 images. Another, based on ground-truthed measurements, suggested there were 390 billion trees in the Amazon basin alone. And thus, Crowther’s mission was set. He knew there was a method to get better numbers, and so he did. "We used ground-sourced information," says Crowther. "All of the information that went into our models was generated from people standing on the ground counting numbers of trees in a given area. And so we could relate this information to what the satellites are telling us." To further fine-tune the numbers, his team also relied on detailed forest inventories that a number of countries have produced. "It definitely couldn't have been done without all of those huge national forest inventories and thousands of people going out, collecting tree information around the world," says Crowther. Compiling information from around 400,000 forest plots, the researchers meticulously crunched countless calculations and fed the data to a computer, which arrived at the number. "We all gathered in a room, it was a very exciting time," remembers Crowther. "We'd been working toward it for two years." The result: A staggering three trillion trees. Three trillion trees! It’s a number so huge that it becomes abstract; it almost goes in one ear and out the other. But consider this, three trillion seconds equals 94,638 years. He says the number astonished them, and also caused a bit of concern. "My fear is that a lot of people might think, 'OK, well, there's loads of trees, so who cares about the environment, there's plenty left! No worries!' What I'd highlight is that it's not like we've discovered new trees," he says. "We've just generated a new number that will help us to understand the global forest." Compared to the time before human civilization took over the planet like the crazy invasive species that we are, there were twice as many trees. He notes that the gross number of trees lost annually because of humans is now about 15 billion. As for friend-guy who asked the question in the first place, did the tree tally have an effect on the aim of the tree-planting campaign? "Based on this, they really want to upscale their efforts hugely," says Crowther, who says that the new count has amped up their efforts. "Their goal is now to plant a trillion trees." Translated to seconds? That would be 31,546 years.