The National Academies' National Research Council (NRC) has belly-flopped into the stormy politics of global warming. At the request of the White House, an NRC committee conducted a review of climate change science that alarmists seized as proof of the need for urgent response. In fact, the study report is a serviceable if spotty summary of what's known and-more importantly-what's not known about the climate.
Where the effort stumbles is in the report summary's already-famous first sentences: "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising."
On the basis of those unqualified assertions, the NRC study is now cited in popular discourse as proof of the need for radical warming precautions. Yet it is no such thing.
'Considerable uncertainty'
Qualification eases into view in the summary's largely ignored third sentence: "The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes are also a reflection of natural variability."
Fraying at that point, certitude unravels altogether in the next paragraph: "Because there is considerable uncertainty in current understanding of how the climate system varies naturally and reacts to emissions of greenhouse gases and aerosols, current estimates of the magnitude of future warming should be regarded as tentative and subject to future adjustments (either upward or downward)."
The rest of the report elaborates that uncertainty. So what led the authors, all lavishly credentialed scientists, to so misleadingly imply certainty where none exists? Didn't they know that the mass media would gravitate to simplicity and drama and ignore the rest of their work?
What a mess for US President George W. Bush. The NRC released a "prepublication copy" of the report just before he traveled to Europe, where politics long ago drubbed global-warming science into quiet submission. Bush's sensible refusal late in March to sacrifice American prosperity to the Kyoto Protocol on Climate Change appalled European governments, none of which has itself ratified the agreement. The sense was palpable last week that the US president was in for a heavy dose of environmentalist condescension.
Bush and his speechwriters did their best to preempt the scolding. In a statement on global warming, Bush focused on the NRC report's attention to uncertainty.
Noting measured increases in average surface temperatures, the president said, "...The academy's report tells us that we do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could or will change in the future. We do not know how fast change will occur or even how some of our actions could impact it." Of course, Bush's tutelage wasn't likely to distract European politicians from the NRC report's first two sentences.
Except for its discordant start, the NRC review deals even-handedly with complex scientific questions that have fused into a fierce political issue. But it does suffer from omission.
There is no mention, for example, of a recent report that estimates of surface temperatures for the past 20 years are overstated by 40% because of problems with sea samples. If substantiated, the error would pull apparent warming easily into the range of natural variability. It also would annul a pivotal NRC assumption. The size of recently observed warming in comparison with natural change simulated by climate models makes the NRC scientists suspect "linkage" between the buildup of greenhouse gases in the atmosphere and the rise in temperature. Downward correction of the surface-temperature rise would weaken the linkage argument. It also would invalidate the summary's first sentence.
Other causes
Furthermore, weakening of the gas-temperature link would increase the relative importance of other warming causes, such as solar activity. NRC gives the sun one-third the weight of carbon dioxide as a warming influence. Some scientists argue for heavier weighting because surface temperature changes correlate better with solar variation than they do with greenhouse-gas concentrations.
By reinvigorating debate over subtle points like those, the NRC report might have advanced knowledge about climate science. By mishandling its message, it instead fed a political panic more likely than global warming to damage human welfare.
