After four years of work, it took the U.N. Intergovernmental Panel on Climate Change until 5 a.m. on the morning of publication last Friday to agree on the final wording of its new report. Agreement was only reached at the end of an all-night closed session at which delegates from governments cross-questioned the scientists and at times sought to put their own spin on the findings. It is not called an "intergovernmental panel" for nothing, and every last nation had to agree to the text before it was published.
Leaving aside the hysterical fringes, most mainstream media coverage of the IPCC report took one of two lines. Some concentrated on its "stark warning" about how scientists are "more sure than ever" about climate change and humanity's role in it. Others more skeptically stressed that the panel had confirmed for the first time a slowdown in warming in the past 15 years, and that, partly as a result, it had slightly lowered its projections of future warming.
Both stories are true. As Thomas Stocker of the University of Bern, the co-chair of the scientists behind the report, put it at the press launch: "Human influence on the climate is clear," and "climate change is the greatest challenge of our time." The assessment had concluded that scientists are now 95 percent certain that the warming since 1950 is due primarily to human activity, up from 90 percent in their last report in 2007.
Yet Stocker also talked about scientific interest in what lay behind what he termed the "hiatus" in warming. Nobody, the report says, is yet sure whether it is a blip - perhaps caused by some natural redistribution of heat between the atmosphere and the oceans - or whether it means climate models have got something wrong about global warming.
But there is a third narrative about the IPCC that has received less attention. Some of those involved in the report process believe the natural caution among scientists - coupled perhaps with a wish not to repeat some exaggerations that marred some previous IPCC reports, and the effect of politicians looking over their shoulders - has created a report that is overly conservative, even biased, in its conclusions. Rather than lowering its expectations of warming, these scientists say, perhaps the panel should be raising them.
Some "scary scenarios" arising from possible positive feedbacks - in which nature amplifies man-made warming - have been left out of the model projections on which the IPCC's headline forecasts are based. Surely, some critics say, it is the scary scenarios that politicians need to know about if they are to do their duty under the UN climate change convention and act together to prevent "dangerous climate change." Even the U.S. signed that, under George Bush senior in 1992.
The report's headline conclusions include:
- Global warming is "unequivocal." The last three decades were the warmest in the atmosphere for at least 1,400 years. While atmospheric warming has slackened unexpectedly in the past 15 years, it continues, and warming is unabated in the oceans. This oceanic warming is melting ice on land and at sea, most notably with the dramatic summer declines in Arctic sea ice. The melting of land ice and thermal expansion mean that sea-level rise is now twice the average rate before 1993, at over 3 centimeters a decade. This too is unprecedented in recent times.
- The warming slowdown is one reason for a marginal reduction in expected warming over the coming century. Modelers now expect a doubling of greenhouse gas concentrations in the atmosphere to bring warming somewhere between 1.5 and 4.5 degrees Celsius, rather than the between 2 and 4.5 degrees projected last time.
- New research identifies clear evidence of an intensification of the water cycle, with wet areas and seasons becoming wetter, and dry areas and seasons drier. But the IPCC has retreated on some statements made in 2007 that this is creating more droughts, or more hurricanes.
The vast tome, which will come to over 3,000 pages, was written by more than 250 authors, reviewed by over 1,000 other experts, and cites more than 9,000 pieces of peer-reviewed science. And yet, in places, the scientists had to work hard last week to restrict political interference with the findings.
Hence that 5 a.m. finish last Friday. Yale Environment 360 has established that the meeting of scientists and government delegates called to sign off on the report was virtually done at midnight on Thursday, when they got to a final paragraph about something the IPCC had not mentioned in previous reports, but which the scientists felt was hardly contentious.
Their draft of the summary report said that, since much of the carbon dioxide emitted into the air by human activity stays there for many centuries, the warming it produces is "irreversible on a human timescale" - at least without massive geo-engineering. Therefore, if the world is serious about restricting warming to below two degrees Celsius since pre-industrial times, it needed in effect to impose a carbon budget. It had to restrict total man-made emissions forever to below about one trillion tons of carbon - or to 800 billion tons if we assume that our emissions of other greenhouse gases are unlikely to halt anytime soon. We are already two-thirds of the way there, at around 530 billion tons.
That was the bald scientific calculation. But three governments in particular objected to this statement. According to sources who attended the meeting, they were China, Brazil and Saudi Arabia. The U.S. was not involved.
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