Climate change-fuelled landslides push rarest great ape closer to extinction

Published in Current Biology, scientists analysed the impact of Cyclone Senyar on Indonesia's critically endangered Tapanuli orangutans.

They found that the storm’s extreme rainfall in November 2025 resulted in landslides that delivered a severe demographic shock to a species already on the brink of extinction.

The scientists, including Nottingham Trent University's Professor Dave Petley, analysed satellite evidence of landslide scars in the West Block of the Batang Toru Ecosystem - home to the largest remaining population of the apes.

These were overlaid with estimates of orangutan density in the area. They concluded that an estimated 58 Tapanuli orangutans died as a result of the landslides - about 11% of the total living in this region, or 7% of the estimated overall population remaining in the wild.

Using climate attribution methods, the scientists also found that the rainfall intensity was increased by as much as 50% as a result of human-induced climate change, demonstrating how worsening weather extremes present a growing threat to endangered wildlife.

Key Findings:

● Severe Population Impact: Landslides resulting from downpours during Cyclone
Senyar are estimated to have caused the loss of about 11% of the critically-endangered Tapanuli orangutan population in the West Block region.

● Habitat Destruction: Approximately 8,300 hectares of forest, accounting for about
11.7% of the forest cover in the West Block of the Batang Toru region, were affected by landslides triggered by extreme rainfall.

● Climate-fuelled destruction: Attribution analysis shows that human-induced climate change increased the rainfall intensity by between 9 and 50%.

Professor Erik Meijaard, Chief Scientist at Borneo Futures said: “This level of loss is substantial for a species with such a small total population. When combined with ongoing pressures such as habitat degradation and human–wildlife conflict, it further increases the urgency of implementing and adequately resourcing a coordinated species action plan.”

Professor Jatna Supriatna, Department of Biology, Universitas Indonesia, said: "The loss of an estimated 58 Tapanuli orangutans to a single climate-induced landslide event is a devastating demographic shock to the world’s rarest great ape. To prevent the first modern extinction of a great ape species, Indonesia must permanently protect the Batang Toru ecosystem, but our international partners must also meet their global commitments by providing immediate biodiversity-recovery financing."

Professor Serge Wich, Primatologist at Liverpool John Moores University, said:
“It is tragic to lose so many apes in this way. In landscapes where populations are small and fragmented, this type of weather or climate event can have population-level consequences. It is extremely worrying for the future of this ape.”

Professor Dave Petley, Landslide Researcher at Nottingham Trent University, said: “These are high-velocity, shallow landslides triggered by intense rainfall. Because the debris flows are directly connected to the channel system, the failure is rapid and exceptionally destructive, leaving those in the path with little warning or chance of escape.”

Professor Friederike Otto, Professor of Climate Science at Imperial College London, said: “This study is a stark demonstration of how intertwined the crises of climate change and biodiversity loss are. By increasing the rainfall intensity of Cyclone Senyar by up to 50%, human-induced climate change turned a severe tropical storm into a catastrophic trigger for these tragic landslides.”