Morning Review: The Bushites and Climate Change

A number of press outlets have devoted space to a recent Bush Administration report on global climate change, in which government climate researchers acknowledge that humans do contribute to global warming. Although there's much of interest in the report -- Our Changing Planet, from the U.S. Global Change Research Program -- most of the news coverage pivots on a brief paragraph in the report's "Climate Variablity and Change" chapter that, in essence, says you can't understand the North American climate pattern of the past half-century or so without assuming at least some human influence. I'll quote the paragraph the press found most eye-catching in full here:

A recent study shows that the average global results reported above also pertain over the North American region. Several indices of large-scale patterns of surface temperature variation were used to investigate climate change in North America over the 20 th century. The observed variability of these indices was simulated well by several climate models. Comparison of index trends in observations and model simulations shows that North American temperature changes from 1950 to 1999 were unlikely to be due only to natural climate variations. Observed trends over this period are consistent with simulations that include anthropogenic forcing from increasing atmospheric greenhouse gases and sulfate aerosols. However, most of the observed warming from 1900 to 1949 was likely due to natural climate variation.

News sources tended to report this as an abrupt volte-face by the administration. The reality, I think, is a bit more subtle. Note, for example, that the paragraph doesn't really say just how much of an impact anthropogenic forcings have had relative to natural ones -- only that the numbers for North America don't come out right unless you include some kind of anthropogenic effect. In this, the paragraph above echoes language slightly earlier in the report referring to global (rather than solely North American) temperatures, where it says that multiple numerical simulations "show that observed globally averaged surface air temperatures can be replicated only when both anthropogenic forcings, e.g., greenhouse gases, as well as natural forcings such as solar variability and volcanic eruptions are included in the model."

Cynic that I am, I find myself picturing the many late-night sessions of language-shading and parsing among government scientists, political appointees, and flacks that must have gone on before everyone agreed to this ambiguous language. Curiously, though, a remarkable diagram that appears in the same section of the report undermines the effect of this carefully hedged language:



What's being shown here are historical global temperature trends. The blue field shows temperatures that would be expected if natural forcing (such as solar variablity and the effect of aerosols from volcanic eruptions) alone are included in the calculation; the pink field shows the expected trend if you factor in both natural forcings and anthropogenic greenhouse gases; the black line shows the actual trend of temperature anomalies (the difference, in degrees C, between temperatures in the year in question and the 1890-1919 mean). Note the nice fit of the black line with the model that includes anthropogenic forcing -- and note that natural forcings, considered alone, provide only fluctuations about the mean, with no upward trend. Translation: Anthropogenic forcing is not only a part of the global warming story; it's the main part of the story.

You won't find a statement this bald anywhere in the report (at least as far as I can tell from a cursory examination). Still, it does acknowledge some human influence on climate, and I suppose that's something. And elsewhere, the report acknowledges that global warming (whatever its causes) is already having effects on sea level, crop yields, weather patterns, etc., etc.

So this just in: Global warming is happening, and humans are at least partly to blame.

But is this carefully hedged position really such a departure from what our mendacious current admministration has declared in the past? Three years ago, when the National Academy of Sciences released its own report on the probable role of humans in global warming, Bush's response seems to have been essentially, "Yes, humans have some role in warming, but we need to know more before we can do anything about it." The recent report, while moving the administration further in the direction of admitting what the NAS and IPCC have already established, still seems, in its actual language, to be very much in that tradition, marking out a position of sufficient ambiguity to allow for inaction while maintaining the appearance of action, open-mindedness, and moderation. (Just right for RNC season.)

In any event, it looks like it would be vain to hope that this new apparent acknowledgment of some human role in warming will translate into a decent climate change policy, or even cursory movement toward one. Bush's science adviser was quick to stress that the report has "no implications for policy," and argued that "there is no discordance between this report and the president's position on climate." Bush himself seems to agree; when asked why the Administration had changed its position on human-induced warming, he responded, in his most Presidential Fashion, "Ah, did we? . . . I don't think so." How's that for decisive leadership?

Conclusion: More pre-convention eyewash.