There is good and bad news about the number of trees on our planet. The good news is that there are seven times more trees than we thought. Until a few years ago, scientists estimated that the world had 400 billion trees. However, a new study estimates that there are around three trillion trees. That's a three followed by 12 zeroes. There are over 420 trees for every person alive today. Dr Thomas Crowther told the BBC that this new number changes nothing. He said: "It's not good news for the world or bad news that we've produced this new number."

The bad news is that thousands of years ago, the earth had six trillion trees. Humans have cut the number of trees in half. An example of this is Europe. It used to be a giant forest. Now much of it is fields and cities. Dr Crowther said people are responsible for the loss of three trillion trees. Another 15 billion trees are lost each year because of deforestation and farmland. The scientists said this figure is "considerably higher" than a century ago. Dr Crowther warned that: "This study highlights how much more effort is needed if we are to restore healthy forests worldwide."