The case for reducing emissions of greenhouse gases is more compelling than ever.
But it's also past time to begin drawing carbon out of the air.
About the time this article is published, the nations of the world will be gathered in Copenhagen to discuss ways to reduce emissions of carbon dioxide and other greenhouse gases (GHGs). In the run-up to Copenhagen, the general expectation had been that this meeting would at last chart an effective international climate-change policy to succeed the Kyoto Protocol. But expectations have moderated as 2009 progressed, and the common wisdom now is that the most likely outcome is a framework understanding with an extended working-out period to follow.
In many ways, this is all too familiar: year after year of presentations and negotiations while GHG emissions continue to rise and the scientific evidence paints an ever-more dire picture. Severe changes in the biosphere, such as the dramatic retreat of Alpine glaciers, are already occurring with atmospheric GHG concentrations at the current level of about 388 parts per million (ppm); they continue to rise about 2 ppm per year. The momentum built into the processes driving climate change virtually guarantees worse to come, even with significant cuts in emissions. To prevent the severest outcomes, it looks like we'll have to augment whatever progress on energy emissions and forest incentives comes out of Copenhagen with new ecosystem-based initiatives to pull carbon out of the atmosphere--an effort that, in effect, will amount to recarbonizing the Earth.
What GHG level should we aim for? The science is still evolving, but many important policy positions and discussions peg the acceptable upper bound at about 450 ppm, which would theoretically limit further temperature increases to an additional 1.25 degrees Centigrade above current levels (and about 2 degrees C above pre-Industrial temperatures). However, NASA's top climate scientist, James Hansen, has been outspoken in advocating a maximum of about 350 ppm. "Humanity's task of moderating human-caused global climate change is urgent," Hansen and several colleagues wrote in a widely cited 2008 paper. "[T]here is a danger that human-made forcings could drive the climate system beyond tipping points such that change proceeds out of our control." Most critically, the Antarctic and Greenland ice sheets could melt and northern permafrost zones might warm and release their methane, triggering cascading ecological catastrophes.
Other assessments broadly support Hansen's target. For instance, climate activist and biologist Tim Flannery of Australia's Macquarie University points out that the findings of the Intergovernmental Panel on Climate Change (IPCC) support the essence of the Hansen et al. 2008 paper: "We are tracking the worse-case scenario of the IPCC's Third Assessment Report. ... This indicates that catastrophic climate change will be unavoidable if emissions continue to grow. ... Key indicators of this include ... the rate of warming ... and the rate of sea-level rise. ..."
"We are seeing abrupt changes, [such as] coral bleaching in the oceans and the pine bark beetle conifer mortality on the land," says biologist and Heinz Center Biodiversity Chair Thomas Lovejoy. "That is with only three-quarter degree of warming. At 450 ppm it is two degrees of warming. ... [I]t seems a real mistake to go beyond 350 ppm." Flannery, Love-joy, and United Nations Environment Programme (UNEP) Executive Director Achim Steiner called last year for bolstering ecosystems to lower GHG concentrations. Alongside "the imperative to redesign the energy base of human societies," they write that "the potential to remove [CO.sub.2] from the atmosphere by restoring biodiversity and carbon is clearly of major consequence." In short, this is a call for planetary engineering, and Lovejoy believes the only guaranteed safe way to do this is "biological ... because all life is built of carbon."
Soil scientist Rattan Lal, director of Ohio State University's Carbon Management and Sequestration Center, has written extensively on natural ecosystem responses that would lower greenhouse gas levels. According to Lal, about 478 gigatons (1 gigaton equals 1 billion tons) of carbon have been released from land uses since the beginning of agriculture, while fossil fuels have released around 292 gigatons of carbon from 1750 to the present. Therefore, Lal argues, "recarbonization of the planet has a technical maximum potential of sequestering...