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The Amazon is the world's largest rainforest. It harbors immense biodiversity and plays a crucial role in the global climate system by storing vast amounts of carbon in its vegetation.

The Amazon is widely recognized as a major (IPCC: Intergovernmental Panel on Climate Change). Continued deforestation and climate change could push the system past a critical threshold, causing the Amazon to shift from rainforest rich in biodiversity to a degraded savanna-like ecosystem.

A new study, in Communications Earth & Environment, explores long-term future projections of the Amazon ecosystem using state-of-the-art Earth system models.

Researchers assessed long-term changes in the Amazon rainforest from the present through the year 2300 using the state-of-the-art Earth system models from the Coupled Model Intercomparison Project (CMIP5 and CMIP6), which informed the IPCC's Fifth and Sixth Assessment Reports (IPCC: Intergovernmental Panel on Climate Change).

They defined "dieback" as severe loss of photosynthetic activity by the end of the 23rd century compared to the 19th century in areas that were originally highly productive under high-emission scenarios. The scientists then analyzed the climatic and ecological conditions under which such drastic shifts could occur.

The majority of considered models project Amazon dieback, although the timing and spatial extent vary across models. The results of Earth system model simulations suggest that the dieback could begin as early as the 21st century under a wide range of global warming levels, starting from 1.5°C and triggered by extreme conditions—large increases in the annual surface air temperatures, decreases in precipitation and intensified by land-use change from forest to agricultural lands.

However, current Earth system models may underestimate future risks, as many do not fully represent key ecological processes in tropical forests, such as fire dynamics and drought-induced tree mortality.

The new study also uncovers the key mechanisms behind Amazon dieback. Over the long term, global warming weakens the Atlantic Meridional Overturning Circulation (AMOC), a major system of ocean currents, which in turn shifts the Intertropical Convergence Zone (a vital tropical rain belt) southward.

This shift results in hotter and drier conditions across the northern Amazon. Furthermore, rising carbon dioxide levels reduce evapotranspiration, the process by which trees release moisture into the air, thereby weakening the Amazon's natural water recycling system and contributing to regional drying.

In addition, long-term projections under high-emission scenarios show more frequent El Niño–like warming patterns, which intensify heat and drought across the basin. While previous studies have examined warming patterns, circulation shifts and ecosystem impacts, this study is the first to demonstrate Amazon dieback across multiple Earth system model projections and to explain its underlying drivers.

These climatic changes set off a cascade of ecological disruptions. Hotter and drier conditions reduce the efficiency of photosynthesis and increase plant respiration, tipping the rainforest's carbon balance. Declining rainfall and soil moisture limit water availability and hinder nutrient transport, stressing tree health and regeneration.

As a result, tropical forest ecosystems become less productive, more vulnerable to disturbance, and eventually cross a threshold beyond which they can no longer sustain dense vegetation. Combined with widespread land-use change, especially in the southern Amazon, these shifts push the region toward large-scale ecosystem collapse.

The study's findings highlight the urgent need to limit greenhouse gas emissions and protect the Amazon's resilience. Continued warming, land-use change, and ecosystem degradation could soon push the rainforest past a tipping point, with global climate consequences.

The lead author, Dr. Irina Melnikova, also cautions that future research should focus on improving the representation of ecological processes in models to better anticipate the risks. Protecting the Amazon requires coordinated international action, integrating climate mitigation, sustainable land management, and conservation strategies.