If deforestation and global warming continue unchecked, the Amazon rainforest could begin a gradual transition to a degraded, grassland-like ecosystem in just a few decades, according to new research published on Wednesday.<\/p>\n
The study, published in the journal Nature<\/a>, provides new insight into when the forest might start to slip over a so-called tipping point<\/a> at which an incremental but profound and irreversible ecosystem transformation begins.<\/p>\n The analysis examined the relationship between deforestation and global warming. Deforestation can worsen the effects of rising temperatures by reducing rainfall. Those intensified effects, in turn, can lower the warming threshold at which ecosystem changes begin.<\/p>\n \u201cThe consequences of the Amazon tipping point are catastrophic for the entire planet,\u201d said Bernardo M. Flores, an ecology researcher at the University of Santiago de Compostela in Spain and an author of the study. \u201cWe need to be careful not to get anywhere near those risks.\u201d<\/p>\n The Amazon, home to millions of species of plants and animals, is the largest tropical rainforest on Earth. Year after year, it absorbs more than a billion tons of planet-warming carbon dioxide from the atmosphere, helping to offset the effects of human-caused emissions.<\/p>\n In past decades, though, wildfire, logging, mining and expanding agriculture have taken a heavy toll on the rainforest. Degradation has caused some areas, like an infamous \u201carc of deforestation\u201d that stretches across Brazil, to become a source of planet-warming carbon<\/a> rather than a so-called sink where carbon is locked away.<\/p>\n Recently, tropical countries, and notably Brazil, have made progress<\/a> in slowing deforestation. And research shows that some tropical forests are capable of regrowing quickly<\/a>, although some areas of the Amazon are already too degraded to recover without human help.<\/p>\n The new study examines a known consequence of deforestation: it can create a feedback loop that reduces rainfall and causes even more trees to die. That\u2019s because trees in the rainforest act as a kind of weather machine by sucking up water from the ground with their roots and releasing moisture into the air through their leaves.<\/p>\n When trees are lost on a large scale, the regional climate becomes drier and other effects of climate change, like drought and wildfire, become more dangerous.<\/p>\n \u201cIf you lose forests, then you lose rainfall,\u201d Dr. Flores said. \u201cThis interaction between rain and forests is at the heart of the Amazon\u2019s resilience.\u201d<\/p>\n Separate research has found that deforestation has played a role in the majority of rainfall declines<\/a> in the Amazon in recent decades, with the most heavily deforested regions sustaining correspondingly larger reductions in rainfall.<\/p>\n Usually, scientists study the effects of deforestation and climate change separately, said Nico Wunderling, a professor of computational Earth system sciences at the University of Frankfurt, who led the research published on Wednesday. The new study is one of the first that looks comprehensively at both factors to determine a tipping point, he said.<\/p>\n In a theoretical world without deforestation in the Amazon, the rainforest would be able to withstand up to 3.7 degrees Celsius, or about 6.7 degrees Fahrenheit, of global warming over preindustrial temperatures, the researchers found.<\/p>\n But in today\u2019s world, the planet has already warmed an estimated 1.4 degrees Celsius<\/a> and at least 17 percent of the Amazon rainforest has already been cut down, burned or otherwise lost.<\/p>\n That means a tipping point could be reached relatively quickly, the researchers found. According to their analysis, in a scenario where 22 percent or more of the Amazon rainforest is deforested, the majority of the ecosystem becomes vulnerable to collapse at temperatures over 1.5 degrees Celsius of warming.<\/p>\n If both global warming and deforestation continue at the current pace, this danger zone could be reached in about 25 years, according to Dr. Flores.<\/p>\n It is also possible, Dr. Wunderling said, that the Amazon could avoid a midcentury tipping point if Brazil continues to successfully slow deforestation.<\/p>\n More than 140 countries have agreed to halt and then reverse forest loss by 2030<\/a>, but deforestation remains 70 percent higher than the level needed for the world to meet that commitment, a recent report<\/a> found.<\/p>\n