You may have heard the Amazon described as the lungs of the planet. It is a compelling image and it is also, technically, not quite accurate — the Amazon absorbs roughly as much oxygen as it produces through the combined respiration of all its organisms, leaving the net contribution to atmospheric oxygen close to zero. But the metaphor points at something real even if the mechanism is wrong. The Amazon does something for the planet that nothing else does, and losing it would have consequences far beyond the trees themselves.
The more accurate image is not a lung but a pump. The Amazon basin receives enormous amounts of rain — some parts see more than three metres of it a year. Much of that rain falls on the forest, is absorbed by the trees and soil, and is then released back into the atmosphere through transpiration: a process by which trees pump water up from their roots and release it as vapour through their leaves. A large tree can release hundreds of litres of water vapour in a single day.
Flying Rivers
All of that water vapour has to go somewhere. Atmospheric scientists have a name for what happens next: flying rivers. The Amazon basin generates vast aerial streams of water vapour that flow westward and south, delivering rainfall to regions far outside the forest itself. Brazil's agricultural heartland, one of the most productive farming regions on Earth, receives much of its rainfall not from ocean evaporation but from moisture recycled through the Amazon. Parts of Bolivia, Paraguay, and Argentina depend on the same system.
When large areas of the Amazon are cleared, this cycle is interrupted. Deforested land releases less water vapour, which means less rainfall further downwind. Studies comparing rainfall data before and after large-scale deforestation have found measurable reductions in precipitation in areas that were previously cloud-seeded by the forest, a pattern also tracked by NASA's Earth Observatory using satellite data. The people who depend on that rainfall for crops, rivers, and drinking water are not anywhere near the Amazon. Many of them have never heard of a flying river. But they are affected by what happens inside the basin nonetheless.
The Scale of What Exists
The Amazon basin covers roughly 7 million square kilometres across nine countries, with the large majority in Brazil. The forest is not uniform — it contains dozens of distinct ecosystems, from flooded várzea forests along river margins to dense terra firme forest on higher ground. It is home to an estimated 10 percent of all species on Earth. Around 3,000 species of freshwater fish have been identified in its rivers. New species of mammals, birds, and plants are still being described by scientists every year.
Many of the plants in the Amazon have never been studied for their chemical properties. A significant proportion of pharmaceutical drugs in current use are derived from tropical plants, and the Amazon remains largely unexplored in this respect. What might be there — in terms of compounds that could treat diseases not yet adequately treated — cannot be known until it is studied, which cannot happen after it is gone.
A System Under Pressure
The Amazon has lost roughly 17 percent of its original extent to deforestation, with the pace accelerating in recent decades. The causes are primarily agricultural expansion — cattle ranching and soy farming account for the majority of cleared land — as well as logging, infrastructure development, and, increasingly, illegal gold mining, which causes particularly severe damage by contaminating rivers with mercury.
Scientists tracking the Amazon's health have identified what they call a tipping point: a threshold, estimated at around 20 to 25 percent deforestation, beyond which the forest may no longer be able to generate enough rainfall to sustain itself. Sections of the Amazon have already begun showing characteristics of dryland savanna in what was previously dense forest. Some models suggest parts of the eastern Amazon have already crossed the local tipping point and are in an irreversible transition.
What Remains, and Why It Still Matters
The Amazon that exists today is still the largest tropical rainforest on Earth by a considerable margin. The vast majority of its species are still there. The flying rivers still flow. The question of the Amazon is not one of whether it can be saved — most of it can — but of whether the political and economic conditions for doing so can be created before the remaining intact areas reach the point from which there is no return.
For most people reading this, the Amazon is somewhere they will never go. But the rain that falls on farmland that feeds them, the atmospheric chemistry that shapes the weather where they live, and the biological inheritance of the planet they share — all of these are connected to a forest they may never see. That connection is not abstract. It runs through the water cycle, the carbon cycle, and the web of living things that keeps both functioning. The Amazon's fate is not a regional issue. It is everyone's problem.