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Bombshell: Land, ocean carbon sinks are weakening, making climate action more urgent

One of several huge craters recently found in Sibera. They are “probably caused by methane released as permafrost thawed.” Global warming is projected to turn the tundra into a net source of carbon emissions by the 2020s.
Joe Romm, Climate Progress, 23/03/15

We are destroying nature’s ability to help us stave off catastrophic climate change. That’s the bombshell conclusion of an under-reported 2014 study, “The declining uptake rate of atmospheric CO2 by land and ocean sinks,” as coauthor Dr. Josep (Pep) Canadell recently explained to me.

Based on actual observations and measurements, the world’s top carbon-cycle experts have determined that the land and ocean are becoming steadily less effective at removing excess carbon dioxide from the atmosphere. This makes it more urgent for us to start cutting carbon pollution ASAP, since it will become progressively harder and harder for us to do so effectively in the coming decades.

As Canadell put it, “clearly Nature is helping us” deal with atmospheric CO2 right now much more than it will be decades to come. He said this was one more reason why delaying action to cut carbon pollution is a costly and dangerous mistake.

 

Canadell is executive director of the Global Carbon Project, a project by the international scientific community to “to develop a complete picture of the global carbon cycle, including both its biophysical and human dimensions together with the interactions and feedbacks between them.” Canadell notes that this paper includes co-authors who were previously skeptical that there was “a decreasing long-term trend in the carbon sink efficiency over the last few decades.”

Because this is one of the most consequential recent findings by climatologists, with significant policy implications, I’ll examine it in more detail.

The ocean and the land (including vegetation and soils) are carbon “sinks” that currently absorb more than half of all human-caused carbon dioxide emissions. Scientists have long been concerned that these sinks will become increasingly ineffective at absorbing CO2 — because of global warming itself. That would mean a greater and greater fraction of human-caused carbon pollution would stay in the air, which would speed up climate change, causing even more CO2 to stay in the air — an amplifying feedback. And that in turn means humanity will have to work harder and harder in the future to keep CO2 and methane from accumulating in the air.

For instance, the defrosting permafrost and the resultant release of carbon dioxide and methane (CH4) turns part of the land sink into a source of airborne greenhouse gases (with methane being much more potent at trapping heat than CO2). Similarly, as global warming increases forest and peatland fires — burning trees and vegetation — that also turns one part of the land carbon sink into a source of atmospheric CO2.

In September 2014, the World Meteorological Organization (WMO) reported:

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