SOURCE: Washington Post

DATE: December 20, 2017

SNIP: In this age of climate change, we naturally train our attention on all the fossil fuels being combusted for human use — but scientists have long known that what’s happening is also all about the land.

Just as buried fossil fuels are filled with carbon from ancient plant and animal life, so too are living trees and vegetation on Earth’s surface today. Razing forests or plowing grasslands puts carbon in the atmosphere just like burning fossil fuels does.

Now, new research provides a surprisingly large estimate of just how consequential our treatment of land surfaces and vegetation has been for the planet and its atmosphere. If true, it’s a finding that could shape not only our response to climate change, but our understanding of ourselves as agents of planetary transformation.

Using a series of detailed maps derived from satellite information and other types of ecological measurements, Karl-Heinz Erb, the lead study author, and his colleagues estimated how much carbon is contained in Earth’s current vegetation. The number is massive: 450 billion tons of carbon, which, if it were to somehow arrive in the atmosphere as carbon dioxide, would amount to over a trillion tons of the gas.

But the study also presented an even larger and perhaps more consequential number: 916 billion tons. That’s the amount of carbon, the research calculated, that could reside in the world’s vegetation — so not in the atmosphere — if humans somehow entirely ceased all uses of land and allowed it to return to its natural state. The inference is that current human use of land is responsible for roughly halving the potential storage of carbon by that land.

The impact calculation is so large because humans have done far more than just bring about deforestation, which Erb said accounts for about half of the loss of potential vegetation.

“Half of this effect, half of this halving, is already well described,” he said. “This is the deforestation signal. But the other half, in most studies, is completely missing.”

The study found that there are two far-less-recognized components of how humans have subtracted from Earth’s potential vegetation — and that in combination they are just as substantial as deforestation. Those are large-scale grazing and other uses of grasslands, as well as forest “management.” With the latter, many trees and other types of vegetation are subtracted from forests — often the larger and older trees due to logging — but the forests as a whole don’t disappear. They’re just highly thinned out.

“This effect is quite massive, more massive than we expected actually,” Erb said.