Climate Change 2007: The Physical Science Basis: Summary for Policymakers
When the Intergovernmental Panel on Climate Change (IPCC) issued its latest report in early February, it was greeted with shock: “World Wakes to Climate Catastrophe,” reported an Australian paper. But global warming is by now a scientific field with a fairly extensive history, and that history helps set the new findings in context—a context that makes the new report no less terrifying but much more telling for its unstated political implications.
Although atmospheric scientists had studied the problem for decades, global warming first emerged as a public issue in 1988 when James Hansen, a NASA scientist, told Congress that his research, and the work of a handful of other scientists, indicated that human beings were dangerously heating the planet, particularly through the use of fossil fuels. This bold announcement set off a scientific and political furor: many physicists and chemists played down the possibility of serious harm, and many governments, though feeling pressure to react, did little to restrain the use of fossil fuel. “More research” was the mantra everyone adopted, and funding for it flowed freely from governments and foundations. Under the auspices of the United Nations, scientists and governments set up a curious hybrid, the IPCC, to track and report on the progress of that research.
From roughly 1988 to 1995, the hypothesis that burning coal and gas and oil in large quantities was releasing carbon dioxide and other gases that would trap the sun’s radiation on earth and disastrously heat the planet remained just that: a hypothesis. Scientists used every means at their disposal to reconstruct the history of the earth’s climate and to track current changes. For example, they studied the concentration of greenhouse gases in ancient air trapped in glacial cores, sampled the atmosphere with weather balloons, examined the relative thickness of tree rings, and observed the frequency of volcanic eruptions. Most of all, they refined the supercomputer models of the earth’s atmosphere in an effort to predict the future of the world’s weather.
By 1995, the central Herculean tasks of both research and synthesis were largely complete. The report the IPCC issued that year was able to assert that “the balance of evidence suggests” that human activity was increasing the planet’s temperature and that it would be a serious problem. This was perhaps the most significant warning our species, as a whole, has yet been given. The report declared (in the pinched language of international science) that humans had grown so large in numbers and especially in appetite for energy that they were now damaging the most basic of the earth’s systems—the balance between incoming and outgoing solar energy. Although huge amounts of impressive scientific research have continued over the twelve years since then, their findings have essentially been complementary to the 1995 report—a constant strengthening of the simple basic truth that humans were burning too much fossil fuel.
The 1995 consensus was convincing enough for Europe and Japan: the report’s scientific findings were the basis for the Kyoto negotiations and the treaty they produced; those same findings also led most of the developed world to produce ambitious plans for reductions in carbon emissions. But the consensus didn’t extend to Washington, and hence everyone else’s efforts were deeply compromised by the American unwillingness to increase the price of energy. Our emissions continued to soar, and the plans of many of the Kyoto countries in Western Europe to reduce emissions sputtered. (At the same time, most tragically of all, China and India had just begun their rapid industrial takeoffs using precisely the technologies we then knew were wreaking havoc; they did not seek or find much aid from the Western countries that could have encouraged them to take a more benign path.) In 2001 the IPCC issued its Third Assessment Report (TAR), but it coincided with the start of the Bush administration, which refused even to consider a serious policy for climate. The IPCC’s new Fourth Assessment of this February (known as AR4) arrives at a more congenial moment, as the new Democratic Congress takes up a wide variety of legislation designed, finally, to curb emissions.
The finding of the new report that attracted the most attention in the press was that scientists were now more confident than ever that the warming we’ve seen so far (about one degree Fahrenheit in the average global temperature) was caused by human beings. Instead of being merely “likely,” the conclusion was now “very likely,” which in the IPCC’s lexicon means better than a 90 percent chance. But it’s been years since any reputable scientist specializing in climate research doubted that conclusion. More important findings were ignored in accounts of the report and in some cases were obscured by the document’s very poor prose, which is much more opaque than its predecessors. Those findings include:
- The amount of carbon in the atmosphere is now increasing at a faster rate even than before.
- Temperature increases would be considerably higher than they have been so far were it not for the blanket of soot and other pollution that is temporarily helping to cool the planet.
- Alternative explanations for some of the warming (for example, sunspot activity and the “urban heat island effect,” the raising of temperatures in cities caused by high building densities and the use of heat-retaining materials such as concrete and asphalt) are now known to be relatively negligible.
- Almost everything frozen on earth is melting. Heavy rainfalls are becoming more common since the air is warmer and therefore holds more water than cold air, and “cold days, cold nights and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent.”
These facts serve as the prelude to the most important part of the new document, its predictions for what is to come. Here too the news essentially confirms the previous report, and indeed most of the predictions about climate change dating back to the start of research: if we don’t take the most aggressive possible measures to curb fossil fuel emissions immediately, then we will see temperature increases of—at the best estimate—roughly five degrees Fahrenheit during this century. Technically speaking, that’s enormous, enough to produce what James Hansen has called a “totally different planet,” one much warmer than that known by any of our human ancestors.
The process by which the IPCC conducts its deliberations—scientists and national government representatives quibbling at enormous length over wording and interpretation—is Byzantine at best, and makes the group’s achievements all the more impressive. But it sacrifices up-to-the-minute assessment of data in favor of lowest-common-denominator conclusions that are essentially beyond argument. That’s a reasonable method, but one result is that the “shocking” conclusions of the new report in fact lag behind the most recent findings of climate science by several years.
That’s most obvious here in the discussion of the rise in sea level. Researchers know that sea levels will rise fairly quickly this century, in part because of the melting of mountain glaciers and in part because warm water takes up more space than cold. The new assessment refines the calculations of the rise in sea level and puts the best estimate at a foot or two, which is actually slightly less than the last assessment in 2001. Though it doesn’t sound like much, a couple of feet is actually a large amount—enough to inundate many low-lying areas and drown much of the earth’s coastal marshes and wetlands. Still, it might be more or less manageable.
During the last eighteen months, however, new research has indicated that a far more rapid rise in sea level may be possible, because the great ice sheets of Greenland and the Antarctic appear to have begun moving more quickly toward the sea. Some of this research appeared in Al Gore’s movie An Inconvenient Truth, and James Hansen has written in these pages about this new information*; it is responsible for much of the recent increase in the level of alarm. But it is not included in the IPCC report, except as a caveat: “larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.”
In short, the new report is a remarkably conservative document. That it is still frightening in its predictions simply indicates the huge magnitude of the changes we’re now causing, changes far larger than most people fully understand. Even using its conservative projections, the panel states unequivocally that typhoons and hurricanes will likely become more intense, that sea ice will shrink and perhaps disappear in the summertime Arctic, that snow cover will contract. Later this year, a second working group will outline the effects of these changes on humans, translating inches of sea-level rise into numbers of refugees, showing the effects of increases in temperature and humidity on malaria-carrying mosquitoes as well as the impact of heat waves on crop losses. The language will still be bloodless, but the findings obviously won’t.
The IPCC has always avoided taking political positions—it doesn’t recommend specific policies—and it continues this tradition with its new report. In its discussions of the momentum of climate change, however, it does introduce one particularly disturbing statistic. Because of the time lag between carbon emissions and their effect on air temperature, even if we halted the increase in coal, oil, and gas burning right now, temperatures would continue to rise about two tenths of a degree Celsius per decade. But, the report writes, “if all radiative forcing agents [i.e., greenhouse gases] are held constant at year 2000 levels, a further warming trend would occur in the next two decades at a rate of about 0.1å¼C per decade.”
Translated into English, this means, to put it simply, that if world leaders had heeded the early warnings of the first IPCC report, and by 2000 had done the very hard work to keep greenhouse gas emissions from growing any higher, the expected temperature increase would be half as much as is expected now. In the words of the experts at realclimate.org, where the most useful analyses of the new assessment can be found, climate change is a problem with a very high “procrastination penalty”: a penalty that just grows and grows with each passing year of inaction.
This is why the most important news about climate at the moment may come not from the IPCC but from Washington. After twenty years of inactivity—a remarkably successful bipartisan effort to accomplish nothing—the first few weeks of the new Congress have witnessed a flurry of activity. A series of bills have been introduced by people ranging from California Representative Henry Waxman and Vermont Senator Bernie Sanders to Arizona’s John McCain that would call for more or less aggressive carbon reduction targets. Some of the bills would set in place a “cap-and-trade” system that would set overall limits on emissions of carbon dioxide but would allow companies to freely buy and sell credits permitting them to emit certain amounts of it; this would produce a market for carbon-cutting measures.
The IPCC report doesn’t call for particular reduction figures. It does, however, make clear that reduction in emissions must be quick and deep. There is no more optimistic alternative. Even if we do everything right, we’re still going to see serious increases in temperature, and all of the physical changes (to one extent or another) predicted in the report. However, there’s reason to hope that if the US acts extremely aggressively and quickly we might be able to avoid an increase of two degrees Celsius, the rough threshold at which runaway polar melting might be stopped. This means that any useful legislation will have to feature both a very rapid start to reductions and a long and uncompromising mandate to continue them. Sanders’s bill, also endorsed by California’s Barbara Boxer, who heads the relevant committee, comes closest to that standard. It calls for an eventual 80 percent cut in emissions by 2050. McCain’s bill, cosponsored by one of his challengers for the presidency, Barack Obama, is somewhat weaker in its eventual targets. But the bargaining has barely begun, and in any event quick initial implementation of any cuts will be almost as important as the final numbers.
No one expects President Bush to sign such a bill. In fact, it was widely considered a minor miracle that he uttered the words “climate change” in this year’s State of the Union address. (His limp proposal, centering on alternative fuels for some vehicles, was equally widely considered a dud.) What’s happening now has much to do with positioning for the next presidential election, and the legislation that will eventually be passed and signed in 2009. What the IPCC report makes clear by implication is that that legislation will be our last meaningful chance: anything less than an all-out assault on carbon in our economy will be rendered meaningless by the increasing momentum of global warming. And of course by now our economy is only part of the problem. Though we use more energy per capita than any other country, the Chinese may pass us in total carbon emissions by decade’s end. Even if we start to get our own house in order, we’ll need to figure out how, with desperate speed, to lead an equally sweeping international response.
The only really encouraging development is the groundswell of public concern that has built over the last year, beginning with the reaction to Hurricane Katrina and Al Gore’s movie. In January, a few of us launched an initiative called stepitup07 .org. It calls for Americans to organize rallies in their own communities on April 14 asking for congressional action. In the first few weeks the Web site was open, more than six hundred groups in forty-six states registered to hold demonstrations—this will clearly be the largest organized response to global warming yet in this country. The groups range from environmental outfits to evangelical churches to college sororities, united only by the visceral sense (fueled in part by this winter’s bizarre weather) that the planet has been knocked out of whack. The IPCC assessment offers a modest account of just how far out of whack it is—and just how hard we’re going to have to work to have even a chance at limiting the damage.
Corrections May 10, 2007