Friday's release of a much-anticipated report on global warming from the UN's Intergovernmental Panel on Climate Change (IPCC) in effect asks a profound question of humanity: What do you want your climate to look like over the next several centuries – and probably longer?
The report states in unequivocal terms that the climate is warming globally and that since the middle of the 20th century, human industrial activity – the burning of fossil fuels and, to a lesser extent, land-use changes – is warming's main driver. Since the last report in 2001, confidence in that statement has risen from "likely" (greater than a 66 percent chance) to "very likely" (greater than 90 percent).
But beyond detailing current and projected effects of warming – including sea-level rise, vanishing alpine glaciers, and increases in severe-weather events – the report hints at the need for a conscious control over the environment and a unity of purpose that humans have yet to achieve on such an enormous scale.
"When people think about climate impacts, they think about something very narrow: What icky things are going to happen where I live?" says Jerry Mahlman, a senior research associate at the National Center for Atmospheric Research in Boulder, Colo. "They don't say: What's going to happen to the poor Bangladeshi farmers who get hit with a triple whammy" – rising sea levels, more intense tropical cyclones, and reduced supplies of fresh water. "Everyone wants to talk about their particular piece of turf. But this is a problem that is intrinsically and fundamentally global."
The new report, which focuses on the science of climate change, is the first of three main volumes the IPCC will release this year, plus a final "synthesis report." The document the IPCC unveiled Friday (available at ipcc.ch) in Paris is the first volume's short form – the summary for policymakers.
The report already is prompting calls for more-concerted action to reduce carbon-dioxide (CO2) emissions.
Noting that representatives from 113 governments – including the United States – signed off on the summary's conclusions, Yvo de Boer, executive secretary of the UN's Framework Convention on Climate Change, added, "Any notion that we do not know enough to move decisively against climate change has been clearly dispelled.... The world urgently needs a new international agreement on stronger emissions caps for industrialized countries, incentives for developing countries to limit their emissions, and support for robust adaptation measures."
In France, President Jacques Chirac called on the UN to replace the UN Environment Program with an agency that would be "an instrument for evaluating ecologicial damage and how to remedy it."
And in Washington, the report is likely to add considerable momentum to various bills in Congress aimed at reducing US CO2 emissions using a mandatory cap-and-trade approach – something that has been anathema to the Bush White House. Although the issue earned a brief mention in his State of the Union address as a serious problem, the president made no mention of the IPCC report or of global warming in general in a radio address Saturday.
On Thursday, however, the House Committee on Science and Technology is set to hold Capitol Hill's first formal hearings on the report. Some analysts suggest that the evidence in the IPCC report could make it difficult for Mr. Bush to justify a veto if any bills come to his desk before his term ends.
Among the report's projections:
• Temperatures are "likely" to rise 2 degrees to 4.5 degrees Celsius by the end of the century, if CO2 concentrations reach twice their preindustrial level. Within that range, the most likely result is 3 degrees C (5.4 degrees Fahrenheit). That additional warmth will distribute itself unevenly, with the highest increases in the Arctic and progressively smaller increases farther south.
• Sea levels could rise by century's end from 28 to 58 centimeters (11 to 23 inches) above 1999 levels globally. That's a narrower range than the IPCC offered in 2001, when it projected a range of 9 to 88 centimeters. Even if CO2 concentrations could be stabilized at twice preindustrial levels by 2100, thermal expansion of the oceans alone could raise sea levels an additional 1 to 3 feet by 2300. But recent research also suggests that the Greenland ice sheet is losing mass faster than expected, leaving open the possibility that sea-level increases will be higher if the melting trend continues to accelerate. If Greenland's ice cap continues to lose mass over the next 1,000 years, the entire ice cap would vanish, raising sea levels by some 23 feet.
Overall, because carbon dioxide remains in the atmosphere for hundreds of years and a substantial part of the heating is "banked" in the oceans, the report holds that between past and future CO2 emissions, the climate will warm and sea level will rise for more than 1,000 years.
Policymakers face several challenges in trying to deal with the issue, beyond its longer-than-an-election-cycle time frame. The first is its sheer magnitude. Many climate scientists agree that emissions already are on track to double by century's end, perhaps sooner.
Under a "business as usual" approach, which in part assumes today's rate of innovation, the world would have to slash emissions by 70 to 80 percent this century to reach an often-talked-about CO2 concentration target of 450 parts per million by 2100. Over the long term, stabilizing CO2 concentrations in the atmosphere means reducing emissions close to zero.
While current legislative efforts at the state and local level represent a start, they merely "sandpaper the edge off of a catastrophe," Dr. Mahlman says.
A crucial step forward would be to agree on a clear target for stabilizing CO2 concentrations, notes Gerald Stokes, a vice president with Battelle Memorial Laboratories and a former chief scientist for the US Department of Energy's Atmospheric Radiation Measurement program.
Setting emissions targets isn't enough, he says. With a firm target that means something from the atmosphere's perspective, policymakers are in a better position to determine the technological path countries will need to follow, as well as put a firm economic value on carbon dioxide so the costs and benefits of mitigation – and of delay – can be more accurately assessed.