Planting more than 500 billion trees could remove around 25 percent of existing carbon from the atmosphere, a new study has found. What's more: there's enough space to do it.

The study, published in Science Friday, set out to assess how much new forest the earth could support without encroaching on farmland or urban areas and came up with a figure of 0.9 billion hectares, an area roughly the size of the U.S., BBC News reported. That makes reforestation "the most effective solution" for mitigating the climate crisis, the researchers concluded. "Our study shows clearly that forest restoration is the best climate change solution available today and it provides hard evidence to justify investment," senior study author and ETH-Zürich Professor Tom Crowther said, as BBC News reported. "If we act now, this could cut carbon dioxide in the atmosphere by up to 25 percent, to levels last seen almost a century ago." The new trees would remove around 200 gigatonnes of carbon, or two thirds of what humans have pumped into the atmosphere since the industrial revolution.

New report reveals #reforestation is one of the most effective strategies for #ClimateChange mitigation.



We must plant more trees🌲🌳, support restoration organisations and invest wisely.



>> https://t.co/2cGVl73Tz1#TreePotential pic.twitter.com/JFNbDeE42v — Crowther Lab (@CrowtherLab) July 4, 2019

However, the researchers emphasized that tree planting was not a replacement for reducing greenhouse gas emissions or phasing out the use of fossil fuels. "None of this works without emissions cuts," Crowther told Time. Even if tree planting began today, it would take 50 to 100 years for the new trees to soak up those 200 gigatonnes of carbon, he told The Guardian. And, as National Geographic pointed out, the researchers found that potential tree-planting land could shrink by one-fifth by 2050 even if global temperature rise is limited to 1.5 degrees Celsius above pre-industrial levels, as some tropical areas could grow too hot to support forests. Even so, Crowther said tree planting was an important means of immediate climate action. It's "a climate change solution that doesn't require President Trump to immediately start believing in climate change, or scientists to come up with technological solutions to draw carbon dioxide out of the atmosphere," Crowther told The Guardian. "It is available now, it is the cheapest one possible and every one of us can get involved." Assistant-Director General at the UN Food and Agriculture Organization René Castro praised the study's utility. "We now have definitive evidence of the potential land area for re-growing forests, where they could exist and how much carbon they could store," Castro said, as The Guardian reported.