How forests create clouds to help cool the planet

Recent deadly heatwaves across Europe are part of a larger global pattern. In 2023, the Amazon experienced a historic drought that shrank the Rio Negro and Rio Madeira, two crucial waterways that converge to form the Amazon River. In 2024, the dried-up land was consumed by 280,000 fires that destroyed 30 million hectares of forest, a third more than in the previous drought year.  

Scientists say that the record heat of 2023–2024 cannot be explained by the expected effects of El Niño and reduced air pollution alone, prompting investigation of decreasing cloud cover as a factor.  

To understand this connection, we need to examine the role of forests.  

How it works 

Forests, especially in tropical regions like the Amazon, the Congo Basin, and parts of tropical Asia, contribute to cloud formation. Clouds help regulate local and regional temperatures by reflecting incoming solar radiation and provide cover, keeping ecosystems cool, wet, and shaded – essential conditions for the survival of plants, animals, rivers, and people.  

In a process known as evapotranspiration, trees pull water from the soil and release it into the atmosphere. Trees also release natural organic compounds that can react in the atmosphere to form organic aerosols, tiny airborne particles that help water vapour condense into cloud droplets.  

When entire tropical forests do this together, the vapour forms massive flows of clouds, known as ‘flying rivers’. Like the waterways that feed into the Amazon River, these aerial pathways flow together into heavier channels, distributing clouds and rain across continents.    

Trees in the Amazon release an estimated 20 billion tonnes of water into the air every day. The vapourised water is carried along in the air in ‘flying rivers’ until it rains down on the lowlands and the Andes mountain slopes, feeding the Amazon River and replenishing water supplies in the rainforest, completing the cycle. 

Any disruption to this cycle can have far-reaching consequences in the Amazon and globally. Tropical forests stand between us and record temperatures that threaten life on Earth. 

What is changing now 

Deforestation is disrupting the vital cycle of forests, clouds, and climate. Losing trees means losing their cloud-making power, and risks triggering another cycle of drought and fire.  

As forests lose trees, less water is released into the air, contributing to hotter and drier conditions. Cloud cover is lost, leaving ecosystems and people unprotected. Rainfall decreases, leading to drought and fires. Waterways dry up and rainforests go thirsty, causing more deforestation.  

The impacts of this disruption can already be seen.  

Over the past two decades, research points to a global trend of declining cloud cover over tropical forests in mountainous areas. As cloud cover has declined, temperatures have risen, sometimes faster than the global average, while air pressure has increased and soil moisture and rainfall have decreased.  

Further research has found evidence that deforestation has reduced rainfall across the tropics, including in the Amazon, the Congo Basin, and Southeast Asia. By some projections, tropical forests are expected to see a 20% decrease in rainfall by 2100. 

Ecosystems are also feeling these impacts. Research suggests that changes in the Amazon water cycle are affecting frog populations and diversity in the Atlantic Forest, demonstrating how disruptions to flying rivers go beyond the Amazon itself.  

While forests act as natural carbon sinks, degradation and deforestation can release carbon dioxide and other greenhouse gases into the atmosphere, worsening climate change.  

Losing forests also means losing their contribution to climate change mitigation and adaptation, and their role as sustainable producers of raw materials and providers of ecosystem services. 

What we can do about it 

Healthy, resilient forests are crucial defenses against the climate crisis. Responsible forest management can and must play a part. Ensuring that we have more trees standing, especially in vital ecosystems like the Amazon, supports the processes that sustain cycles of cloud formation and natural climate regulation. 

Responsibly managed forests rely on Indigenous and local communities, whose knowledge and stewardship have sustained these ecosystems for generations. Supporting their leadership and management strengthens forest resilience while helping communities adapt to climate impacts they are often the first to face.  

Read more: FSC Climate and Biodiversity Strategic Framework 2026–2032