculated that human-caused climate change, driven by the burning of fossil fuels and the resulting warming of ocean temperatures, made Cyclone Senyar between 9% and 50% more intense or likely. Under current conditions, such an event is expected roughly once every 70 years — but that interval will shorten as warming continues. "While natural variability comes and goes, these storms will keep getting worse as long as we keep burning fossil fuels," said physicist Friederike Otto, a co-author of the study. Previous research had already established that an annual population loss of just 1% would be enough to drive the Tapanuli orangutan to eventual extinction.

The Batang Toru ecosystem was already under pressure before the cyclone struck. A large hydropower dam, gold mining operations and smallholder agricultural clearing have all reduced and fragmented the orangutans' forest. Researchers are now calling for an immediate moratorium on land-use activities that degrade the remaining habitat, the formal expansion of protected areas, and urgent international biodiversity-recovery financing. The Indonesian government has temporarily suspended major industrial activity in the area to allow scientists to assess the situation. "To prevent the first modern extinction of a great ape species, Indonesia must permanently protect the Batang Toru ecosystem," said conservation biologist Prof Jatna Supriatna of Universitas Indonesia. Researcher Erik Meijaard of Borneo Futures put it starkly: if a storm of this magnitude strikes two or three times within a century, the species will not recover.