atmosphere measured by weather balloons, and temperature of the lower atmosphere measured by orbiting satellites—all show no warming (see Figure 1). The observed warming since the late 19th century is 0.6°C, or one-third of the predicted value. Critics argued, as I did before the House, that there would have to be a dramatic reduction in the prediction of future warming in order to reconcile fact and forecast. By 1995, in its second full assessment of climate change, the IPCC admitted the validity of its critics' position: "When increases in greenhouse gases only are taken into account...most [climate models] produce a greater mean warming than has been observed to date, unless a lower climate sensitivity [to the greenhouse effect] is used...There is growing evidence that increases in sulfate aerosols are partially counteracting the [warming] due to increases in greenhouse gases." (2) IPCC is presenting two alternative hypotheses: Either the base warming was simply overestimated, or, some other anthropogenerated emission is preventing the warming from being observed. Which is more likely to be true? Are sulfate aerosols responsible for the now-admitted dearth of warming? Several attempts have been made to demonstrate this; the most prominent appeared in Nature on July 4, 1996 (3), and appeared to bolster the argument that the sulfates were masking the expected warming. This particular paper received widespread publicity as it was published a mere week before an important United Nations meeting on climate change in Geneva. At that meeting, Under Secretary of State Timothy Wirth stated that "the science is convincing" on global warming, largely in response to this work. That particular study used annual weather balloon data from 1963 through 1987. Most striking was a rapid warming of the middle of the Southern Hemisphere, where there in fact are virtually no sulfates available to counter greenhouse warming. However, when the entire record of weather balloon data, from 1958 through 1995, was used, this most pronounced region of warming turned out to show no change whatsoever (4) (Figure 2). In response to this, the senior author of the original study told the December meeting of the American Geophysical Union that the correspondence between the sulfate-greenhouse model and reality vanished because greenhouse warming in the Northern Hemisphere had overwhelmed sulfate cooling since 1987. This was reiterated in the July 16, 1997 issue of New Scientist (5). As there was no net change in any of the temperature records in the last decade (Figure 1), this statement was clearly wrong. The default option—that it's simply not going to warm as much as the earlier projections had indicated—is increasingly attractive. And a new suite of climate models, which now seem to fit the observed history more accurately, bear witness to this conclusion. Figure 3 shows temperature changes projected by the new model from the U.S. National Center for Atmospheric Research (NCAR), as published in the May 16 issue of Science (6). We have performed a linear adjustment to allow for the fact that effective greenhouse emissions have historically increased (over the last several decades) at the exponential increase rate of 0.7%/year globally, a figure that is highly consistent with median IPCC estimates. The NCAR model assumed a 1.0%/year increase. Figure 3. Temperatures predicted by the new NCAR model estimated using the more realistic increase, as given by the IPCC 1995, of 0.7 percent per year. The Nature of Observed Change Greenhouse physics predicts that the driest airmasses should respond first and most strongly to changes induced by human activities. These, in fact, are generally the coldest airmasses, such as the great high pressure system that dominates Siberia in the winter, and its only slightly more benign cousin in northwestern North America. When the jet stream attains a proper orientation, it is this airmass that migrates south and kills orange trees in Florida. A look at the trends in the satellite data—our only truly global record of lower atmosphere temperature—is remarkably revealing. There is a statistically significant global cooling trend (Figure 4) over the 18.8 year period of record. A latitudinal breakdown of the satellite data is very revealing. As shown in Figure 5, there is a sharp warming of the midlatitude land areas of the Northern Hemisphere. These are largely the regions that should show sulfate cooling! On the other hand, almost every latitude band in the Southern Hemisphere, where greenhouse warming should operate unfettered, either shows no change or is cooling! The reliability of the satellite data is quite apparent when its annual readings are compared to those from weather balloons between 5,000 and 30,000 feet. This is well known and shown in Figure 6. But perhaps more interesting is a comparison of winter minus summer temperature changes over the period of concurrence between the satellite and the ground-based thermometers, which is 1979 to the present; these are shown in Figure 7. The correspondence is nearly as remarkable as is the agreement between the satellites and the weather balloons. Another way to appreciate observed change in a frame of reference longer than the satellite record is to look at the ground-based thermometers for the last fifty years. In Figure 8, I have subtracted the summer temperature changes from the winter ones, as in Figure 7. The redder the map, the more pronounced is the warming in the winter versus the summer. All of these observations argue that the first alternative proposed in 1995 by the IPCC-that the climate is less sensitive to greenhouse changes than previously thought—is much more likely than the facile explanation that sulfate aerosol somehow cancelled the warming. Temperature Departure (°C) .6 Satellite-measured Temperatures Figure 6. Temperature measured by satellites (closed circles) match up nearly perfectly with temperatures measured from weather balloons in the layer between 5,000ft and 30,000 ft. (open circles). 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 The Administration's Program: How Much Warming is Prevented? As noted above, the most likely explanation for the now-acknowledged warming deficit is that the sensitivity of global temperature to greenhouse effect changes was overestimated. There are several reasons why this may have been the case, but perhaps the most compelling is that all of the general circulation climate models that have (to date) been referenced by IPCC contain substantial "flux adjustments" for the poleward transport of heat. In plain language, these models have to be "adjusted" arbitrarily in order to keep them from producing unrealistic climates. Generally (but not always) an additional increment of heat moving northward is required. The obvious implication is that, left alone, the polar regions would |