How many trees are there on earth? A lot … or, more precisely, 3.04 trillion (about 422 per person on the planet, CNN notes). That's what some scientists discovered this year after conducting a global tree census, NPR reports. To put that number in context, it would take some 96,000 years to plant 3 trillion trees, if you were planting a tree per second, says ecologist Thomas Crowther, who led the study while working at Yale University. A previous estimate, based on satellite images, had the world's tree population at about 400 billion—some 7.5 times less than the new estimate, which was published September in the journal Nature. "It's a huge, astronomical number that I don't think I could comprehend before this study," Crowther tells NPR.
Still, Crowther cautions, "It's not like we discovered new trees," so it's not time to say, "There's plenty left. No worries." In fact, per Nature, the researchers think the total number of trees has been slashed nearly 50% in the last 12,000 years. And about 15 billion trees are cut down each year. The tree census involved getting tree counts in certain areas from people on the ground, using existing forest inventories, and entering the data into computer models. The whole thing started when Crowther's friend, part of the Billion Tree Campaign, was trying to figure out what kind of impact planting a billion trees would have. He asked Crowther how many trees are on the earth. At the time, Crowther tells NPR, "It doesn't seem like anyone had any idea." Now they do … and the information could be used to weigh whether trees should be preserved, rather than cut down to make way for farms, a Stanford University ecologist tells Nature. (Droughts might be even worse for trees than we thought.)