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Mr. ROHRABACHER. I believe that is a fairly substantial charge, Dr. Michaels. And we will now move forward with some questioning.

First of all, before we go into questioning, let me give you the opportunity to ask a question or two of each other, and if I could just ask this: that we make this as direct as possible-answers and questions.

Do either of you have I mean, these are pretty substantial charges that Dr. Michaels is saying-do you have any questions, or vice versa?

Dr. MAHLMAN. If I may, Mr. Chairman

Mr. ROHRABACHER. Yes, sir.

Dr. MAHLMAN. Yes, thank you.

I agree with Dr. Michaels that the observed record does indicate a climate sensitivity lesser than that implied by the models in the past.

I do not agree that his analysis is logical or straightforward in that he is appealing to a comparison of a realistic case, namely the last 15 years, to an idealized increasing CO2 case, and that leaves out the effect of sulfate aerosols, as he properly points out. It also leaves out the fact that the satellites are now known to be seeing the strong ozone losses that have happened in the upper troposphere and the lower stratosphere.

Mr. ROHRABACHER. Do you have a specific question for him that might

Dr. MAHLMAN. My specific question is to speak to an assertion that he made. Okay?

And therefore I would submit that indeed it is true that it is most likely that aerosols are producing a temporary offset to the global warming problem, but I do not accept that this argument is as clear as he is arguing it is, merely because the comparison is not fully straightforward.

Dr. MICHAELS. Excuse me.

The ozone or the aerosols tend to lie in the bottom 5,000 to 7,000 feet of the atmosphere. That is the satellite's best temperature sense is from 5,000 feet to 30,000 feet in channel 2R. It is above the aerosol layer.

So you cannot say that the aerosols are what is preventing the warming in the satellite.

And you also cannot say that it is the ozone depletion that is preventing the warming in that record because most of the ozone depletion takes place above the 300 millibar layer, in fact, above the troposphere.

We had this discussion, I should say, Mr. Chairman, at our meeting on October 13th, 1994, and that discussion, which I have recorded, states the following:

The argument was made that, “Oh, you just have to dismiss the satellite data because ozone is what is compromising it." And a response was made.

Ozone is a direct radiative effect and it changes much from year to year. In the years in which the ozone shows a low spike, is that reflected in the satellite temperature?

Answer. "Oh, no, no, no. It is just a trend, you know."

Mr. ROHRABACHER. Dr. Michaels, maybe-well, let me just ask Dr. Guerrero if he something to throw in now as rebuttal or observation.

Mr. GUERRERO. Why not.

Mr. ROHRABACHER. You know, by the way, I am sure that there are people in the scientific community that will understand every single thing that you two fellas just said.

Dr. MAHLMAN. We hope so.

[Laughter.]

Dr. Guerrero, would you?

Mr. GUERRERO. I would just point out that an important consideration to keep in mind when thinking about the models and their admitted limitations, which I think both of the panelists will agree, that there are limitations.

That the modelers themselves recognize those limitations and in fact conduct sensitivity analyses and assessments and make what they call flux adjustments to reflect the fact that models are indeed somewhat out of sync with when you go back and you look at the climatic record, they will be off to some extent.

And that that is a normal process. But the fact that modelers do that makes the models better in terms of the predicted capacity by removing error than compounding that error.

Dr. MICHAELS. I have a question. I did not get to ask one.

Mr. ROHRABACHER. Let's do this. Let's go through our regular questions and answers. Then we will have one final round of rebuttalism at the end.

I would like to ask about the-and why I stopped you, doctor, is that in the middle of your statement, to have you repeat that, is that you believe that the global warming and greenhouse effects basically are tied, and that there is no question in your mind, to human activity?

Dr. MAHLMAN. What I said, Mr. Chairman, is that the increasing greenhouse gases, particularly carbon dioxide and chlorofluorocarbons are specifically attributed to human activities, was my specific statement.

Mr. ROHRABACHER. But we are talking about global warming itself being a product specifically of human activity. That is what I am getting at.

Dr. MAHLMAN. Okay.

Mr. ROHRABACHER. Is that your position that if there is global warming, if after, if in the end people can agree on that, which is not something necessarily we agree on, an assumption we agreed on at the beginning of the hearing, but we will see about at the end of the hearing, but you, it is your position that that global warming is tied directly to human activity?

Dr. MAHLMAN. My position is, and my testimony reflects this, sir, that the observed warming over the last century is not unambiguously attributable to the greenhouse effect. Okay? There are alternative explanations.

My opinion is that there are virtually no credible counterhypotheses. Natural variability is often assumed or asserted to explain that. But there are some significant inconsistencies in that assertion.

So I cannot say with absolute certainty that the observed record is a reflection of greenhouse warming at this time.

Mr. ROHRABACHER. Repeat that last statement?

Dr. MAHLMAN. I cannot say, with absolute certainty, that the observed temperature change over the last century is ascribable to human-caused greenhouse warming. I cannot say that.

I just say that there is no plausible hypothesis that is nearly as credible.

Mr. ROHRABACHER. So you are saying that it is most likely that

Dr. MAHLMAN. Yes, indeed.

Mr. ROHRABACHER. When you have novices like myself looking at different arguments, and you hear someone say, well, you know, one volcano, and I will give some volcano, Mt. whatever it is, wherever it is, can spit this much into the air, and compared to what all of the industries of the earth produced in the last ten yearspeople are telling this all the time-that there are these natural causes that actually far outweigh anything that we have done in the industrial world for the last few years.

Should I just discount that as a charge?

Dr. MAHLMAN. Yes, I believe you should. Science is not a game of handwaving or a game of debating points; science is a game of numbers. And the problem with the volcanic type explanation is that they are transient things. They come, they blast stuff into the atmosphere and it causes a very big effect for a few years, and then it gets washed out and goes away. Okay.

So I can think of none of those natural causes that are nearly as credible as the argument that greenhouse warming is producing the observed warming.

We do indeed argue about whether or not this is completely consistent with what the models are predicting, as Dr. Michaels properly points out.

Mr. ROHRABACHER. Dr. Michaels, could you comment on that?

Dr. MICHAELS. Yes. The one point of disagreement, and I do not think it is particularly large, is that in the land-based temperature record, which begins in the late 19th century, that record begins in a very cold period that some people refer to as the end of the little ice age.

And so when we look at the temperature history, say of the northern hemisphere which is supposed to be most responsive to greenhouse gases, you see a warming that occurs mainly prior to

1940.

And then actually between the mid thirties and now, there is not that much net warming. That early warming can only have very little to do with the greenhouse enhancement, while the last warming could conceivably be that.

Be that as it may, Dr. Mahlman is right. It is not a game of debating points and it is a game of numbers.

And let us discuss those numbers for 15 seconds, if we could.

I want to elaborate upon the model that I was speaking about and about the old models.

The model that best tracked the past, according to the intergovernmental panel on climate change, is the model that only has 1.3

degrees of warming remaining in it for equilibrium doubling. That is somewhere around the year 2100.

Now we might make the argument that CO2 is going to continue to go up and up and up and up. But that means that you are going to forecast the energy strategy of this society 100 years from now. Imagine if you would have made the forecast 100 years ago. You would have gotten a panel of top scientists and they would have said, "All credible scientists agree Washington will be ten feet deep in horse chestnuts by the year 1995." And that would have been the proper science.

If you had a visionary that said, "No, there is going to be a personal transportation system, life span's going to double, corn yields are going to go up by a factor of five." You would have said that person was insane.

But that is the game that we are playing when we try to say what is going to happen beyond doubling CO2.

Other end of question; it is a game of numbers. In 1992, when the Rio Treaty was signed, and the climate models did not have sulfate aerosol in them, I believed that people who testified in front of this Congress knew that the error was as large as it was. If they did not, they did not know their own models.

Why was that not told to this Congress?

Mr. ROHRABACHER. One thing. Could you go through the importance of that particular thing again, because I am not sure that I fully understand the importance of leaving that element.

Dr. MICHAELS. There was a change between 1990 and 1992, and the nature of climate modeling in general.

In 1990, to save on computer time, the climate models would what we call "instantaneously" double their greenhouse effect. In other words the CO2 in the model atmosphere would be down here, and then would go like this, and the climate would respond up like this, producing an average warming in the five main models of 4.2 degrees.

That is unrealistic because CO2 goes up gradually.

And for the 1992 supplementary update, which was produced specifically to back the Rio Treaty, a series of models were developed in which the CO2 increased gradually. One percent per year was the forcing change in the model.

That model becomes very testable against reality. And when you make the assumption that that model was producing the correct temperature when the greenhouse effect started to take off-and if you do not make that assumption, you are saying it does not work anyway-if you make that assumption and track the CO2 increase in the model versus the northern hemisphere temperature, you get a difference of about 1.2 degrees between today's temperature and what was forecast.

And now, in the latest issue of Nature Magazine, J.F.B. Mitchell says the very, very same thing. He says the minimum error in his current model, which is very similar to the one that based the U.N. report, his model without sulfates, the minimum current error is 1.3 degrees, I am sorry, the minimum warming is 1.3 degrees in the model and the maximum is 2.3, and the observed value is 0.5. Mr. ROHRABACHER. Over a period of what time?

Dr. MICHAELS. Between 1900 and now.

So that he is saying that it is off by a factor of between 2 and 3. Those were the models that based the treaty.

I believe it was known in 1992 that that error was there.

Mr. ROHRABACHER. We are going to give Dr. Mahlman a chance to say, he is anxious to say something, and then we will go on to Mr. Roemer's questions.

Dr. MAHLMAN. It was very clear that the first full coupled models with transient scenarios were run before you said they were. But the real point is that, yes, it was realized that the best estimates for models did disagree with the observed global surface mean temperature increase.

And the assertion now that we have found this lower sensitivity that Dr. Michaels just made is not supportable based on the evidence, because there are very key parts to the climate system that have not been quantified in that argument, including the affect of sulfate aerosols that he quotes and the affect of natural variability. So that it could be larger than that; it could be smaller than that.

I have been betting for a long time that it is more probable that the realized warming would be in the lower half of the predicted range, and have said so publicly for a long time.

Mr. ROHRABACHER. It could be lower than that, it could be smaller than that?

Dr. MAHLMAN. Yes.

Mr. ROHRABACHER. All right.

Mr. Roemer?

Mr. ROEMER. Thank you, Mr. Chairman.
Thank you gentlemen, for your testimony.

Dr. Michaels, despite some disagreement on interpretation of models sensitivity, aerosol effect, and so forth, I would gather from your testimony that you still would be a strong supporter of continuing to study the potential effects of greenhouse?

Dr. MICHAELS. Oh, yes. And more than that, I have written very recently in a public venue, and I may get thrown out of this room for saying this, that it is very, very important that we continue our efforts to monitor the planetary temperature.

If we lose, I say that because I believe the models are being, that models in reality are converging upon a low, benign warming. Now if we do not maintain the check data, the ground-based network, those satellite MSUS, boy, those are really important.

Mr. ROEMER. So despite some disagreements that we may have in the scientific community, you feel that this Committee should continue to put the money and the research materials together to study this problem.

Right, Dr. Michaels?

Dr. MICHAELS. I believe that is the case. But that does not mean that you do everything that everybody says.

Mr. ROEMER. So let me give you some examples.

If this Committee wou'd decide to cut NASA, the PM and the AM satellites, if they would cut NOAA, the global climate program by 25 percent, if they decided to cut renewable energy resources in research by 40 to 50 percent, totaling about 50 percent cut in these programs, how does that give the scientific community, whether

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