Cooling trend

The global warming debate heated up again on Feb. 2 when the Intergovernmental Panel on Climate Change (IPCC) concluded that warming is "unequivocal" and that human activity is "very likely" the cause of increasing temperature, melting ice caps, and rising sea levels. The fourth IPCC report capped a solid month of publicity and momentum for the global warming movement:

First the internet buzz about drowning Arctic polar bears and premature cherry blossoms in Washington, D.C.-never mind the bitter cold snap that descended on the capital last week.

Then a nod to global warming in the State of the Union, a Nobel Peace Prize nomination for An Inconvenient Truth's Al Gore, and House oversight hearings to investigate purported suppression of climate science research.

Now this pronouncement from the UN-chartered panel-touted as the leading international network of climate scientists-that greenhouse gases produced by human activity are the main causes of increased global temperature since 1950.

So is the case for global warming already open and shut?

Yes and no, according to Kevin Vranes, a climate scientist at the University of Colorado, who made the news last month by blogging about global warming "tension" in the academic community.

"Nobody that is what I would call a reputable climate scientist doubts that there is climate change, that there has been global warming, and that we are the main cause of it," said Vranes, who was quick to clarify his agreement with mainstream premises. "The main question is about the future. . . . Our predictions of the future have some significant uncertainties in them."

How significant is that uncertainty? Possible scenarios range from the apocalyptic "we're all going to die," to "[not] that big of a deal," and everything in between.

After attending an American Geophysical Union meeting, Vranes mused about an "internal backlash" in a Dec. 20 post on his "No Se Nada" blog. "[W]e're wondering if we didn't create a monster," Vranes wrote. "We wonder if we've oversold the science."

In a push to quantify future predictions and fight the perception of subjectivity, the IPCC panel elevated its confidence level that humans cause global warming from "likely"-66 percent probable-in the 2001 report, to "very likely"-90 percent probable-in the 2007 report.

But the document that generated international headlines did not exhaustively detail the evidence for the new rating. Instead, a 21-page "Summary for Policymakers" announced the findings of the panel in a policy report composed of equal parts text and colorful graph. The thick and technical scientific report will not be available until May.

To skeptics like Viscount Christopher Monckton, this "strange separation" raises the possibility that the summary, written by political representatives of governments, "will be taken as a basis for altering the science chapters," written by the scientists themselves.

According to IPCC spokesman Kristen Averyt, the major reason for the separate publication dates is "copy editing."

"We have to make changes in the scientific report to be consistent with the 'Summary for Policymakers,'" she said, but stressed that the changes are completely public.

Monckton, a former British journalist and policy advisor to Margaret Thatcher, also pointed to revisions in key variables as evidence that UN computer models had exaggerated previous global warming statistics. In the 2001 report, for example, the high-end estimate of sea-level rise by the year 2100 was nearly three feet. In the 2007 report, the high-end estimate of sea-level rise was quietly cut nearly in half, down to 17 inches.

Vranes disputed Monckton's analysis of the revised numbers, noting that 17 inches is still significant and that science is an "iterative" process. But if science is inherently iterative, requiring measurement and repetition, why are public predictions about global warming made with such certainty?

"I don't know why climate change is expressed in unambiguous terms," Vranes admitted, before tossing the gauntlet right back. "I think the media does that more than the scientists do."