IPCC’s New Emphasis on Risk May
Signal Broad Shift in Climate Thinking

A tipping point in the debate over global warming came in 2007, and the world’s news media were abuzz about it. That November, government delegates from almost all of the world’s nations, meeting in Valencia, Spain, came to a consensus on the wording of a 25-page climate change report titled “Summary for Policymakers.” That summary for the world’s leaders would accompany the fourth and latest round of analysis from scientists and other experts from the Intergovernmental Panel on Climate Change (IPCC).

Participants in a famously cautious process were finally ready to say not only that climate change was a reality, but that human activity is almost certainly at its root. (That same year, the Intergovernmental Panel on Climate Change shared the Nobel Peace Prize with former Vice President Al Gore.)

Echoing language from the scientific assessment, the summary for the world’s political leaders for the first time bluntly exclaimed that “warming of the climate system is unequivocal. … Most of the observed increase in global average temperatures … is very likely due to the observed increase in anthropogenic GHG [greenhouse gas] concentrations.”

Considering that representatives of even long-reluctant nations concurred, including the United States under the Bush administration, the forcefulness of the conclusion was news indeed. But another profound paradigm shift that went unnoticed also may have begun as early as the November 2007 Valencia meeting, according to Gary Yohe, a visiting professor of economics at F&ES this year and Woodhouse/Sysco Professor of Economics at Wesleyan University.

Neither the scientists who prepared the assessment nor the national delegates who approved it would likely put it this way, but at Valencia a new appreciation for the perils of playing de facto global Russian roulette had quietly (and some concerned scientists and environmental activists would add finally) entered the picture. A hint lies deep in the policymaker summary. On its final page comes a firm recommendation that something called “iterative risk management” become key to understanding and confronting climate change.

The need for managing risk might seem obvious, but according to Yohe, one of the 40 international IPCC co-authors of the draft on which the new summary was based, risk in all its dimensions had not been emphasized in previous IPCC summaries as a lens through which policymakers might view the problem.

The purpose of the summary, says Yohe, had always been to present “policy-relevant knowledge” to political leaders, forming a foundation on which policymakers would prescribe laws, regulations and treaties. But past IPCC summaries had focused primarily on those climate change projections that nations agreed unanimously were most likely.

He says, “The process had previously allowed only high-confidence conclusions to find their way into the policymaker summaries.” The problem with that, he notes, is that the world’s policymakers were not presented with a thorough picture of both what was likely to happen and what could happen, including Russian roulette-style low-probability, but catastrophic-consequence, scenarios.

From today’s perspective, the highly likely consequences of global warming might seem bad enough. Working with some of the most recent scientific data, a December 2008 study prepared by the U.S. Geological Survey noted that the newest information not only suggests that such problems as increases in sea levels, much of it purely through physical expansion as seawater heats up, and increasing drought in the American Southwest were highly likely as the world moved through the current century, but also that past calculations had underestimated how severe some of these likely problems would be. As IPCC reports have noted, the likely ranges of sea level rise alone could mean inundation of vast areas of inhabited coastline, putting at risk whole cities and regions as well as some low-lying nations.

Problems that are less likely but even more dire could include the collapse, decades to centuries in the future, of the vast ice sheets of Greenland and Antarctica. That could lead to such devastating increases in sea levels that they would be measured in multiple meters.     

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