More trees than thought - but fewer than ever

In a blockbuster study released Wednesday in Nature, a team of 38 scientists finds that the planet is home to 3.04 trillion trees, blowing away the previously estimate of 400 billion. That means, the researchers say, that there are 422 trees for every person on Earth.

However, in no way do the researchers consider this good news. The study also finds that there are 46 percent fewer trees on Earth than there were before humans started the lengthy, but recently accelerating, process of deforestation.

"We can now say that there's less trees than at any point in human civilization," said Thomas Crowther, a postdoctoral researcher at the Yale School of Forestry and Environmental Studies who is the lead author on the research. "Since the spread of human influence, we've reduced the number almost by half, which is an astronomical thing."

In fact, the paper estimates that humans and other causes, such as wildfires and pest outbreaks, are responsible for the loss of 15.3 billion trees each year - although the authors said at a news conference that perhaps 5 billion of those may grow back each year, so the net loss is more like 10 billion annually.

It's important to note that the study's estimates critically rely on the definition of "tree" - the study calls it a woody plant that, at breast height, has a stem that is at least 10 centimeters in diameter.

The new research suggests that massively more trees need to be planted than previously thought - but Crowther said he thinks that will only inspire activists to redouble their efforts.

The nation with the single largest number of trees was Russia, with 641 billion, and 4,461 trees per person based on 2014 population estimates - statistics underscoring the vastness of Siberia's boreal forests.

The U.S. had 319 million people in 2014, but 228 billion trees. That's 716 trees per person. Brazil had 301 billion trees (1,494 per person), Canada 318 billion (8,953 per person), and China 139 billion (102 trees per person). Among highly populous countries, India (population, 1.267 billion) had a tree population of only 35 billion, leading to just 28 trees per person.

The new Nature study has myriad implications, but some of the largest are for the problem of global warming.

Trees pull carbon dioxide out of the atmosphere as they grow, and cutting or burning them down releases that carbon again. So that means that deforestation is making global warming worse - and it also means that if we were living on an Earth with close to 6 trillion trees, rather than 3 trillion, climate change would be less severe.