The Amazon rain forest, like other tropical forests, depends on rain to survive: Once rainfall drops to a certain level, the forest can dry out, burn, and start to turn into a savannah. A new study suggests that a huge swath of the Amazon forest—around 40%—is already at the point where that transition is at risk of happening.
The study, published in Nature Communications, modeled what could happen in tropical forests globally over time as the climate changes. As forests get hotter, less rain is falling, and the ecosystems are becoming less resilient. “We understand now that rain forests on all continents are very sensitive to global change and can rapidly lose their ability to adapt,” co-author Ingo Fetzer said in a statement.
Deforestation is making the problem worse. When the conditions are right, the Amazon rain forest can create its own rain. Water vapor from leaves makes low-level clouds, and the rain helps prevent fires and makes the forest grow. But as the forest shrinks from logging and fires, the rainfall cycle drops, and it’s harder for the rest of the forest to recover. Rainfall levels in 40% of the Amazon are now low enough that the area could feasibly convert to grasslands. The rain forest is also experiencing its worst fires in a decade, with nearly 30,000 active fires.
The shift from rain forest to savannah would take time, but it’s hard to stop after it’s in motion. (And the solution isn’t as simple as planting trees.) It would mean a massive loss of biodiversity. The Amazon forest, alone, is home to at least 40,000 species of plants, hundreds of mammal species, hundreds of reptile species, hundreds of amphibian species, more than a thousand species of birds, thousands of fish species, and tens of thousands of species of insects, if not more. It’s also a critical piece of the fight against climate change, absorbing around 2 billion tons of greenhouse gas emissions per year.