How the Amazon Rainforest Regulates Climate Beyond Its Own Borders

A Forest That Creates Its Own Weather—and Much of South America's

The Amazon basin covers approximately 7 million square kilometers—roughly the size of the continental United States. Within it live an estimated 390 billion individual trees representing around 16,000 species, forming a canopy so vast that the forest generates its own precipitation system. Brazilian scientist José Marengo and colleagues have documented how the Amazon exports moisture to agricultural regions thousands of kilometers away, making the rainforest less a passive recipient of climate and more an active generator of it. Disrupting this system has consequences that extend far beyond the forest's borders.

The Carbon Sink: Size and Recent Changes

Living biomass stores carbon. A mature Amazon tree may contain several tons of carbon in its wood, leaves, and roots. The entire Amazon stores an estimated 150–200 billion metric tons of carbon—equivalent to roughly 15–20 years of current global fossil fuel emissions. When trees grow, they pull CO₂ from the atmosphere; the Amazon has historically been a substantial net carbon sink, absorbing more CO₂ than it releases.

That sink function has been diminishing. A landmark 2021 study by Luciana Gatti and colleagues, published in Nature, found that the eastern Amazon—the portion most heavily affected by deforestation and fire—had flipped from carbon sink to carbon source. The eastern Amazon now emits more CO₂ than it absorbs, particularly during the dry season when fires set to clear land for agriculture release stored carbon directly into the atmosphere.

• The Amazon absorbed an estimated 2 billion tons of CO₂ per year in the 1990s
• By the 2010s, net absorption had declined by roughly 30%
• The eastern Amazon's net annual CO₂ emissions now exceed those of some individual countries
• The western Amazon continues to function as a carbon sink, but for how long depends on the deforestation trajectory

Flying Rivers: The Amazon's Moisture Export System

The Amazon doesn't just receive rainfall—it manufactures it. Trees absorb groundwater through roots and release it as water vapor through leaves in a process called evapotranspiration. A single large Amazon tree can transpire 1,000 liters of water per day. The forest as a whole releases approximately 20 billion metric tons of water vapor into the atmosphere daily—more than the Amazon River itself discharges into the Atlantic Ocean.

This water vapor doesn't simply rise and fall as local rain. Prevailing wind patterns carry it westward, where the Andes mountain range acts as a barrier, deflecting moisture southward across Brazil into the Paraná basin, Uruguay, and northern Argentina. These atmospheric rivers of moisture—dubbed rios voadores (flying rivers) by Brazilian researchers—supply rainfall to the agricultural heartland of south-central Brazil, the world's largest soybean exporter and a major producer of corn, coffee, and sugarcane.

Rainfall Recycling Within the Forest

The Amazon recycles moisture internally through multiple cycles before water exits the basin entirely. Rainfall enters the forest, a portion runs off into rivers, but most is intercepted by vegetation and returned to the atmosphere through evapotranspiration. Studies have estimated that water molecules over the Amazon interior are recycled through the atmosphere five to seven times before leaving the basin.

Temperature Regulation

Tropical forests cool their surrounding environment through two mechanisms. Evapotranspiration consumes energy (latent heat) that would otherwise warm the air—the same reason sweating cools the human body. Forest canopies also have relatively high albedo (reflectance) compared to bare ground or pasture, reflecting more solar radiation back into space. Studies comparing cleared areas to intact forest show temperatures 2–4°C higher in deforested patches—and regional climate modeling suggests large-scale deforestation could raise temperatures across the Amazon basin by 3–8°C, reducing rainfall by 20–30%.

The Tipping Point: How Close Is It?

The most alarming concept in Amazon science is the tipping point: a threshold at which deforestation causes enough decline in evapotranspiration that the remaining forest can no longer generate sufficient rainfall to sustain itself. Below this rainfall threshold, the humid tropical forest—which requires approximately 1,500 mm of annual precipitation to maintain—gives way to savanna or degraded scrubland. The forest dies from the inside out.

Carlos Nobre and Thomas Lovejoy, in a widely cited 2018 Science Advances paper, estimated that 20–25% deforestation of the Amazon could trigger this tipping point for the eastern and southern Amazon. Deforestation has already removed approximately 17–20% of the original forest, placing the system alarmingly close to or potentially within the tipping zone by the higher estimates.

• Combined deforestation and climate-change-driven droughts are acting synergistically—the 2010 and 2015–2016 droughts, both among the worst on record, killed billions of trees
• Forest degradation from fire and selective logging affects an area comparable to outright deforestation but is less visible in satellite counts
• Legal deforestation rates in Brazil dropped over 80% between 2004 and 2012 under government policy, then rose sharply after 2018 before declining again following the 2022 election

Global Feedback Loops

The Amazon's climate significance extends beyond South America. Moisture exported via flying rivers connects to weather systems across the Atlantic. The Amazon's albedo affects global radiative balance. If the Amazon transitions to savanna, the released carbon pulse would dwarf annual human emissions for years, potentially pushing global temperatures above 1.5°C thresholds far faster than current projections suggest. The forest's role as a planetary thermostat makes its preservation one of the highest-leverage climate interventions available—and its degradation one of the most consequential risks.