When you're a scientist trying to count every tree on the planet, you need to prepare yourself for some good-natured ribbing.
"It's transformed almost every one of my conversations with anyone," said Tom Crowther, a scientist with the Netherlands Institute of Ecology and the Yale School of Forestry and Environmental Studies. "At some point it comes up, and we say things like, 'Yeah, so how many trees do you think are in the world?' People don't even know where to begin guessing," he said, "but the jokes always then start, where people go, 'Oh well, did you get that one? Yup, the one outside my garden just fell over, so you're probably wrong."
To try and count every tree on earth, Crowther looked at more than 400,000 official tree counts done by foresters all around the world, comparing those numbers with pre-existing satellite imagery. From there, he was able to crunch numbers in a computer and, eventually, create an estimate of the world's tree population. The results were published in the journal Nature.
"The total number, once we added up all our pixels, all of our areas, was close to about 3.041 trillion trees," Crowther said, about eight times more than the previous worldwide estimate of 400 billion.
Still, Crowther said, "It's not like we've discovered a whole load of new trees. We've not discovered more carbon or any different impacts on the climate," he continued. "All we've done is categorize the global forest using a robust method that, hopefully, can generate numbers that scientists and environmental practitioners can use."
Crowther said he recognizes the numbers are all estimates. And in a places like Connecticut, or large swaths of Europe, where there are a lot of young forests with smaller trees, he said its harder to get an accurate count.
Going forward, Crowther hopes his data will allow ecologists to better understand how losing trees can impact carbon concentrations in the atmosphere -- a crucial piece of knowledge in the fight against global warming.
In case you're curious: as of 2014, the USDA Forest Service estimates there are nearly 790 million trees in Connecticut.
