Thank you for soliciting my testimony on climate change.Specifically, I have been asked to comment on the climatic effectsof current proposals for greenhouse gas emission reduction. I willexamine the currently debated position, a proposed reduction ofemissions to 1990 levels sometime during the period 2008 to 2012.However, before such examination can be made, it is necessary todecide on what model or scenario best describes the futureclimate.
The First Scientific Assessment of the United NationsIntergovernmental Panel on Climate Change (IPCC, 1990), stated that"when the latest atmospheric models are run with the presentconcentrations of greenhouse gases, their simulation of climate isgenerally realistic on large scales."1 The suite ofclimate models extant at the time predicted that the globe's meantemperature should have risen by 1.3oC to2.3oC, with the larger figure for the NorthernHemisphere, where most of us live. These models provided thetechnical background for the Framework Convention on ClimateChange, signed in 1992.
Nearly ten years ago, I first testified on climate change in theU.S. House of Representatives. At that time, I argued thatforecasts of dramatic and deleterious global warming were likely tobe in error because of the very modest climate changes that hadbeen observed to that date. Further, it would eventually berecognized that this more moderate climate change would beinordinately directed into the winter and night, rather than thesummer, and that this could be benign or even beneficial. Itestified that the likely warming, based on the observed data, wasbetween 1.0oC and 1.5oC for doubling thenatural carbon dioxide greenhouse effect.
Since that first testimony, the global mean temperature of theearth has not warmed a bit. Three independent measuring systems -surface measured temperature, temperature of the lower atmospheremeasured by weather balloons, and temperature of the loweratmosphere measured by orbiting satellites - all show nowarming.
Figure 1. Global Temperature Departures
|Figure 1. During the last 10 years(1987-1996) neither the surface thermometers, weather balloons, norsatellites observe any net warming in annual tempaturedepartures.|
The observed warming since the late 19th century is0.6oC, or one-third of the predicted value. Criticsargued, as I did before the House, that there would have to be adramatic reduction in the prediction of future warming in order toreconcile fact and forecast.
By 1995, in its second full assessment of climate change, theIPCC admitted the validity of its critics' position: "Whenincreases in greenhouse gases only are taken into account . . .most [climate models] produce a greater mean warming than has beenobserved to date, unless a lower climate sensitivity [to thegreenhouse effect] is used . . . There is growing evidence thatincreases in sulfate aerosols are partially counteracting the[warming] due to increases in greenhouse gases."2
IPCC is presenting two alternative hypotheses: Either the basewarming was simply overestimated, or, some other anthropogeneratedemission is preventing the warming from being observed. Which ismore likely to be true?
Are sulfate aerosols responsible for the now-admitted dearth ofwarming? Several attempts have been made to demonstrate this; themost prominent appeared in Nature on July 4,19963, and appeared to bolster the argument that thesulfates were masking the expected warming. This particular paperreceived widespread publicity as it was published a mere weekbefore an important United Nations meeting on climate change inGeneva. At that meeting, Under Secretary of State Timothy Wirthstated that "the science is convincing" on global warming, largelyin response to this work.
That particular study used annual weather balloon data from 1963through 1987. Most striking was a rapid warming of the middle ofthe Southern Hemisphere, where there in fact are virtually nosulfates available to counter greenhouse warming.
However, when the entire record of weather balloon data, from1958 through 1995, was used, this most pronounced region of warmingturned out to show no change whatsoever4 (figure 2). Inresponse to this, the senior author of the original study told theDecember meeting of the American Geophysical Union that thecorrespondence between the sulfate-greenhouse model and realityvanished because greenhouse warming in the Northern Hemisphere hadoverwhelmed sulfate cooling since 1987. This was reiterated in theJuly 16, 1997 issue of New Scientist5. As there was nonet 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 (degreesC)
|Figure 2. Observed warming in Santer etal. (1996) from 1963 to 1987 (top). The highlighted region in theSouthern Hemisphere shows the strong observed warming. The entiretemperature history over the same region from 1957 to 1995 shows nosignificant warming trend (bottom). However, the period that waschosen for study by Santer et al. (filled circles) warmsdramatically.|
The default option - that it's simply not going to warm as muchas the earlier projections had indicated - is increasinglyattractive. And a new suite of climate models, which now seem tofit the observed history more accurately, bear witness to thisconclusion.
Figure 3 shows temperature changes projected by the new modelfrom the U.S. National Center for Atmospheric Research (NCAR), aspublished in the May 16 issue of Science. We have performed alinear adjustment to allow for the fact that effective greenhouseemissions have historically increased (over the last severaldecades) at the exponential increase rate of 0.7%/year globally, afigure that is highly consistent with median IPCC estimates. TheNCAR model assumed a 1.0%/year increase.
Figure 3. Global Temperature Change (from NCAR,1997)
|Figure 3. Temperatures predicted by thenew NCAR model estimated using the more realistic increase, asgiven by the IPCC 1995, of 0.7 percent per year.|
The Nature of Observed Change
Greenhouse physics predicts that the driest air masses shouldrespond first and most strongly to changes induced by humanactivities. These, in fact, are generally the coldest airmasses,such as the great high pressure system that dominates Siberia inthe winter, and its only slightly more benign cousin innorthwestern North America. When the jet stream attains a properorientation, it is this airmass that migrates south and killsorange trees in Florida.
A look at the trends in the satellite data - our only trulyglobal record of lower atmosphere temperature - is remarkablyrevealing. There is a statistically significant globalcooling trend (figure 4) over the 18.8 year period ofrecord.
Figure 4. Global Satellite-Measured TemperatureDepartures
|Figure 4. Monthly average globaltemperature departures as measured by satellites shows astatistically significant decline since the measurements began in1979. This has occurred during a period when GCMs indicate that theearth should have warmed 0.6 C according to greenhouse models, and0.35 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 theNorthern Hemisphere. These are largely the regions that should showsulfate cooling! On the other hand, almost every latitude band inthe Southern Hemisphere, where greenhouse warming should operateunfettered, either shows no change or is cooling!
|Figure 5. Satellite temperature trends(degrees C/decade) by latitude bands. Note that there is cooling orno change everywhere except the mid-latitude land areas of theNorthern Hemisphere.|
The reliability of the satellite data is quite apparent when itsannual readings are compared to those from weather balloons between5,000 and 30,000 feet. This is well known. But perhaps moreinteresting is a comparison of winter minus summer temperaturechanges over the period of concurrence between the satellite andthe ground-based thermometers, which is 1979 to the present. Thecorrespondence is nearly as remarkable as is the agreement betweenthe satellites and the weather balloons.
Another way to appreciate observed change in a frame ofreference longer than the satellite record is to look at theground-based thermometers for the last fifty years.
All of these observations argue that the first alternativeproposed in 1995 by the IPCC - that the climate is lesssensitive to greenhouse changes than previously thought - ismuch more likely than the facile explanation that sulfate aerosolsomehow cancelled the warming.
|Figure 6. Temperature measured bysatellites (closed circles) match up nearly perfectly withtemperatures measured from weather balloons in the layer between5,000ft. and 30,000ft. (open circles).|
The Administration's Program: How Much Warming isPrevented?
As noted above, the most likely explanation for thenow-acknowledged warming deficit is that the sensitivity of globaltemperature to greenhouse effect changes was overestimated. Thereare several reasons why this may have been the case, but perhapsthe most compelling is that all of the general circulation climatemodels that have (to date) been referenced by IPCC containsubstantial "flux adjustments" for the poleward transport ofheat.
In plain language, these models have to be "adjusted"arbitrarily in order to keep them from producing unrealisticclimates. Generally (but not always) an additional increment ofheat moving northward is required. The obvious implication is that,left alone, the polar regions would become too cold and the tropicstoo warm.
A very few of the most recent models do not contain this type ofadjustment, including the one detailed in Figure 3. Notsuprisingly, it predicts considerably less warming thanits adjusted counterparts.
Table 1 gives the equivalent carbon dioxide concentration of theatmosphere, in parts per million (ppm), given a continuation of thecurrent exponential increase in emissions, and under the programproposed by the Administration. Under the Administration's plan, weassume that emissions reductions begin around 2004 and that theyreach 1990 levels by 2010 and remain constant after that.We assume that the entire world does thesame. We also assume that the time-behavior of theNCAR model is roughly linear through these increments of greenhousegas. This is a characteristic common to almost all climatemodels.
Projected Effective CO2 Increase
Table 1. The effect that the Clinton "plan" will have onatmospheric carbon dioxide levels and the resulting temperaturesavings (based on NCAR model results and the IPCC "best guess"emission scenario.)
Figure 9 compares the NCAR results for the next 50 years withand without the Administration program. The amount of "saved"warming is infinitesimal:0.13oC.It is doubtful that this change could even be extracted from groundbased temperature measurements, owing to problems with increasingurbanization and land-use alterations. However, it should beapparent in satellite measurements, which are accurate to withinplus or minus 0.01oC.
|Figure 9. Warming in the NCAR model with(dotted line) and without (solid line) the proposed Administrationprogram for the next 50 years. The total "saved" warming is 0.13degrees C, assuming emissions return to 1990 levels by 2010 andthen stay constant, and that the entire world does thesame.|
What Should be Done?
Emissions trading proposed by the Administration is simply a"hidden" tax that ultimately falls on the consumer and discouragesspending. Each consumer is impoverished a small amount whileemissions are forcibly reduced.
Is this what we really want? I think not. Rather, it might bewiser to allow people to keep their money. Many will invest theirfunds in technologies that will produce substantial energy atreduced cost. Some of these will produce few if any greenhouseemissions.
The lessons of technological history are clear. Each centurybrings about changes that are simply unanticipated butrevolutionary. 100 years ago, senior scientists and publicofficials worried that America would be deforested by the 1920s andthat disease would be rampant in urban areas because of thealarming increase in horse traffic. Amidst all this concern, theautomobile and the fossil fuel-powered economy were soon to appear.Its development was driven less by concern for the environment thanit was by the profit motive. Those who saw this opportunity didwell. If there was a substantial horse tax, there would have beenless to invest.
A similar argument could be made for nearly 200 years ago. Inthe early years of the 19th century, the U.S. governmentfretted over nascent Manifest Destiny. If it had gathered a team of"top scientists" to recommend how to move goods and people acrossthis vast nation, they would doubtless recommended a substantialand very expensive network of barge canals. Fortunately, there wasno massive tax levied to make this happen. But if there were, itwould have taken place just as the steam engine and fixed railtransit were being invented.
As we debate this issue and what to do, there are probably10,000 people tinkering and thinking about fuel cells, hydrogenpower, and undreamed-of exotica that will displace our currentenergy system. Let's save our citizens' money. Let's allow them toinvest in the future, take the risks and reap the rewards. Betterto do that than tax them to solve a problem that is not all thatemergent, and one that will nonetheless resolve itself faster ifonly 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. CambridgeUniversity Pres.
2. Houghton, J.T., L.G. Meira Filho, B.A. Callander, N. Harris,A. Kattenberg, and K. Maskell (Eds.)(1996). Climate Change1995: The Science of Climate Change. Cambridge: CambridgeUniversity Press.
3. Santer, B. D. et al. (1996). A Search for Human Influences onthe Thermal Structure of the Atmosphere. Nature,382, 39-45.
4. Michaels, P.J. and P.C. Knappenberger, 1996. Human Effect onGlobal 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 FudgeFactors, Science, 276, 1041
Statement of financial support from the U.S.government:
1996-1999 U.S. Department of Commerce. Cold Air Volume andPersistence in the Mid-Atlantic Region. $90,000.
1996-1998. U.S. Department of Energy. Greenhouse Influences onDiurnal Warming and Cooling Rates. $100,000.