Published December 26, 2015 09:33 AM

How many trees are on planet Earth?

Here is a pop quiz: How many trees are on the planet?

Most people have no idea.

A new study says the answer is more than 3 trillion trees — that's trillion with a T, and that number is about eight times more than a previous estimate.

Thomas Crowther was inspired to do this tree census a couple of years ago, when he was working at the Yale School of Forestry and Environmental Studies. He had a friend who was working with a group with an ambitious goal: trying to fight global warming by planting a billion trees. A billion trees sounded like a lot. But was it really?

"They didn't know if planting a billion trees was going to add 1 percent of the world's trees, add 50 percent of the world's trees," recalls Crowther. "They didn't even know if it was even possible to fit a billion trees on Earth."

So his pal asked him a simple question: How many trees are growing on our planet? "I assumed that this was somewhere out there, it's information that someone will know," says Crowther.

That turned out to be wrong, he says. "Having spoken to a lot of forestry experts, it doesn't seem like anyone had any idea."

There was one estimate based on satellite images: about 400 billion trees worldwide, or 61 trees for every person.

But there were doubts about that number because another recent estimate, based on ground-truthed measurements, found 390 billion trees in the Amazon basin alone.

Trees image via Shutterstock.

Read more at NPR.

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