Why does the Amazon matter so much?

The Amazon basin covers roughly 6.7 million square kilometers across nine countries, with the majority in Brazil, and contains the largest tropical rainforest on Earth. It holds an estimated ten percent of all known species, including thousands of tree species and enormous undescribed insect diversity, and it stores a very large quantity of carbon in its vegetation and soils. It is also home to hundreds of Indigenous groups, including some living in voluntary isolation, whose territories have measurably lower deforestation rates than surrounding areas.

The lungs of the planet framing is misleading and worth correcting. Mature forests consume nearly as much oxygen through respiration and decomposition as they produce through photosynthesis, so their net contribution to atmospheric oxygen is close to zero. Atmospheric oxygen is abundant and stable on human timescales, and most oxygen production comes from marine phytoplankton. The real stake is carbon: burning and clearing the forest releases stored carbon rapidly, and parts of the southeastern Amazon have been measured as net carbon sources rather than sinks in recent years.

The mechanism that makes it fragile is its own hydrology. The forest recycles water through transpiration, generating atmospheric rivers that produce much of its own rainfall and supply rain to agricultural regions far to the south. Researchers have warned of a tipping point at which sufficient deforestation combined with warming would break that cycle and convert large areas to degraded savanna, a transition that would be effectively irreversible on human timescales. Estimates of where that threshold sits vary and are contested, which is a reason for caution rather than comfort, since the uncertainty runs in both directions.