Nature's carbon 'sink' smaller than expected

Earth in 2100 could be up to 2.7 degrees F. hotter than previously predicted, studies say.

By Peter N. Spotts | Staff writer of The Christian Science Monitor

from the May 3, 2007 edition

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When it comes to global warming, nature's help is limited.

While the continents and oceans have absorbed much of the carbon dioxide that humanity has pumped into the atmosphere so far, they won't be able to keep up with the expected rise in greenhouse-gas emissions over the next several decades. Indeed, some recent studies suggest that current scientific estimates about natural absorption are too optimistic: Earth's climate by century's end could be on average up to 1.5 degrees C (2.7 degrees F.) hotter than current "business as usual" projections suggest.

What this implies is that policy and technological measures to cope with climate change will become even more important. This week, scientists and government negotiators are wrestling over those measures in a key international meeting in Bangkok, Thailand. They will lay out their recommendations in a summary statement slated for release Friday.

"We've been getting a free ride from forests and oceans," says Robert Jackson, a Duke University ecologist who heads the southeastern division of the US Department of Energy's National Institute for Climate Change Research. But "I'm not confident – especially as our fossil-fuel emissions continue to grow – that we can rely on natural systems to bail us out of this."

To be sure, few if any in the climate-policy community advocate a hands-off, let-nature-do-it-all approach. But the use of natural "sinks" – oceans, plants, and soil that can hold carbon – is said to appear in the report researchers and politicians are haggling over this week.

The document is a brief policymaker's summary tied to the third of three large volumes published every six years by the United Nations-backed Intergovernmental Panel on Climate Change (IPCC). The first two reports, issued in February and April, focused on the state of climate science and on the effects researchers already are seeing as a result of global warming.

The current volume, by contrast, aims to suggest a target for stabilizing carbon-dioxide concentrations so that global average temperatures in 2100 would only be about 2 degrees C higher than they were before the Industrial Revolution. The volume also describes medium- and long-term approaches that could achieve that goal and lays out estimates of the economic costs and benefits of emissions mitigation. Thus, it is by far the most policy relevant and politically sensitive of the IPCC reports.

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