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

Next, we will hear from Dr. Michael MacCracken, who is Division Director for Atmospheric and Geophysical Sciences at Lawrence Livermore Laboratory.

Dr. MacCracken.

STATEMENT OF DR. MICHAEL C. MacCRACKEN, DIVISION LEADER, ATMOSPHERIC AND GEOPHYSICAL SCIENCES DIVISION, LAWRENCE LIVERMORE NATIONAL LABORATORY, LIVERMORE, CA

Dr. MACCRACKEN. Thank you. It is a pleasure and a challenge to come before you and try and talk about knowns and unknowns, especially when so many aspects of this issue are raised.

I might just say that what we do as a group at Livermore is focus on perturbations to the atmosphere and modeling such perturbations. Those range from radionuclide releases like Chernobyl, to Kuwaiti oil fires, to nuclear winter, to ozone depletion, to greenhouse gases. We try and provide a balanced perspective on what happens and what might happen and raise those issues for discussion.

We think it is important to make sure there is a consistency across a lot of these different cases. One of the things that is unfortunate in a lot of the reports that come out is they focus on one aspect of an issue, but then it does not turn out to be consistent with other aspects.

I guess I should also confess that I think I was the one who promoted the notion in 1975 that there be a carbon dioxide research program in the Energy Research and Development Administration, which was the predecessor to DOE. I sort of recently went back over that letter, and it was interesting. It was basically a plea that they start a program, that they circulate it to a lot of experts. At the time there was a lot of discussion about would there be global cooling, and yet the consensus of experts from around the world at that time was that they ought to get started on a program, and they did. I basically have been involved in their program ever since.

In the few minutes that I have, I want to try and address a few points. First I want to offer a few comments on the underlying causes of this polarization. Some people call it politicization, but I want to just offer a few comments on that.

Second, I want to mention a few points on which I think there is broad agreement in the scientific community. You don't often hear that. Scientists love to battle each other in a lot of different ways. There are uncertainties, but there are points on which there is great consensus.

Third, I want to maybe make a couple of brief comments on climate uncertainties and how that relates to the impacts issue and to the responses to the problem that you are considering.

Then I guess, fourth, I would urge, as one part of a solution to this effort, some more emphasis in the U.S. global change research program about centers to try and synthesize and integrate results. That is happening in some of the other countries around the world.

It hasn't happened as much in the United States, and that might help in the debate.

With respect to this first point about this polarization of the debate, I think it is important to recognize that there are three different parts to the problem. That is how IPCC has considered it and I think very well. That is, there is the direct chemical and climatic effects. That is very much a scientific issue. There is the consequent impacts on the biosphere and on human activities. That is a very difficult issue that gets into biology and ecology and social impacts. And then there is the issue of possible responses and options to address these issues.

It is my belief that mixing of these three aspects has been an important contributor to polarization of the debate. It turns out it is very difficult to do the impacts issue, to say what this is going to mean to society. So, people look back at the science and then take the jump to the economic effects or the policy responses, and they do this with two differing perspectives.

One is a group that focuses-they are very cautious about the environment, and they focus on worst case scenarios, sometimes on extrapolations. They very much urge that you take action because of the uncertainties. Because we don't know what the future will be, you should take action.

There are also those who are concerned about endangering the economy, and they focus on every contradiction that they can find in scientific understanding.

Now, it is important to realize that both aspects are important to society, and you have to somehow balance those. But what is happening is each side in that seems to me to be taking extreme examples from what the other side says, then taking devastating potshots at them and dismissing the problem as a whole. I do not think that is very helpful in what is going on.

Well, let me just comment on a few things that I think there is a agreement on. This comes out of modeling studies, looking at past climates, lots of different ways. These are not just results of general circulation models.

I think there is absolutely no doubt that we are changing the atmospheric composition in a way that is just totally unprecedented. We are doing an experiment that nature hasn't done. The last time that CO2 concentrations have been as high as we are sort of projecting for the next century is sometime many millions of years ago, and there are attempts to go back and look at how different the climates were back then, and they were quite different.

The second point is that atmospheric composition is a very important determinant of the climate. It controls the earth's temperature. Without having atmospheric composition changes, we just can't explain past climatic changes.

Third, despite their shortcomings, computer models have many strengths. There are many things that they do well in reproducing the climate. They are not often talked about, but there are many strengths. There are also weaknesses. But models encompass all of our understanding, to the best that we can put it in. We all keep working on them to try and improve them, but it is the sum total of our understanding to a large extent.

If we then use these models with their shortcomings and try and go back and look at what atmospheric composition will do, it is clear that past and the anticipated changes in the atmospheric composition are going to commit the world to significant climate change. Now, the models also indicate that other factors like volcanic aerosols and sulfate aerosols and ozone depletion will alter the climate, and we test the models against those things. There is reasonable agreement in that regard.

With respect to the warming, there is broad agreement that warming has occurred of about a half a degree Centigrade. The problem is not that it can't be-well, I guess the way to say it is we can't from that record get detailed quantitative association from the greenhouse gases that helps us truly pin down what we know about the future, but it is certain that some of that warming is related to greenhouse effects. It has to be. If that were not the case, we just wouldn't understand how the whole system works, and the model wouldn't work for a lot of different reasons. But we have to do some reconciliation of the greenhouse effect with the other factors affecting the climate.

Then finally, I think there is broad agreement that the warming influences of greenhouse gases over the next several decades on average you can't predict decade to decade-are going to increasingly exceed the cooling influences of aerosols and some of these other factors. We have basically set our planet on an unprecedented path that will lead to increasing and long-term change.

Let me comment just very briefly about potential impacts. There is a lot of discussion about whether it is beneficial or not or detrimental. The main argument that it might be beneficial is that the CO2 increase is beneficial to plants and will make agricultural crops grow better, and that may or may not be true, as it turns out. In the U.S. economy and in a technologically advanced society, you may be able to take advantage of that.

But there is a range of other important topics where it is hard to see how the effects can be beneficial. Water resources is one, and that is certainly a very important one in California if a rising snow line occurs. Coastal habitats with rising sea level and island habitats, ecological systems, and even the human environment of it becoming warmer. You try and ask people in low latitudes how they will deal with warmer climates, it will be very difficult. And in agricultural regions with just one-crop economies, as the climate shifts, it will be very difficult.

Then with respect to responses, I think it is important to realize that fossil fuels provide more than 90 percent, 80 to 90 percent, of the world's energy. The global population is growing. There is an interest in raising the standard of living. The best scientific estimates are that to stabilize the atmospheric CO2 concentration at its present level requires not a 10 or 20 percent cutback, which is what people are sometimes talking about, but about an 80 percent cutback, a dramatic change in use of fossil fuels.

I think what seems to get let out in a lot of the discussion is that oil and gas we will sort of use up in the next probably 50 to 60 or 50 to 100 years. Fossil fuel then becomes coal and oil shale, if we choose to use it. If we are going to go to nonfossil fuel technologies,