The latest installment of the ongoing melodrama about global warming occurred last week with the release of the Clinton administration's "U.S. National Assessment of the Potential Consequences of Climate Variability and Change for the Nation."
To be sure, there will be some upsides to warming (primarily greater agricultural yields), but for the most part the report predicts doom and gloom for the coming century.
While the press is eating this stuff up ("End is near" makes a pretty good headline), the public is showing remarkably good judgment by heavily discounting these prophesies of apocalypse.
Let us start by considering how hard it is to forecast the weather, even for the upcoming weekend. Then consider the hit-and-miss nature of predictions about what kind of summer or winter might be in store for us in any given year. Then ponder the difficulties of predicting weather patterns 100 years out. It boggles the mind, particularly when we reflect on all the industrial and technological changes that will heavily influence the extent of greenhouse gas emissions and our ability to mitigate them. The assessment, to its credit, frankly acknowledges the uncertainties, but they are noted in passing and not allowed to intrude on the parade of horribles that march through the report.
Surprisingly, the report begins by postulating a 5-to-10 degree Fahrenheit warming over this century, a range far higher than that predicted by the computer models used in the report (which predicted warming between 3.6 and 6.3 degrees Fahrenheit). Moreover, there are two fundamental problems with the assumptions relied on by the computers.
First, the report's computer modelers postulated a 1 percent increase in greenhouse gas emissions each year, a figure 2.5 greater than the observed 0.4 percent annual increase in emissions over the past two decades. Even the somewhat-alarmist International Panel on Climate Change (IPCC) predicts only an annual 0.63 percent emissions increase over this century. That simple error alone reduces the warming predicted in the assessment by one-third to one-half.
Second, the models assume that warming will dramatically accelerate in the future because air pollution from sulfate aerosols, which is thought to artificially cool the planet, will decrease. Yet the "sulfate-masking" hypothesis has been torn to shreds by scientists in the peer-reviewed literature, and even NASA's James Hansen, perhaps the world's foremost expert on climate change, no longer believes that pollution is temporarily protecting us from the full brunt of global warming.
The report generates most of its disaster scenarios by assuming a relatively even distribution of this dramatic warming, but the data clearly show that warming has thus far been fairly modest and almost entirely concentrated in the far northern latitudes, at night and during the winter. There is good reason for this: Cold, dry air masses warm faster and to a greater extent than moist air for any given increment of greenhouse gas emissions.
Moreover, warming moist air increases cloud cover, which reduces temperatures during the day but increases them at night. Most climatologists believe that warming nighttime winter temperatures in the north would result in benign or largely positive changes in climate.
Finally, there is the report's dubious prediction that warmer weather will cause more extreme weather events. Even the IPCC notes there is no evidence extreme weather events are more likely now than they were in the past, despite the century-long buildup of greenhouse gases. In fact, the number of storms and other extreme weather events, along with their severity, are trending down, not up. One can find just as many peer-reviewed articles arguing those downward trends will continue as articles arguing the opposite.
It should surprise no one the "national assessment" has political fingerprints all over it. A senior scientist involved in the project told the New York Times that the report's conclusions are still subject to revision but that the administration was determined to release the summary now to affect the November elections. The summary itself plays up the degree of "stakeholder involvement" in the development of the report, a clear signal that politically active interest groups had a hand in the document.
And not surprisingly, the press releases accentuate the negative, even though the report concludes that, despite these worst-case assumptions about warming trends, society will likely have little trouble adjusting to climate-induced changes.
The assessment, in sum, sheds more heat than light on the future impact of climate change. But in an election year, what else should we really expect?