WASHINGTON — More than 3 trillion trees now grow on Earth, seven times more than scientists previously thought. But it’s also trillions fewer than there used to be, a new study concludes.
A United Nations-affiliated youth group had a goal of planting 1 billion trees, and Yale forestry researcher Thomas Crowther was asked whether planting that many trees would do anything to help combat human-made climate change. Trees capture and store heat-trapping carbon dioxide.
Crowther said first he had to figure out how many trees are on Earth and that number was far more than anyone expected: 3.04 trillion trees, according to a study published Wednesday in the journal Nature.
The previous estimate was 400 billion trees, and that rough count was based on satellite images from space. Crowther and colleagues used 429,775 ground-based measurements along with satellite measurements and computer models to get a more accurate figure.
But Earth used to be covered with far more trees. Using computer models, Crowther and colleagues estimated that before human civilization Earth had about 5.6 trillion trees. So the number of trees on Earth has been chopped nearly in half.
Crowther mostly blames people. His study found that 15 billion trees are cut down each year by people, with another 5 billion trees replanted. At that rate, all of the trees will be gone in about 300 years.
“Humans are diminishing that huge population on such a global scale,” Crowther said.
So the planting of a billion trees wouldn’t do too much to fight climate change on its own, Crowther conceded. But he said that didn’t stop the tree planters group; they just upped their goal to 18 billion trees.
