Trying to Plant a Trillion Trees Won’t Solve Anything
Only a monster would say no to this pitch: The best way to beat climate change - the warming of Earth caused by gases like carbo dioxide emitted by human industry, leading to rising sea levels, worsening fires and storms, drought and disease – is simple. Plant a trillion trees. It’d be “one of the most effective carbon drawdowns to date,” said an article on the idea in the journal Science this past summer. And who doesn’t love trees, right?
Except the math turned out to be a little shady. Last month a bunch of climate scientists and ecologists piled onto that tree research in the same journal, calling out numerous errors in the first team’s calculations. At about the same time, a whole other bunch of ecologists started pushing back on the agriculture - tech startup Indigo for pitching a similar land-based carbon sequestration strategy, the “Terraton Initiative”, paying farmers to use new methods that could suck down a trillion metric tons (a teraton) of carbon. These goals are critical and the ideals are noble - who doesn’t want to stop climate change? Pretty much everyone except the US government agrees on that. It’s the numbers that are the problem. Take the trees thing. The scientists who proposed it made careful maps of where trees grow today, all over the planet. They had a census of how many were there, combined with satellite data, all used to estimate how many potential trees could grow - and how much carbon those trees would slurp out of the atmosphere, a nontrivial calculation. There’s room for 0.9 billion hectares of new trees, they said - 2.2 billion acres of tree cover, which draws down 205 metric gigatons of carbon, or 225 billion tons in US non-metric. That’s in line with the goal of keeping warming at or below 1.5 degrees, per the Intergovernmental Panel on Climate Change. World: saved! But then the bills started coming due. The team forgot that 55 percent of all historically emitted carbon got absorbed by the oceans, not the land, and so underestimated the total amount of carbon by about one half. They overestimated carbon uptake by trees, and suggested putting trees where they’ve never been, or where they’d actually make the planet hotter (by darkening planetary albedo over icy, more reflective terrain). They didn’t take into account that the ecosystems where they wanted to plant trees already sequestered carbon. And so on. “We’re not talking about small errors here. We’re talking about a huge difference in the total amount of carbon you could sequester,” says Carla Staver, an ecologist at Yale University.
(Adam Rogers, www.wired.com, 25/10/2019)
A tradução mais adequada para o trecho do último parágrafo: “the bills started coming due” é:
