A major international study has warned that the Amazon rainforest is moving towards a new and extreme climatic state described as ‘hypertropical’, as droughts become longer, hotter and more frequent. Scientists say these conditions have no modern parallel and could fundamentally alter the world’s largest rainforest within this century.
What does ‘hypertropical’ mean?
The term hypertropical has been coined by researchers to describe climate conditions that go beyond what is currently defined as tropical. Based on more than three decades of field measurements across the Amazon, the study suggests that rising temperatures combined with prolonged droughts are pushing forests into a state unseen on Earth for millions of years.
Trees under extreme stress
Researchers analysed how trees and soils respond during severe heat and drought events. They found that reduced soil moisture is already causing widespread stress to trees, triggering hydraulic failure—where water transport inside trees breaks down—and carbon starvation, which occurs when trees close leaf pores to conserve water, limiting photosynthesis.
If these conditions become common, tree mortality could increase by up to 55 per cent, the study warns.
Secondary forests at greater risk
The findings show that fast-growing trees with low wood density are the most vulnerable. These species dominate secondary forests, which often regenerate after logging or fires. As a result, secondary forests may suffer higher death rates during future droughts, weakening forest recovery and resilience.
El Niño droughts offer a warning
The study closely examined drought impacts during the 2015 and 2023 El Niño events, which brought unusually high temperatures. Scientists observed that trees across different Amazon regions reached similar critical water stress thresholds, suggesting the risk is widespread rather than localised.
From carbon sink to carbon source
One of the most alarming projections is that large parts of the Amazon could shift from absorbing carbon dioxide to emitting it, as dying trees release stored carbon. While most hypertropical forests are expected to emerge in the Amazon, similar changes could occur in parts of Africa and Asia.
Why this matters globally
The Amazon plays a crucial role in regulating the global climate. A weakened rainforest would accelerate climate change, with impacts felt far beyond South America.
Researchers stress that human action remains decisive. Reducing greenhouse gas emissions could delay or limit the emergence of hypertropical conditions, while continued high emissions would bring this future closer.