I was an official reviewer of the overall report. Because various versions of the document have leaked onto the Internet in recent months, I’ll take the liberty of using it as a good reference guide for the new summary.
Want my candid opinion about the summary? Ho-hum. Despite breathless news reports, there’s very little in it that’s new to anyone involved in global warming science. Instead, there have been dozens of stories about how scientists now believe there is a definite human influence on mean global surface temperature, and that, in recent decades, much of the warming can be attributed to the effect of increasing amounts of carbon dioxide and methane in the atmosphere.
Scientifically, this is tantamount to concluding that because Las Vegas is awash in poker chips and prophylactics, we now have high confidence that much of the recent decades’ increase in economic growth has something to do with the prevalence of gambling and hanky-panky.
In the case of the atmosphere, the evidence is even more suggestive. For longer than any active climate scientist has been alive, it has been known that increasing atmospheric carbon dioxide should result in a preferential warming of winter (versus summer) temperatures, a warming of the coldest nights of the winter more than the hottest days of summer, and a general cooling of the global stratosphere.
All three have been observed for well over a decade. So much for the big “news” in the summary.
Nor should this surprise: The biggest story in the summary was largely missed by the environmental media. The IPCC now projects, in its mid-range scenario for carbon dioxide emissions, that the maximum rise in global sea level in this century will be around 17 inches. That’s a reduction of 30 percent from what was in the Third Scientific Assessment, published just six years ago.
That’s huge news, or it should be. But instead of listening to what the IPCC is saying, people are opting for the science fiction of Al Gore’s “An Inconvenient Truth,” whose central disaster scenario is that Greenland sheds the majority of its ice this century, raising sea level as much as 20 feet. Much of Florida disappears, and the Mall in Washington goes under water. The U.N.’s sea-level projections “include a contribution due to increased ice flow from Greenland and Antarctica, but these flow rates could increase or decrease in the future.”
That’s excellent hedging by the IPCC, because the authors of the summary surely knew that a paper was about to appear in the journal Science showing that an increase in the loss of ice from Greenland’s big glaciers in 2004 had stopped and reversed by 2006. And was the loss of ice ever as gargantuan as Gore’s imagery? Hardly. Satellite data, also published in Science last October, show that Greenland was losing a total of only 25 cubic miles of ice per year. That’s teeny. There are 630,000 cubic miles of ice up there. Dividing 25 into 630,000 and multiplying by 100 gives the rate of loss: 0.4 percent of Greenland’s ice per century.
It’s unfortunate that the summary didn’t take Gore’s Greenland science fiction head-on. It would have been as simple as highlighting the temperature history of southern Greenland - the region of greatest ice loss - in the U.N.’s own climate history. As is obvious, temperatures in the most recent decade aren’t at all warm compared with the 50 years between 1915 and 1965. If Greenland didn’t raise sea level appreciably then (and it didn’t), why will it suddenly do so now?
Instead, climate models in the upcoming report take an awfully long time to shed the majority of Greenland’s ice: After 1,130 years, 60 percent disappears if we maintain the concentration of atmospheric carbon dioxide at four times above the level it was around 1900.
Right now, we’re only about 1.3 times that value, and there’s a reasonable debate about whether we will ever get to twice that figure, because in the time frame required, technology is likely to change dramatically, in ways we can’t imagine today.
For an interesting thought experiment, consider the energy and technology world of 1900, and a vision of the future. “Scientists will discover a new element called plutonium,” some placard-carrying crackpot on the horse-infested streets of New York might say, “and if we compress a few pounds of it, almost all the buildings on Manhattan will be destroyed, along with their inhabitants.” What a wacko! And that’s nothing, compared with his assertion that, by 1975, people would fly from New York to London in a little over three hours, 65,000 feet in the air, or that all of the information in all the libraries of the Earth could be on everyone’s desktop by 2000.
But that’s how technology changes in a century. There were similar changes between 1800 (horse power and hand-carried letters) and 1900 (iron-horse power and the telegraph, etc.), so it’s a real stretch to say we will go all the way to four times the 1900 concentration of carbon dioxide and then stay there for over a millennium. Does anyone seriously believe we will be a fossil fuel-powered society, industrially respiring massive amounts of carbon dioxide, in the year 2500?
Even the reduced estimates of maximum sea-level rise in the new IPCC report are likely to be high. That’s because all of their scenarios for the future include an increase in atmospheric methane, a potent global warming gas, at least through 2050, and most increase it even beyond then.
Methane increases in the atmosphere began to slow some 20 years ago, and in recent years the concentration has actually gone down. Nobel laureate Sherwood Rowland, who first hypothesized that chlorofluorocarbon refrigerants and propellants could reduce stratospheric ozone, recently predicted that the IPCC’s methane emissions scenarios are “quite unlikely.”
While it’s hard to disagree with the IPCC’s broad conclusions about human-induced warming and sea-level rise, there are several instances where the summary misses some obvious and important findings. For example, it asserts that “mountain glaciers and snow cover have declined on average in both hemispheres.” While that is generally (but not specifically) true for glaciers, data from the Global Snow Laboratory at Rutgers University show that total Northern Hemisphere snow cover has been unchanged for the last 20 years.
One problem with “consensus” documents such as the Fourth Assessment is that they take a long time to produce, and there is a deadline beyond which new scientific findings are excluded. Consequently, a very important part of the summary talks about how the top 10,000 feet of “the ocean has been absorbing more than 80 percent of the heat added to the climate system.”
Last summer, after the drop date, J.M. Lyman of the National Oceanic and Atmospheric Administration demonstrated a remarkable change between 2003 and 2005, which “represents a substantial loss of heat over a two-year period, amounting to about one-fifth of the long-term upper-ocean heat gain between 1955 and 2003.” In other words, in two years, somehow the vast expanse of the upper ocean suddenly lost the equivalent of a decade’s worth of warming!
Further, most of the ocean’s warming is centered in a band in the middle of the Southern Hemisphere. As the esteemed Roger Pielke Sr., of the University of Colorado has recently written, “The actual global ocean warming reported in the IPCC (summary) over the last several decades occurred in just a relatively limited portion of the oceans.” This is certainly not indicated in the climate models that serve as much of the basis for the upcoming Fourth Assessment.
Then there’s the summary’s mysterious association of increasing westerly winds in the mid-latitude regions of both hemispheres with greenhouse warming. Meteorology students learn early on that the strength of these winds is related to the temperature contrast between the poles and the tropics. All global warming models predict that this contrast becomes less, which would decrease the power of these winds.
Finally, sometimes the economy of words required in a summary may preclude necessary perspective. The summary talks about how cold days have become less frequent, and hot days more so. In reality, greenhouse warming must warm the coldest days of winter more than the hottest ones in summer, a reality that is obvious from an inspection of U.S. temperature records over the last several decades. And after having been chilled to the bone for months, some people might rightfully ask, “What’s so bad about this?”
So let’s give the IPCC somewhere around two cheers. That’s probably about the best that can be expected when 18 pages, written by a committee of 33 contentious scientists, are supposed to summarize about 1,000 succeeding pages, which themselves were not availed to the most recent science.