Thank you for soliciting my testimony on climate change. Specifically, I have been asked to comment on the climatic effects of current proposals for greenhouse gas emission reduction. I will examine the currently debated position, a proposed reduction of emissions to 1990 levels sometime during the period 2008 to 2012. However, before such examination can be made, it is necessary to decide on what model or scenario best describes the future climate.
The First Scientific Assessment of the United Nations Intergovernmental Panel on Climate Change (IPCC, 1990), stated that “when the latest atmospheric models are run with the present concentrations of greenhouse gases, their simulation of climate is generally realistic on large scales.”1 The suite of climate models extant at the time predicted that the globe’s mean temperature should have risen by 1.3oC to 2.3oC, with the larger figure for the Northern Hemisphere, where most of us live. These models provided the technical background for the Framework Convention on Climate Change, signed in 1992.
Nearly ten years ago, I first testified on climate change in the U.S. House of Representatives. At that time, I argued that forecasts of dramatic and deleterious global warming were likely to be in error because of the very modest climate changes that had been observed to that date. Further, it would eventually be recognized that this more moderate climate change would be inordinately directed into the winter and night, rather than the summer, and that this could be benign or even beneficial. I testified that the likely warming, based on the observed data, was between 1.0oC and 1.5oC for doubling the natural carbon dioxide greenhouse effect.
Since that first testimony, the global mean temperature of the earth has not warmed a bit. Three independent measuring systems - surface measured temperature, temperature of the lower atmosphere measured by weather balloons, and temperature of the lower atmosphere measured by orbiting satellites - all show no warming.
Figure 1. Global Temperature Departures
|Figure 1. During the last 10 years (1987-1996) neither the surface thermometers, weather balloons, nor satellites observe any net warming in annual tempature departures.|
The observed warming since the late 19th century is 0.6oC, 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, 19963, 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 whatsoever4 (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 Scientist5. As there was no net change in any of the temperature records in the past decade (figure 1), this statement was clearly wrong.
Figure 2. Temperature Trend from 1963 - 1987 (degrees C)
|Figure 2. Observed warming in Santer et al. (1996) from 1963 to 1987 (top). The highlighted region in the Southern Hemisphere shows the strong observed warming. The entire temperature history over the same region from 1957 to 1995 shows no significant warming trend (bottom). However, the period that was chosen for study by Santer et al. (filled circles) warms dramatically.|
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. 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. Global Temperature Change (from NCAR, 1997)
|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 air masses 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.
Figure 4. Global Satellite-Measured Temperature Departures
|Figure 4. Monthly average global temperature departures as measured by satellites shows a statistically significant decline since the measurements began in 1979. This has occurred during a period when GCMs indicate that the earth should have warmed 0.6 C according to greenhouse models, and 0.35 C according to sulfate-greenhouse models.|
A latitudinal breakdown of the satellite data is very revealing. 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!
|Figure 5. Satellite temperature trends (degrees C/decade) by latitude bands. Note that there is cooling or no change everywhere except the mid-latitude land areas of the Northern Hemisphere.|
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. 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. 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.
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.
|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 30,000ft. (open circles).|
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 become too cold and the tropics too warm.
A very few of the most recent models do not contain this type of adjustment, including the one detailed in Figure 3. Not suprisingly, it predicts considerably less warming than its adjusted counterparts.
Table 1 gives the equivalent carbon dioxide concentration of the atmosphere, in parts per million (ppm), given a continuation of the current exponential increase in emissions, and under the program proposed by the Administration. Under the Administration’s plan, we assume that emissions reductions begin around 2004 and that they reach 1990 levels by 2010 and remain constant after that. We assume that the entire world does the same. We also assume that the time-behavior of the NCAR model is roughly linear through these increments of greenhouse gas. This is a characteristic common to almost all climate models.
Projected Effective CO2 Increase
Table 1. The effect that the Clinton “plan” will have on atmospheric carbon dioxide levels and the resulting temperature savings (based on NCAR model results and the IPCC “best guess” emission scenario.)
Figure 9 compares the NCAR results for the next 50 years with and without the Administration program. The amount of “saved” warming is infinitesimal: 0.13oC. It is doubtful that this change could even be extracted from ground based temperature measurements, owing to problems with increasing urbanization and land-use alterations. However, it should be apparent in satellite measurements, which are accurate to within plus or minus 0.01oC.
|Figure 9. Warming in the NCAR model with (dotted line) and without (solid line) the proposed Administration program for the next 50 years. The total “saved” warming is 0.13 degrees C, assuming emissions return to 1990 levels by 2010 and then stay constant, and that the entire world does the same.|
What Should be Done?
Emissions trading proposed by the Administration is simply a “hidden” tax that ultimately falls on the consumer and discourages spending. Each consumer is impoverished a small amount while emissions are forcibly reduced.
Is this what we really want? I think not. Rather, it might be wiser to allow people to keep their money. Many will invest their funds in technologies that will produce substantial energy at reduced cost. Some of these will produce few if any greenhouse emissions.
The lessons of technological history are clear. Each century brings about changes that are simply unanticipated but revolutionary. 100 years ago, senior scientists and public officials worried that America would be deforested by the 1920s and that disease would be rampant in urban areas because of the alarming increase in horse traffic. Amidst all this concern, the automobile and the fossil fuel-powered economy were soon to appear. Its development was driven less by concern for the environment than it was by the profit motive. Those who saw this opportunity did well. If there was a substantial horse tax, there would have been less to invest.
A similar argument could be made for nearly 200 years ago. In the early years of the 19th century, the U.S. government fretted over nascent Manifest Destiny. If it had gathered a team of “top scientists” to recommend how to move goods and people across this vast nation, they would doubtless recommended a substantial and very expensive network of barge canals. Fortunately, there was no massive tax levied to make this happen. But if there were, it would have taken place just as the steam engine and fixed rail transit were being invented.
As we debate this issue and what to do, there are probably 10,000 people tinkering and thinking about fuel cells, hydrogen power, and undreamed-of exotica that will displace our current energy system. Let’s save our citizens’ money. Let’s allow them to invest in the future, take the risks and reap the rewards. Better to do that than tax them to solve a problem that is not all that emergent, and one that will nonetheless resolve itself faster if only we would get out of the way.
1. Houghton, J.T., G.J. Jenkins, and J.J. Ephraums (Eds.)(1990). Climate Change: The IPCC Scientific Assessment. Cambridge University Pres.
2. Houghton, J.T., L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell (Eds.)(1996). Climate Change 1995: The Science of Climate Change. Cambridge: Cambridge University Press.
3. Santer, B. D. et al. (1996). A Search for Human Influences on the Thermal Structure of the Atmosphere. Nature, 382, 39-45.
4. Michaels, P.J. and P.C. Knappenberger, 1996. Human Effect on Global Climate? Nature, 384, 522-523.
5. Pearce, F., 1997. Greenhouse Wars. New Scientist, 139, 38-43.
6. Kerr, R.A. (1997). Model Gets It Right - Without Fudge Factors, Science, 276, 1041
Statement of financial support from the U.S. government:
1996-1999 U.S. Department of Commerce. Cold Air Volume and Persistence in the Mid-Atlantic Region. $90,000.
1996-1998. U.S. Department of Energy. Greenhouse Influences on Diurnal Warming and Cooling Rates. $100,000.