Ecology, Climate Change and Related News

Conservation Science for a Healthy Planet

New estimate of how much humans have transformed the planet; habitat restoration of degraded lands is key to sequestering carbon and reversing climate change

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by Chris Moony Dec 20 2017  see full Washington Post article

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, Erb 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. (The mass is greater due to the addition of oxygen molecules.)

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. … “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….

….The research means that so-called degraded land — not fully deforested but not “natural” or whole, either — is a phenomenon to be reckoned with.

“It suggests that the amount of carbon released to the atmosphere from land use is approximately equal to the amount still retained,” said Tom Lovejoy, an ecologist at George Mason University who was not involved in the work. “That means the restoration agenda is even more important than previously thought and highlights the enormous amount of degraded land in the world.”…

….“Scenarios that limit global warming to 1.5 or 2 degrees [Celsius] require not only rapid cessation of greenhouse gas emissions but also removal of somewhere between about 100 and 300 billion tons of carbon [or 370 to 1110 billion tons (Gt) of CO2e] from the atmosphere,” Phil Duffy, president of the Woods Hole Research Center, said in an email.

This paper suggests that restoring vegetation around the world could in principle achieve that,” Duffy continued, noting that if all the potential vegetation were restored it would offset some 50 years of global carbon emissions. While “the full theoretical potential will never be realized in practice … this paper indicates that restoring vegetation could make an extremely important contribution to controlling global climate change.”

Karl-Heinz Erb et al. Unexpectedly large impact of forest management and grazing on global vegetation biomass. Nature  Dec 2017 doi:10.1038/nature25138
 
 Abstract: Carbon stocks in vegetation have a key role in the climate system. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of
carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53–58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42–47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.

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