The long-awaited Intergovernmental Panel on Climate Change's (IPCC) first report in six years arrives this Friday, a high-profile summary of global warming's scientific status certain to influence attempts to address the threat of a warming world. It also faces criticism before it even gets out of the gate.
Representatives of 195 member nations are meeting in Stockholm, Sweden, this week to approve the release on Friday of a roughly 30-page summary of the scientific evidence for climate change aimed at policymakers worldwide.
"The world is awaiting the outcome of this session with great expectation," IPCC chairman Rajendra Pachauri said in a speech on Monday opening the final review of the summary in Stockholm. Pachauri cited the report's "obvious significance in respect of the current status of global negotiations and the ongoing debate on actions to deal with the challenge of climate change."
In draft versions of the report, scientists said they are "virtually certain" that humanity's fossil-fuel-related emissions drove the warming of the Earth's atmosphere by about 1.44 degrees Fahrenheit (0.8 degrees Celsius) from 1901 to 2010. This 99 percent or better confidence estimate represents a further increase in scientific certainty over the previous IPCC reports released six years ago.
IPCC Under Fire
However, questions about the IPCC's relevance in the face of rapid scientific progress and extreme weather events worldwide have come ahead of the report's release. A recent BBC news story suggested that politicians want a better explanation of a slowdown in the rate of increase in warming seen in the last 15 years. (See "Does 'Global Warming Pause' Debate Miss Big Picture?")
Complaints about a mistaken reference to shrinking Himalayan glaciers in the Nobel Prize-winning 2007 reports triggered a painful review of editorial processes for these latest reports, Pachauri noted in his speech. Some researchers, notably Columbia University's James Hansen, have criticized past IPCC reports for exhibiting a "scientific reticence" or cowardice in their refusal to confront the risks of sudden sea-level rise from melting Greenland or Antarctic ice sheets. In draft versions at least, the new IPCC report does tackle the question of ice sheet loss, finding it "very likely" that melting ice and the expansion of the ocean due to its heating will lead to sea-level rise exceeding that of the last century.
This time, complaints about the summary have already started before its release, with Arthur Petersen, chief scientist at the PBL Netherlands Environmental Assessment Agency, accusing IPCC reports of underplaying both the worst-case and best-case estimates of future warming. "As a result, policymakers and the public are not being fully informed of the worst potential consequences of climate change," he wrote last year.
"I don't see any evidence of that," said climate scientist Gavin Schmidt of NASA's Goddard Institute for Space Studies, which Hansen formerly headed. "IPCC makes predictions, and those are imperfect. Some are going to be under; some are going to be over. That's the best that you can hope for."
Friday's summary will be followed by a 1,000-page technical report on Monday. A second report looking at the impacts of climate change worldwide and a third one examining steps to lessen future effects will come in 2014. Still being written, these massive reviews of the climate science literature will require the work of some 831 scientists and editors, with additional input from other scientists, and result in 7,000 pages of scientific writing.
"Just because there are more alarmist things out there doesn't mean that they are credible," Schmidt said, citing concerns about catastrophic releases of methane from melting permafrost that sparked scientific disagreement this summer. "Just because someone is an outlier doesn't mean that it will be credible and convincing to other people."
Deadlines for considering research in the IPCC reports—a six-month limit—renders them out of date before they are published, noted David Victor of the University of California, San Diego, and the author of Global Warming Gridlock.
The deadline for research to be considered for the Friday and Monday reports, for example, came in March of this year. That was too early to pick up recent findings that link the slowdown in warming's increase seen over the last 15 years to a naturally occurring "cool spot" in the eastern Pacific.
"Yes, there are lots of areas where there are uncertainties, and we all agree that we will never have perfect predictions," said climate scientist Mike MacCracken, former director of the National Assessment Coordination Office at the U.S. Global Change Research Program. But in the big picture, he calls the IPCC reports invaluable. "From a large-picture policy perspective, I think it is helpful to have the scientific community and policy communities come together to indicate what the nations agree to unanimously," he said by email.
"All this comes at a tremendous cost. A tremendous number of scientists have essentially the report as a second job at great cost to their research," Victor said. "Frankly, I have gone back and forth about it for a long time, and I have come to see that there is a tremendous value in having a central statement on how the scientific world sees climate change."
Without the IPCC report, a cacophony of national assessments would compete for relevance in debates about climate change, said Victor, an editor on next year's IPCC climate change mitigation and adaptation report. He admits he ducked such responsibility on the 2007 report, but said he has come to see the effort as an important one in climate policymaking.
"The issue about warming over the last 15 years doesn't have much impact on political and scientific thinking looking ahead," Victor said. "Based on the science going into them, the [next] IPCC reports will have a real impact in offering diplomats a reckoning -- and they don't handle reckonings well -- with the observation that [greenhouse gas] emissions are all following the worst of the worst-case scenarios for the future."
IPCC Good and Bad
For that reason, Victor expresses sympathy for the IPCC's goal of producing average estimates of global warming's effects. Draft reports, for example, foresee a "likely" increase of global temperatures by 0.7 to 1.8 degrees Fahrenheit (0.4 to 1.0 degrees Celsius) by 2035. Such estimates obscure the worst-case scenarios that Petersen warned about.
"The extreme 'low-tail' events are becoming more important for policymakers to think about," Victor said. Some of the scientific literature going into IPCC reports has actually increased uncertainty about our understanding of worst-case scenarios for sea-level rise and other effects. "That means more worry over the extreme situations," he said. He calls for future reports to focus more on "what's new" in climate research rather than restating what is known.
"Ultimately, the IPCC reports are just a gigantic review article written by 1,000 people," Victor said. "Of course it will have some shortcomings as result. But it is very valuable in the end."
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Brian Clark Howard contributed research.