Scientists Show Reforestation Helps Cool the Planet Even More Than Thought

Summary

Replanting forests can help cool the planet even more than some scientists once believed, especially in the tropics. But even if every tree lost since the mid-19th century is replanted, the total effect won’t cancel out human-generated warming. Cutting emissions remains essential. Aftermath of deforestation in the Amazon. (luoman/Getty) In a new modeling study published in Communications Earth & Environment, researchers at the University of California, Riverside, showed that restoring forests to their preindustrial extent could lower global average temperatures by 0.34 degrees Celsius. That is roughly one-quarter of the warming the Earth has already experienced. The study is based on an increase in tree area of about 12 million square kilometers, which is 135% of the area of the United States, and similar to estimates of the global tree restoration potential of 1 trillion trees. It is believed the planet has lost nearly half of its trees (about 3 trillion) since the onset of industrialized society. “Reforestation is not a silver bullet,” said Bob Allen, a climate scientist at UC Riverside and the paper’s lead author. “It’s a powerful strategy, but it has to be paired with serious emissions reductions.” While previous studies have largely focused on trees’ ability to remove carbon from the atmosphere, this research includes another critical dimension. Trees also have an effect on the chemical makeup of the atmosphere in ways that amplify their cooling effect. Trees naturally release compounds known as biogenic volatile organic compounds, or BVOCs. These interact with other gases to form particles that reflect sunlight and encourage cloud formation, both of which help cool the atmosphere. Most climate models do not account for these chemical interactions. “When you include these chemical effects, the net cooling impact becomes more significant,” Allen said. “It’s a crucial part of the picture.” The benefits of reforestation, however, are not evenly distributed. The st...