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Earth Can't Soak Up Excess Fossil Fuel Emissions Indefinitely

By the end of the century, the land and ocean may reach their capacity to absorb greenhouse gas from the atmosphere

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Earth’s land and oceans have been soaking up the excess carbon dioxide that humans have pumped into the atmosphere through smokestacks and tailpipes. But there are limits.

A new-generation computer model indicates that the capacity of land and ocean to absorb and store the heat-trapping greenhouse gas will reach its peak by the end of the century. Without that sponge, carbon dioxide could accumulate faster in the atmosphere and accelerate global warming.

“Time is of the essence in dealing with greenhouse gas emissions,” said Scott Doney, a WHOI geochemist and part of a team that created the new computer model to analyze the workings of Earth’s climate system. “We can start to address the issue now, or we can wait 50 years; but in 50 years we will have missed our best opportunity for remediation.”

The team reported its findings in the Aug. 9 issue of the Proceedings of the National Academy of Sciences.

Five years ago, Doney and colleagues—Inez Fung and Jasmin John of the University of California, Berkeley, and Keith Lindsay of the National Center for Atmospheric Research—set out to create a new climate model that included important missing pieces of the puzzle: the roles that living things, ecosystems, and ocean circulation play in cycling carbon around the planet.

The researchers factored in a wide range of complex interactions that affect where carbon goes and where it ends up. These included: how plants on land and sea absorb and release carbon dioxide; how microbes decompose carbon in soil; how differences in forest litter can affect plant respiration—and the effects of temperature, rainfall, soil moisture, cloud cover, ocean salinity, and wind speeds on all these biogeochemical interactions.

The new model casts doubt on the oft-repeated argument that plants and ecosystems will exploit and accommodate excess carbon dioxide indefinitely. That ability ultimately is limited by other factors, such as the availability of water and nutrients, the researchers say. Meanwhile, humans show little inclination to limit their carbon dioxide emissions.

This research was funded by the National Science Foundation, the National Aeronautics and Space Administration, Lawrence Berkeley National Laboratory, and the WHOI Ocean and Climate Change Institute.


Humans are pumping excess carbon dioxide into the atmsophere through industrial smokestacks, car tailpipes, and the burning of forests. Carbon dioxide is a heat-trapping greenhouse gas that most scientists believe is contributing to global warming. (© DigitalVision, Ltd.)

Scott Doney is a senior scientist in the WHOI Department of Marine Chemistry and Geochemistry and a fellow of the WHOI Ocean and Climate Change Institute. (Photo by Tom Kleindinst, WHOI)

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