Planting a trillion trees could be the "most effective solution" to climate change, study says

If a tree falls in a forest, will replanting it help curb global warming? Scientists say planting a trillion trees globally could be the single most effective way to fight climate change. 

According to a new study in the journal Science, planting billions of trees around the world would be the cheapest and most effective way to tackle the climate crisis. Since trees absorb carbon dioxide, which contributes to global warming, a worldwide planting initiative could remove a substantial portion of heat-trapping emissions from the atmosphere.

The researchers say a program at this scale could remove about two-thirds of the carbon dioxide (CO2) emissions caused by human activities since the start of the industrial revolution, or nearly 25% of the CO2 in the atmosphere.

The scientists used Google Earth mapping to determine there is enough space globally to plant more than a trillion trees without interfering with existing farmland or cities. According to the study, an area of trees about the size of the United States could scrub 205 billion metric tons of carbon from the atmosphere — out of the roughly 300 billion metric tons of man-made carbon pollution produced over the past 25 years. 

"This is by far — by thousands of times — the cheapest climate change solution," study co-author Thomas Crowther, a climate change ecologist at the Swiss Federal Institute of Technology in Zurich, told The Associated Press.

He stressed the need for urgent action, given how rapidly climate change is already progressing, and said tree planting would have near-immediate results, since trees remove more carbon when they are younger. 

"It's certainly a monumental challenge, which is exactly the scale of the problem of climate change," Crowther said.

Russia, the United States, Canada, Australia, Brazil and China have the most available room for reforestation. The study's lead author, Jean-Francois Bastin, estimated there's space for at least 1 trillion more trees, and potentially 1.5 trillion, on top of the estimated 3 trillion trees currently on the planet.

Bastin said reforestation should be the main priority of governments and corporations looking to tackle climate change moving forward. "They should not only focus on it, but this should be a top priority," he told CBS News Friday. 

But it's not a be-all and end-all solution — Crowther said we still need to stop burning oil, coal and gas to tackle the climate crisis. "None of this works without emissions cuts," he said.

And rather than adding trees, in many parts of the world they're being cut down on a massive scale. Deforestation is a major concern in the Amazon, where acres of rainforests are being cut down every day to make room for agriculture. There's as much carbon captured and stored in all the trees of the Amazon as the amount the entire planet has emitted over the past 10 years.

Cut those trees down, and we effectively double the heat-trapping gases of the past decade. So while reforestation may be the best solution, halting deforestation and reducing animal agriculture would also provide immediate benefits. 

"We need to stop deforestation, otherwise we would restore ecosystems for nothing," Bastin said. "The beautiful thing is that it is a universal issue, it can unify us against a common threat, where anyone can have a role to play, by acting on supporting the restoration of ecosystems, but also by changing the way we are living on the planet." 

Stanford University environmental scientist Chris Field, who wasn't involved in the study, told AP its findings make sense but acting on it wouldn't be easy.

"The question of whether it is actually feasible to restore this much forest is much more difficult," Field said in an email.

BBC News reports other scientists were even more skeptical.

"Restoration of trees may be 'among the most effective strategies', but it is very far indeed from 'the best climate change solution available,' and a long way behind reducing fossil fuel emissions to net zero," said Professor Myles Allen from the University of Oxford.

And Professor Martin Lukac from the University of Reading said, "Planting trees to soak up two-thirds of the entire anthropogenic carbon burden to date sounds too good to be true. Probably because it is."