to a stronger land/ocean thermal gradient in winter. The circulation pattern that causes this is not consistent with GCM projections or theory regarding "greenhouse-gas-induced" climate change.

SPM 16, lines 19-20--add "...climate forcing, although it should be able to depict observed historic climate variations."

SPM 20, line 26--Will not more carbon be fixed in areas where growth is enhanced? It is unfair to discuss retreating forest stands without incorporating regions where growth will increase due to enhanced precipitation, etc. (as was documented in Chapter 3).

SPM 23, lines 5-13--The contention that there is close agreement between the MSU and modelled data is based upon two manuscripts, one which has only been submitted and another that is "in preparation." While this statement may ultimately be deemed true, it also may be determined to be false. Thus, at this time, it is merely speculation or opinion and does not merit inclusion in this document.

SPM 23, lines 14-15--This sentence implies that the authors understand climatic cause and effect. In my opinion, this document does not provide sufficient evidence that recent observed climatic conditions are beyond the range of natural variability.

Thank you very much for requesting my input. Please let me know if you have any questions regarding my review, and best of luck on your work on the next draft.

Bob Davis

STATEMENT OF DR. JOHN CHRISTY, EARTH SYSTEMS SCIENCE LABORATORY, UNIVERSITY OF ALABAMA AT HUNTSVILLE, HUNTSVILLE, ALABAMA

Dr. CHRISTY. Thank you. It's an honor to be here.

I'm here to report on a success story. That's a story about a government scientist and a university professor that actually worked together and got something done.

Dr. Roy Spencer, a NASA scientist, and I began investigating temperatures measured from satellites in 1979, to microwave sounding unit, or MSU.

These satellites were designed to provide information for daily weather forecasts and not for climate change.

No one would have thought 15 years ago that they would have had something valuable in them relative to global warming debate until we came along.

The temperature of the global atmosphere-let's go ahead and put that up.

That top fuzzy line is the global for the last 17 years and one month. It has a declining trend of minus 0.05. That's of interest because surface data sets show a rising trend, depending on which one you use, of plus 0.09 to plus 0.19, or just in the opposite direction and of greater magnitude.

We think the MSU issue is a remarkable data record, but it has lots of ups and downs, as you can see. And I'm going to skip right to the last line on the diagram here.

When you account for forces that we know about and can quantify, you end up with a global warming trend in that last line there of plus 0.09. You can see it written there. That is the trend relative to something you might want to compare with a climate model.

Now these latest results go almost with the global climate model results that show a warming rate of about 0.08 to 0.30 for the current period in our history, once air pollution or sulfate aerosols are described.

So the 0.09, as you see there, barely fits into the 0.08 to 0.30 range, just barely into it. So it's not inconsistent with that, but it's certainly not inconsistent with natural variability as well.

Now the Spencer-Christy MSU data set has been used by some as evidence that global warming is not important and that undercuts the need and urgency for programs such as MTPE.

I strongly disagree with that interpretation.

By showing that the Earth's rate of warming is slower than predicted, by earlier models and data sets, it may remove some of the urgency for greenhouse gas controls and it perhaps gives us more time to make sure we know what's going on with the system as a whole before action-or drastic action, I should say-is taken.

Now I believe that honest and open scientific debate, with precise data such as this, is really the key to making the right kind of decisions for society.

The MSU data set would not have been developed without the competitiveness and entrepreneurial spirit fostered by having sepa

rate NASA science centers and a broad research university program.

Industry should recognize that good science and good data are their allies, whether in debates on acid rain or global warming.

Now one valuable benefit of a program of Earth observations in the improvement in weather forecasts, and particularly out to two or three weeks, or even to seasonal timescales. The potential economic impact of improved long-range forecasts would be enormous. Every sector of our economy, especially energy production and consumption, agriculture, transportation, insurance, recreation, and so on, would have more value-added if they knew further information about the weather.

I want to say, too, that there's a strong and continuing program in space-based observation is what we need. It has this benefit as well.

There will be extreme climate events in the future. There's no way to get around that. Without a continuing program of research that places these climate variations in proper perspective and reports with improving confidence on their specific causes, we will be vulnerable to calls for knee-jerk remedies to combat climate change, in quotes, which will likely be unproductive and economically damaging.

We can protect ourselves from such pitfalls by improving our ability to measure what the climate is doing and determine the causes for its variations.

I'll stop right there and wait for questions.

[The prepared statement of Dr. Christy follows:]

In the 1980's, Global Warming due to the enhanced greenhouse effect came to be perceived as a serious threat to the planet's ecological and societal sustainability. This concern was based primarily on estimates of global warming and other climate changes from numerical models of the Earth's climate system. (This perception was reinforced by a few hot, dry summers in the eastern U.S. which constituted for some people the "smoking gun" of climate change.) While the development of models is critical to our future ability to examine what we may be doing to alter the climate of the Earth, many scientists acknowledge that models are still rather simple representations of the complex processes that control the Earth's climate.

The observational evidence for enhanced greenhouse global warming is also less than clearly defined. While all surface-based global temperature data sets indicated warming of 0.3 to 0.6°C since the last century, the complete source of this warming is still unknown. First, the Earth was evidently coming out of a relatively cold period in the 1800's so that warming in the past century may be part of this natural recovery. Data sparseness and reliability are somewhat suspect in the early years of the thermometer climate record and remain a concern even today when the shrinking network of stations is attempting to capture relatively small variations. Local land use changes may also have added additional warming not connected with greenhouse gases.

With this background, scientists recognized that we did not have an observing system in place with adequate means to truly monitor the health of the planet or to provide the data needed to validate and improve the models of the Earth System. One obvious limitation of information about the atmosphere was the lack of true global coverage. NASA's EOS was conceived to provide these critical data.

2. The Microwave Sounding Unit data set

I am here to report a success story - a story that involves U.S. Government scientists and managers who collaborated closely and productively with university scientists. In 1989, the EOS data were a decade or more away. So,

to test the ability of satellites to monitor the Earth, Dr. Roy Spencer, a NASA scientist, and I began investigating temperatures measured by the existing TIROS-N family of weather satellites (average life span was only four years each). These satellites were designed to provide information for daily weather forecasts, not for answering questions about global climate change.

The instrument of interest to us was the Microwave Sounding Unit (MSU), identical copies of which were flown on all of NOAA's operational polar orbiters since 1979. The MSU measures the intensity of weak microwave radiation emitted to space by oxygen in the air. The magnitude of this intensity is proportional to air temperature, so with global coverage by the satellites we could compute the true globally-averaged air temperature. Two specific layers have lent themselves to accurate measurements: 1) the lower troposphere, or the lowest 7 km of air next to the surface, and 2) the layer at 17-21 km, or lower stratosphere.

Putting together a climate record from multiple satellites involved collecting a huge volume of data and was a remarkable achievement in and of itself. It is a tribute to the current government system and the vision of scientists at the National Center for Atmospheric Research (NCAR) that those data (with little perceived market value at the time) were saved and archived. The MSU data products are now almost priceless in the global warming debate in having established a precise historical record of the Earth's temperature over the last 17 years.

It was our good fortune that my call to NCAR asking about the possibility of obtaining the MSU data came one week before a previously scheduled, major NCAR project to copy all satellite data from an old, outdated storage system to a newer one was to begin. Thus, forewarned that Spencer and I believed the MSU data were of some unique value, NCAR kindly extracted the necessary data (only 2% of the total) for us at only the marginal cost of the extraction process. This relatively "free and open" attitude concerning data availability was the key to our success in creating the MSU data set, since obtaining the data from a cost-recovering data center would have been prohibitive (the quote was over $1 million) for the speculative value of the MSU data for climate monitoring.

The computing facilities for our own massive processing task were provided by NASA's Marshall Space Flight Center, and we had the enthusiastic support of the Earth Science and Applications Division. After several months of tedious data analysis, we were able to construct various data sets with exceptional precision and continuity. As shown in Figure 1, the particular technique we eventually developed allowed the MSU data to be independently validated by two different means.

Our data sets begin with January 1979 and continue to this day. We have been fortunate that two of the four MSU channels have performed exceptionally well on each of the nine satellites that were launched at intervals of about two years. It was critical that at least one satellite in functioning condition was orbiting