The world today has approximately 3 trillion trees, but scientists say planting a trillion more 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 figure out that there is enough space globally to plant more than a trillion trees, possibly a trillion and a half, 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. 

Russia, the United States, Canada, Australia, Brazil and China have the most available room for reforestation. Rather than adding trees in these areas, trees are being cut down on a massive scale. Deforestation is a major concern in the Amazon for example, 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. 

According to Crowther, “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. 

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.

https://www.cbsnews.com/news/planting-a-trillion-trees-could-be-the-most-effective-solution-to-climate-change/

https://science.sciencemag.org/content/365/6448/76.full

https://apnews.com/8ac33686b64a4fbc991997a72683b1c5