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The issue for debate is human influence on climate and the ability to change its future direction.

Despite the uncertainties surrounding the attempt to understand the Earth's climate, the Administration's position going into the Kyoto conference is that the science is settled. As a result, none of the scientists who have different views on this issue from the Administration participated in the conference.

For this Administration, which prides itself on diversity, this conference was evidence that the diversity of scientific thought is not included in the mix.

Nevertheless, it will be clear from the testimony today, although scientists agree on the warming effect of greenhouse gases, there are a wide variety of views on how such climate influences such as clouds, water vapor, and even the sun affect the process.

So the issue we must face is whether the state of the science today is sufficient to back the proposed treaty or whether more research is necessary.

I would like to point out once again that this Subcommittee and the Committee on Science are on record in strong support for funding climate change research. Our increasing sophistication in shortand long-term range weather prediction pays off in savings of lives and property. I will continue to support research funding in this area during the budget process and, I think, that will hold true for most of the Committee members.

Before I introduce today's panel of witnesses, let me turn to my friend from Indiana, the distinguished Ranking Minority Member, Mr. Roemer, for his opening remarks.

Mr. ROEMER. Thank you, Mr. Chairman. I'm pleased to be here with the Subcommittee this morning, and hopefully will contribute to what I think is one of the most important environmental decisions we will make this decade: how we will respond to the threat of global warming.

This decision is, by any measure, a daunting one. The cost of greenhouse gas reductions may equate to several percent of the world's GDP. The economic penalties of global warming unchecked is also several percent of the world's GDP.

This decision must be made against a backdrop of large scientific uncertainty. After an exhaustive review of the science in 1995, the Intergovernmental Panel on Climate Change [IPCC] concluded that, "The balance of evidence suggests that there is a discernible human influence on global climate." But how much proof is needed to enact the policies that will be on the table in Kyoto? Should we demand evidence beyond a reasonable doubt, a preponderance of evidence, or some other standard of proof? Science has no clear guidance for us on this, "How much is enough?" question.

Clearly, we are exposed to media reports every day that should concern any responsible policymaker. Most of the public now believe that something is happening to the climate. Increasing surface temperature measurements over the past century are going up, changes in mountain glaciers around the world, changes in arctic and antarctic sea ice, rising sea levels, and comparisons with the geologic past, all suggest that we may be experiencing the early stages of a human-induced warming epoch. On the other hand, some have pointed out that it is difficult to rationalize satellite

data collected over the past 20 years with this other data. This remains an active area of scientific debate.

Thus, the balance of evidence may support the need to consider greenhouse gas reductions, but not all evidence. Unfortunately, this will always be the case. Science can never provide a perfectly certain answer and policymakers will always need to make decisions in the face of that uncertainty.

Today's hearing will provide the opportunity to examine the state of this balance of evidence that the participants in the upcoming Kyoto meeting will be considering. Have the statements of the IPCC held up over the past 2 years? Is the science stronger today than it was 2 years ago or should we be concerned over the uncertainties raised by the satellite data?

Some proponents have suggested that the scientific debate for global warming is over. It is unlikely that the debate within the science community will ever be over, but is it sufficiently mature that we can consider policies for greenhouse gas reductions?

Today's hearing, together with the hearing later this week on the economic aspects of global warming, will help to inform the debate within Congress. Over the next several years, Congress will be charged with providing the necessary resources to continue critical research programs needed to understand global warming. We will also be charged with implementing whatever policies flow from the commitments we make in Kyoto regarding emissions reductions.

I hope this hearing will help us understand the state of the science surrounding the global warming debate, the risks we may face, and the options we may have to deal with this threat.

Mr. Chairman, certainly, a few weeks ago we had a hearing on El Nino, and nobody on this panel doubted that there was some kind of impact from El Nino on the weather changes in the world. Certainly, in the State I come from, Indiana, when we look at such things as the "U.S.A. Today" weather page, in October, in Indiana it is certainly unusual that, I think, 80 percent of the United States has 80 and 70 degree weather in October; and this is not an advertisement for Ted Turner and his weather station or "U.S.A. Today." But certainly, it is interesting, and certainly the surface temperatures that we're now reading across the world lead us to some kind of scientific analysis that might be different from decades and centuries past.

So I am interested in this scientific debate and very interested in what the panelist may have as a recommendation for us today. Chairman CALVERT. I thank the gentleman for his testimony. We have today with us a distinguished panel of scientists who have many years of experience in the study of climate change. First, Dr. Roy Spencer is the Senior Scientist for Climate Studies at NASA Marshall Space Flight Center in Huntsville, Alabama; Dr. Aristides Patrinos directs the Office of Biological and Environmental Research for the Department of Energy, where he is also an Associate Director of Energy Research; and Dr. Alan Robock, has been on the faculty for the Department of Meteorology at the University of Maryland for 20 years; and, finally, Dr. Ronald Prinn is the Director of the Center for Global Change Science at the Massachusetts Institute of Technology, where he is also TEPCO Professor of Atmospheric Chemistry.

It is the policy of the Science Committee to swear in all of its witnesses. Will the members of the panel please stand and raise your right hand.

Do you solemnly swear that the testimony you're about to give is the truth, the whole truth, and nothing but the truth?

Mr. SPENCER. I do.

Mr. ROBOCK. I do.
Mr. PRINN. I do.

Chairman CALVERT. You may be seated.

Gentlemen, without objection, your full written testimony will be entered into the record. I would ask that you summarize your testimony for us in 5 to 7 minutes, it will help us leave time for questions and we can expect, probably, to be interrupted for votes today, so I apologize for that.

Dr. Spencer, your opening statement.


Mr. SPENCER. Thank you, Mr. Chairman, and I would like to thank the members of the Subcommittee for this opportunity to present my views on global warming.

Probably all climate scientists will agree that increases in atmospheric greenhouse gas concentrations should perturb the Earth's radiation balance to some extent. But it is much less certain whether we will recognize this perturbation.

The uncertainty arises partly from the complex ways in which the atmosphere's hydrologic cycle acts to redistribute heat. Today I would like to emphasize only the roles of water vapor and clouds. The most fundamental function that weather systems perform is the removal of excess heat, both horizontally and vertically. Water, which is nature's air conditioner, is a critical part of this process. Air currents are continually moving heat away from the warm regions to the cooler regions. These winds evaporate water from the Earth's surface, cooling the surface an average of 55 degrees Fahrenheit, compared to a hypothetical Earth where evaporation and wind do not occur. This heat is carried into the upper troposphere by clouds where it warms the air by an average of 85 degrees Fahrenheit.

This means that moist, convective processes change the atmospheric temperature profile by 140 degrees Fahrenheit between the surface and an altitude of 10 kilometers. Thus, the temperature of the surface of the Earth is governed much more by evaporation and convection than by radiation balance. And radiation balance is the central theme of global warming theory. Therefore, how general circulation models, or GCMs, handle these moist processes is of extreme importance to global warming predictions.

Recently, a number of researchers have considered the role that the small amount of water vapor in the free troposphere has in regulating the average temperature of the Earth. And, in this view graph, that would be that large area of clear air where the air slowly sinks.

The Earth's natural greenhouse effect is dominated by water vapor, not carbon dioxide. In fact, if all the atmosphere's carbon dioxide were removed, we would still have over 98 percent of the Earth's greenhouse effects. For instance, new satellite measurements reveal extreme dryness in the subtropical high pressure zones which are vast regions of sinking cloud-free air. These dry regions act as radiative exhaust ports losing a maximum amount of heat through infrared radiation to outer space. Small changes in the vapor content of these zones can have a large impact on the Earth's ability to cool itself.

But what controls the humidity of these dry zones, these radiative exhaust ports? Their humidity source is the cloud material flowing out of rain systems which are the little dots in the tropics. You can see scattered rain systems and also mid-latitude low pressure areas provide a moisture source as well. Any cloud water that forms in these areas that does not fall out as precipitation will humidify the air.

Unfortunately, and this is a key point, we don't even have a very good understanding of what controls the proportion of cloud water that evaporates and humidifies these dry areas, let alone translate that understanding into a GCM. So, amazingly, what happens to tiny droplets within clouds ends up determining whether the Earth has a cool, dry climate, or a warm, moist climate.

Current GCMs, water vapor, act to double the warming due to CO2 concentrations, but it is not at all clear that this should be the case. Therefore, it is my contention that GCMs probably do not yet contain the cloud micro-physical processes necessary to determine how water vapor in the free troposphere will react to increasing greenhouse gas concentrations. Therefore, I believe, there is still little confidence we can place in global warming predictions for the GCMs. I do expect, however, that some existing satellite data, and especially data coming from new satellites, for instance NASA's Earth observing system a.m. and p.m. satellites, will be providing new measurements of cloud water vapor and radiation processes and will lead to improvements in GCMs. This will allow more confident predictions of global warming in the future.

Mr. Chairman, this concludes my verbal testimony.

[The prepared statement and attachments of Mr. Spencer follow:]

Statement Concerning the Role of Water Vapor Feedback in Global Warming

Roy W. Spencer

Senior Scientist for Climate Studies
NASA Marshall Space Flight Center
Huntsville, Alabama

Presented to the House Science Committee
Subcommittee on Energy and the Environment

7 October 1997

I would like to thank the members of the Subcommittee for the opportunity to review the results of our recent research on global warming.


Because the atmosphere is so complex in its behavior, the science of global warming is complex as well. Probably all climate scientists will agree that anthropogenic greenhouse gas increases in the atmosphere should perturb the Earth's radiative energy balance to some extent. But it is much less certain whether we will recognize the effects of this perturbation. I contend that the physics contained in current general circulation models (GCM's) are still insufficient to have much confidence in their predicted magnitude of global warming.

There are several reasons for this uncertainty, some of which include: 1) the radiative perturbation due to an anthropogenic doubling of carbon dioxide is small, about 1% of the Earth's natural cooling rate; 2) naturally occurring water vapor is a far more important greenhouse gas than is carbon dioxide, and it varies considerably in space and time; 3) the feedback effects of clouds and water vapor are still poorly understood; and 4) while the Earth as a whole is in radiative balance (incoming sunlight equaling outgoing infrared radiation, thus maintaining a fairly constant temperature) the surface is far out of radiative balance. This latter fact is due to evaporation and convection processes, which absorb excess heat from the surface and transports it to the upper troposphere. This upper tropospheric heat can be more efficiently radiated out to space since it is above most of the heat-trapping vapor. Thus, convective overturning of the atmosphere, and not radiation balance, largely determines the surface and upper tropospheric temperature distribution.

In this context, much of my team's research is designed to better understand why global tropospheric temperature measurements from satellites (Spencer and Christy, 1992) and weather balloons have cooled slightly (-0.05 deg. C/decade) in the last 19 years (Fig. 1; also see written testimony by John R. Christy, Senate Committee on Environment and Public Works, 10 July 1997), even though surface temperatures reportedly have increased (by about 0.10-0.15 deg. C/decade). This apparent discrepency has been debated recently in the scientific literature


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