reference gas. The same ocean-atmosphere carbon cycle model as in IPCC (1990) has been used to relate CO2 emission to concentrations. Table 3 shows values for a selected set of key gases for the 100 year time horizon. While in most cases the values are similar to the previous IPCC (1990) values, the GWPs for some of the HCFCs and HFCs have increased by 20 to 50% because of revised estimates of their lifetimes. The direct GWP of CH, has been adjusted upward, correcting an error in the previous IPCC report. The carbon cycle model used in these calculations probably underestimates both the direct and indirect GWP values for all non-CO2 gases. The magnitude of the bias depends on the atmospheric lifetime of the gas, and the GWP time horizon.

Indirect Global Warming Potentials.—Because of our incomplete understanding of chemical processes, most of the indirect GWPs reported in IPCC 1990) are likely to be in substantial error, and none of them can be recommended. Although we are not yet in a position to recommend revised numerical values, we know, however, that the indirect GWP for methane is positive and could be comparable in magnitude to its value. In contrast, based on the sub-section above, the indirect GWPs for chlorine and bromine halocarbons are likely to be negative. The concept of a GWP for short-lived, inhomogeneously distributed constituents, such as CO, NMHC, and NO, may prove inapplicable, although, as noted above, we know that these constituents will affect the radiative balance of the atmosphere through changes in tropospheric ozone and OH. Similarly, a GWP for SO2 is viewed to be inapplicable because of the non-uniform distribution of sulphate aerosols.

PART III: SUMMARY

It is clear in the 1992 IPCC supplement that there are significant scientific uncertainties associated with our assessment of global climate change. Resolution of these scientific uncertainties will take years to decades even with comprehensive research programs such as the U.S. Global Change Research Program (USGCRP) that are focussed on resolving the key IPCC scientific uncertainties; i.e:

• clouds, which control the magnitude of climate change

• sources and sinks of greenhouse gases and aerosols, which control future atmospheric concentrations, hence the magnitude of climate change

⚫ oceans, which control the timing and regional patterns of climate change land-surface hydrological processes, which control water availability and regional patterns of climate change

• cryosphere, which affects sea level rise and regional patterns of climate change ecological systems, which affect, and are affected by climate change

The USGCRP will provide the scientific information needed to formulate mitigation and/or adaptation policies.

Consequently, near-term national and international policies will have to be formulated recognizing that these scientific uncertainties exist and that the magnitude and rate of global warming may have been overestimated or underestimated. The scientific evidence for global warming, coupled with the long atmospheric lifetimes of greenhouse gases like carbon dioxide, suggests that the U.S. approach of identifying and implementing energy conservation, energy efficiency, and reforestation measures that reduce net greenhouse gas emissions is prudent.

The CHAIRMAN. Thank you very much, Dr. Watson.

Next we will hear from Dr. Richard Lindzen, who is Professor of Meteorology at Massachusetts Institute of Technology and who is also on the Scientific Advisory Board of the Marshall Institute. Dr. Lindzen.

STATEMENT OF DR. RICHARD S. LINDZEN, ALFRED P. SLOAN PROFESSOR OF METEOROLOGY, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA

Dr. LINDZEN. Mr. Chairman, members of the committee, I am pleased to be here.

I am on the Scientific Advisory Board of the Marshall Institute. I must say immediately that I have seen this document no sooner than the rest of you and was not an author. I have just read it. I must say that in connection with this-and I will only say a few words-I tend to agree with Bob Watson with one possible ex

ception. I have great regard for Bill Nierenberg, Fred Seitz, who I think were involved, and I think as a document, it is an extremely different document from the IPCC. There is no question that it is the document a few very distinguished scientists approaching information that all of us have to approach and reasonably looking at problems with it. They reach conclusions in some instances that I don't agree with, and in some instances, I feel they have bent over backwards to accept the common scenario. In some instances, I think they have gone the other way. So, I don't feel that there is a profound bias in that. They are pointing to obvious discrepancies that people should be aware of.

But getting back to the real scientific issue, I think Bob laid out certain things that I think people are not aware of, especially when they claim that there is clearly an impact of man on climate, meaning global climate. The IPCC doesn't say that. It isn't hundreds of scientists agreeing on that contention.

Let me make a number of remarks that I think are widely accepted and might give a different flavor, although I think Bob mentioned some of them.

If there is one statement that virtually everyone in the atmospheric science and climate community agree on, it is that the observed temperature variation over the last century is indistinguishable from natural variability. One of the improvements in models is that if you run models with no change in CO2, they also exhibit the same measure of variability. That is to say-and this is extremely important for I think Senator Akaka and so on-whether one likes it or not, climate will change. It always has and it probably always will, and man and other species will have to deal with it as they can. That has nothing to do with our role, and I know of no proposal to prudently avoid this natural variability.

Now, another issue where I have grown to think it is highly politicized is the nature of the greenhouse effect itself. That surprised me a little bit because that would seem like basic science. There is a picture in the IPCC report in the update. It is also in my written testimony. It shows the greenhouse effect. The IPCC labels it as simplified. It shows the sun illuminating the earth. It shows the earth trying to radiate the infrared. It shows the gas absorbing it and sending the radiation back to earth.

One wouldn't think of that as a political diagram, but it is. It is because the simplification involves rejecting everything except radiation. Hence, it makes the adding of greenhouse gases look like it inevitably must heat the atmosphere. Now, the IPCC authors know better. Most of this panel knows better. I know better than that. The atmosphere like any other thermodynamic system can carry heat by motion. It can carry heat by radiation. Indeed, if it only had radiation, the earth today would have an average temperature close to 160 degrees Fahrenheit. The greenhouse effect is extremely ineffective. Not only that, due to motions, it is entirely possibleand we have done numerous experiments on this-to increase the amount of greenhouse gas and get a cooler system. Indeed, increasing water vapor in the Arctic leads to cooling, not heating.

Now, why is this diagram political? Because it takes a complicated issue with a multitude of answers, gives it to the public and says it is inevitable. See? I asked the Chairman of the IPCC, Bert Bolin,

why, given they had another diagram that was more accurate, did they use this one. And he freely said to use the real diagram would make people confused. They wouldn't think it is inevitable. That is politicization.

Now, let's continue. Carbon dioxide. It is the gas whose increase is supposed to give rise to warming. Models agree that a doubling of carbon dioxide alone will give rise to a warming on the order of 1 degree. Different calculations get between 0.5 and 1.2. That itself will lead to no monumental changes, including the 26-inch rise in sea level which is asserted, but by no means real.

Why are we worried about something this small? Why is it so small? Of course, what the public frequently does not realize is that carbon dioxide is a minor greenhouse gas. The major greenhouse gas is water vapor, and if you took away all the carbon dioxide in the atmosphere, you would still have 98 plus percent of the greenhouse effect.

It is interesting, just this month in Journal of Geophysical Research, a number of scientists attempted to simulate ice ages by reducing carbon dioxide as observed. This is Verbitzky, but McElroy has done it at Harvard as well. They do not get within 10 percent of what they have to with that. It's just not important enough.

Now, again, why do models get more than this? We heard numbers like 4 degrees, 5 degrees for a doubling of CO2. That is due to what are called feedbacks. The models used amplify any perturbation. They amplify it by a lot, a factor of 4. That is a big amplification. The question is why. It turns out the biggest feedback is that due to water vapor. It turns out in all the models, when you warm the surface, water vapor increases at all levels. That is very important.

Now, the IPCC in its front end, the policymakers' summary, states categorically that they are absolutely sure about this. The update has dropped that, most fortunately, but the IPCC report itself internally says this is a matter of great doubt. One of the problems has been the discrepancies between the IPCC text and the IPCC summary.

The fact of the matter is that no model will give large warming without positive feedbacks, amplification, and I will come back to that because most of them are extraordinarily uncertain and even unlikely.

I would ask you to consider a situation which Science magazine referred to as metaphysical by way of criticizing. Namely, do you think it likely that the earth's climate system is a system which takes every perturbation and magnifies it greatly into catastrophic proportions or is a system which will attempt to stabilize its response to the perturbations it is inevitably exposed to? The current view is we live in a world just waiting for the least perturbation to go crazy. Politically, psychologically it may be true. Physically I don't think so.

Now, another issue, which there is again widespread agreement on, large amplification in the climate system also has an implication for the ocean delay. The larger your amplification, the longer the ocean delay. This is a result Jim Hansen produced some years ago with his group.

Now, what the IPCC fails to mention, but which is absolutely true, is that if you expect 4 and a half degrees for a doubling of CO2, it will take about 160 years to reach two-thirds of that. Now, that would mean that if the atmospheric CO2 doubled by 2100, we would see very little change. If you look at the IPCC, you see about 3 degrees change by 2100 in their time-dependent calculations. Do you know how that happens? Their effective CO2 has quadrupled by 2100. In fact, what the call the business as usual scenario was designed to give them a doubling by 2030 and a quadrupling by 2100 because they knew that without a quadrupling you wouldn't even see anything close to the equilibrium values for a doubling by 2100.

Now, the question finally is do we expect CO2 to behave that way. Bob Watson said the time scale for CO2 is over 100 years. It is a well-known formula that the percentage of a gas you expect in the atmosphere will bear a certain relationship to the response time that Bob mentioned and the rate at which emissions are growing. A hundred years would tell us that about three-quarters of the CO2 emitted would stay in the atmosphere. The observation that less than half has stayed in the atmosphere tells us that the system is responding much faster. And the recent studies including the biosphere concur in this, and they say that even business as usual emissions will not double CO2 by 2100. So, we are already exaggerating I think at that point.

Now, I mentioned the water vapor feedback. Let me say just a very few words on that. The physics involved in determining water vapor are missing in all current models, and that is a statement. You can confirm it in the IPCC. Essentially we are learning that the amount of water vapor in the atmosphere depends on how much ice and water are thrown up by deep clouds. It is impossible to transport water vapor by large scale circulation because if you raise it up, the air gets cold and it condenses out. If you bring it down, the air gets hot, and it dries. So, you have to bring water and evaporate it locally.

Models don't have that. The NCAR group, in fact, has established that numerical errors play a major role in determining water vapor. Remember, without this feedback, you do not get more than a degree and a half warming for a doubling in equilibri

um.

If the reason the models are giving a warming is numerical artifact, then we are left with a situation where we don't observe it and we don't have the wherewithal to have predicted it. There are extant tests that can be conducted, and they suggest that it is a negative feedback, but the real question is how does one respond to something for which one has neither the theory nor observations, only an amorphous fear. How does one know the policies one chooses are relevant to it? How does one even know what prudence is? Thank you.

[The prepared statement of Dr. Lindzen follows:]

PREPARED STATEMENT OF DR. RICHARD S. LINDZEN, ALFRED P. SLOAN PROFESSOR OF METEOROLOGY, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA

SUMMARY

Given normal climate variability, we may reasonably expect that there will be future climates both warmer and colder than the present regime. This, however, hardly supports the current fear that increasing greenhouse gases in the atmosphere will lead to catastrophic warming. The IPCC Scientific Assessment 1 as well as the current update (Houghton, et al, 1990, 1992) both recognize that temperature changes over the past century (a net warming of 0.45 °C+0.15 °C) are consistent with natural variability and smaller than what would be expected for models predicting over about 1.3 °C equilibrium warming for a doubling of CO2-assuming all the change over the past century were due to CO2.2 This, of course, seems unlikely since the bulk of the warming occurred before 1940. Thus, the data neither suggest nor provide support for current warming scenarios. Neither do simple greenhouse considerations. All other factors remaining constant, the equilibrium greenhouse warming, resulting from a doubling of CO2, is estimated to be between O.5 °C and 1.2 °C (Ramanathan, 1981, Lindzen, et al, 1982, Sun and Lindzen, 1992a, Houghton, et al, 1990). These values may seem small, but CO2 is only a minor greenhouse gas. If all CO2 were removed from the atmosphere, water vapor and clouds would still provide over 98% of the present greenhouse effect. Predictions of larger equilibrium warming depend crucially on positive feedbacks from water vapor, cloud cover, and surface albedo (due to snowcover). Of these model feedbacks, water vapor is by far the largest. As it turns out, the physics of the water vapor budget is largely absent in current models. Indeed, in most (if not all) models the water vapor feedback is readily identifiable with a calculational error. Thus, there is no theoretical basis for the catastrophic warming scenarios as well. Indeed, there are reasons to believe the feedbacks are negative, suggesting the equilibrium response to CO2 doubling may well be much smaller than the direct response (Sun and Lindzen, 1992a,b). Finally, the term 'equilibrium' should be explained. It refers to the response achieved over an infinite time. In point of fact, the actual response time (largely determined by heat transport into the ocean) increases proportionally to the expected equilibrium response (Hansen, et al, 1985). In fact, a model predicting a 4.8 °C equilibrium warming for a doubling of CO2 would only have reached 2/3 of this warming in about 160 years. It is interesting, in this regard, to note that the models examined in the IPCC Scientific Assessment produce warming by 2100 almost equal to the equilibrium response of these models to a doubling of CO2; in these models, however, CO2 has quadrupled by 2100. Had it only doubled, the predicted warming would have been much less. This is illustrated in Figure 1 where I show the expected warming for models with equilibrium responses to a doubling of CO2 of 3.6 °C and 4.8 °C. Such models are at the very high end of the expected responses given by Houghton, et al (1990, 1992). Results are shown for scenarios where CO2 either doubles or quadruples by 2100. In the latter case, fossil fuel reserves will be nearly exhausted.

EXPANDED DISCUSSION

We will expand on some of these points in the remainder of this statement. However, before even discussing 'greenhouse theory', it may be helpful to begin with the issue that is almost always taken as a given: namely, that CO2 will inevitably increase to values double and even quadruple present values. Figure 2 shows the behavior of CO2 since about 1800. Before 1958, the record is based on the analysis of ice cores. After 1958, it is based on direct atmospheric sampling. Clearly, CO2 has been increasing. Prior to 1800 the density was about 275 ppmv (parts per million by

1 IPCC refers to the Intergovernmental Panel on Climate Change. This panel is sponsored by the UN's World Meteorological Organization and the UN Environmental Program. The panel consists in members posted by governments. University scientists tend to be very underrepresented-if only because most such scientists have neither the time nor the funds to participate. For example, the recent update involved meetings in Bristol, England, Guangzhou, China, New York and Geneva-all within a six month period.

2 The update suggests that the expected warming was to some extent cancelled by cooling resulting from cloud brightening by sulfates. The update, therefore, suggests that the past record might be consistent with an equilibrium response to CO2 doubling of almost 2 °C. While this is also not a catastrophically large warming, the IPCC estimate is based on the work of Charlson, et al (1992) which probably overestimates sulfate loading by a factor of 3-4 (Seinfeld, 1986). We are, therefore, sticking with the 'uncorrected' value of 1.3 °C from the original IPCC Scientific Assessment.