Climate Data and Observations

Q10. The 1995 IPCC report, The Science of Climate Change, concludes that, on a global average, the atmospheric temperature has risen by 0.3°C to 0.6°C since the late 19th century. Please discuss quality of the data record upon which this estimate was based. Is this record reliable and does it provide adequate global coverage?

A10. I agree with the IPCC assessment of this record.

Impact of Industrial Country Emissions on Climate

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no reasonable future

Q11. Bert Bolin, Chairman of the IPCC, recently said that reduction in Annex I countries would stabilize global emissions." Do you agree?

All. I agree, if developing countries continue to grow and use energy as inefficiently as the US now does. But if Annex I countries would stabilize their emissions, and develop the technology to allow developing countries to improve their standards of living, while using energy much more efficiently, Annex I countries can set an example and lead the world to global emissions that would be drastically reduced from what would occur with no action.

I would also like to point out that it is not necessary to go all the way to stabilized emissions to have a large impact on future climate change. A large reduction in the rate of growth of emissions would be much better than no action.

IPCC Process

Q12. Dr. Spencer testified that “when the IPCC comes out and says, ‘2,500 scientist have agreed, now, that humans are responsible for climate change,' most of the scientists -besides the fact [of] not really being consulted on whether they agreed with that statement-most of them aren't even in a position to have a feeling for whether the big picture supports global warming or not." Do you agree with that statement and if not, why not?

A12. The IPCC report was reviewed extensively by the scientific community. I agree that all 2,500 scientists do not specialize in global climate change, but rather work on a smaller component of the problem. This is a complicated problem, and needs experts in many areas, including oceanography, biology, data analysis, clouds, and computer modeling. It is difficult to measure whether particular scientists "have a feeling for whether the big picture supports global warming or not." If Dr. Spencer means by this, that the scientist has training in meteorology and climate, and has considerable experience in global climate modeling and data analysis, then of the 4 panelists at our hearing, I would say that only I

Hurricane Frequency

Q13. A paper co-authored by C.W. Landsea that appeared in the journal Geophysical Research Letters in 1996 shows that there has been a downward trend in the intensity of hurricanes since 1944. Another paper co-authored by Tom Karl also shows that since the 1940s the number of hurricanes making landfall in the U.S. also has declined. Is it fair to say, based on this peer-reviewed research, that the intensity and frequency of hurricanes have gone down in the last 50 years?

A13. I have not studied this issue, but I know that we do not have good enough observations of the number or intensity of hurricanes occurring in the world for the past 50 years to make this statement. On the other hand, we also cannot say that hurricanes have been increasing. For the U.S. East and Gulf Coast, we have better data, and I have no reason to dispute Landsea or Karl. Whether the intensity and frequency of hurricanes has gone down or stayed the same, is not sufficient information to predict how they will change in the future. But there is no strong evidence that hurricanes will increase or become more intense in a greenhouse-warmed world.

Hurricanes in GCMs

Q14. You testified that global warming will result in more intense storms. While many scientists have linked increasing temperatures with increased tropical storm activity, others have reached different conclusions. For example, a study by Robert Balling and others, which appeared in Meteorology and Atmospheric Physics in 1990, concluded that "There is basically no trend of any sort in the number of hurricanes experienced... with respect to variations in temperature." Looking to the future, Lennart Bengtsson of the Max Planck Institute of Meteorology reported in the journal Tellus that, based on model simulations, a doubling of CO2 would lead to fewer hurricanes. In your view, can a valid scientific case be made that an increase in CO2 could lead to no change or even a lessening of tropical storms?

A14. In my testimony I was referring to the severity of convective storms, which might increase as the surface warms and the upper troposphere cools. I was not referring to tropical storms. As stated above, there is no strong evidence that hurricanes will increase or become more intense in a greenhouse warmed world.

Tropical Storms in GCMs

Q15. The 1995 IPCC report states: “Although some models now represent tropical storms with some realism for the present day climate, the state of science does not allow assessment of future changes.” Do you agree with this assessment and if not, why not?

Q16. Concerning extreme weather events, the 1995 IPCC Summary for Policymakers states that, "There are inadequate data to determine whether consistent global changes in climate variability or extremes have occurred over the 20th century." Do you agree with that assessment and if not, why not?

A16. Yes, I agree.

Q17. Can scientists directly link any one particular event—such as the Red River Flood— to global warming?

A17. No.

Melting of Glaciers in Glacier National Park

Q18. Can the melting of glaciers in Glacier National Park be attributed to global warming or have these glaciers been in recession before the increase in atmospheric concentrations of CO2 resulting from human activity?

A18. Certainly, climate change in any location is a response to local, not global changes. Glacier retreat can be caused by a combination of warming and precipitation reduction. As discussed above, we do not have much confidence in our ability to link local changes to global changes at this time.

Role of Aerosols

Q19. There has been a great deal of controversy concerning the impact of aerosols on the results of climate models. A recent GCM by J. Hansen and a paper in Science by S. Tett et al. indicate that the impact of sulfates is generally slight or neutral. Other research has also suggested that the impact of aerosols could be offset by carbon particles in the atmosphere, which absorb heat, from fossil fuel burning. Please discuss the uncertainties regarding our understanding of aerosols in GCMs.

A19. This answer could be 100 pages long, but I will briefly summarize. Most GCMs are just now including radiation models that can explicitly consider the effects of aerosols. Many experiments with aerosols to date have been made by just changing surface albedo as a surrogate for the radiative effects of aerosols. Much more work is needed to test a variety of aerosol types and their effects on climate. In general, however, sulfate aerosols tend to cool the surface by their direct and indirect effects, and carbon particles can either warm or cool the surface depending on the height of the aerosol cloud. The carbon particles absorb sunlight and heat the atmosphere, preventing some solar energy from reaching the surface. But they also emit more longwave radiation downward, compensating for this

Q20. Among the findings of a 1996 National Research Council report, Aerosol Radiative Forcing and Climate Change, were the following: “(1) anthropogenic aerosols reduce the amount of solar radiation reaching the Earth's surface, (2) anthropogenic aerosols provide a negative climate forcing function for large regions, (3) global models suggest that sulfate aerosols produce a direct forcing in the Northern Hemisphere of the same magnitude as that from anthropogenic greenhouse gases, but opposite in sign, and (4) there is substantial uncertainty about the magnitude and spatial distribution of the radiative forcing by aerosols.” Are these findings still pertinent?

A20. Yes, I agree with all these statements, and the most recent work strengthens these conclusions. I might point out that I first published these conclusions in 1978 (Robock, Alan, 1978: Internally and externally caused climate change. J. Atmos. Sci., 35, 11111122).

Global Warming and the Possibility of a New Ice Age

Q21. Some researchers have recently projected that global warming could lead to a new ice age.

Q21.1 Do you lend this projection any credence, and if so why?

A21.1. No.

Q21.2. Do current climate models provide any guidance of this matter? If so, what do they forecast, and if not, does this mean that there will be no more ice ages?

A21.2. Ice ages are caused by changes in the Earth's orbit over time scales of tens of thousands of years. These continue to occur, but will not affect our society for a long time to come. Human interference with the climate system as projected for the next few centuries may be quite large, so any resulting climate change will be the net effect of all changes in the boundary conditions (the forcings) of the climate system.

Temperature and CO, Record

Q22. The geologic record reveals that major changes in the atmospheric concentration of CO2 and temperatures have occurred during the earth's history. Over the last 160,000 years the Earth's average temperature has varied by as much as about 14° F, while CO2 has varied from as low as about 160 parts per million to today's figure of more than 360 parts per million. While a general correlation of CO2 and temperature seems evident in this record, a closer examination reveals a number of contradictions. For example, about 135,000 years ago, when the temperature was some 3 degrees warmer than present, atmospheric CO2 concentrations were about

20 percent less than today. In addition, over the next 20,000 years, the temperature decreased by about 14 degrees, while the CO2 levels remained high and relatively constant during that period. More recently, in the interval between about 5,000 to 9,000 years ago, there were several short-lived warm periods when temperatures exceeded current levels by 1 to 2 degrees, but CO2 levels were about 25 percent below today's levels. The greenhouse theory tells us that we should expect more warming when there is more CO2 and less warming or even cooling when there is less CO2, but it appears that none of these features of past climate can be explained by the greenhouse theory.

Q22.1. Given the above, is it true that for millennia, there has been a clear correlation between CO2 levels and the global temperature record.?

A22.1. As I discussed above, climate change is a result of the net effect of all changes in the boundary conditions (the forcings) of the climate system. The amount and seasonal distribution of sunlight was the main cause of these past climate changes, and the CO2 amount was a response of the climate system to changing sea surface temperatures. The changing CO2 amount provided a feedback on the climate system. These past changes are completely consistent with our current understanding of climate change, and in fact have been reproduced by the same climate models that predict global warming from the large projected increase in CO2 and other greenhouse gases.

Q22.2. Given the above, is it true that records of past climate going back as far as 160,000 years indicate a close correlation between the concentration of greenhouse gases in the atmosphere and global temperatures?

A22.2. There is a correlation, but this does not necessarily imply a cause and effect relationship.

Q22.3. What do your believe are the reasons for these apparent contradictions to the greenhouse theory?

A22.3. There are no apparent contradictions. See answer to 22.1 above.

Q22.4. Do current climate models account for such discrepancies?

A22.4. There are no discrepancies.. See answer to 22.1 above.

Q22.5. Can current models replicate the Earth's past climate of say the past 160,000 years, or the past 10,000 years? If so, to what accuracy, and if not, why should one have confidence in the projections of such models?

A22.5. Yes, but I have not studied this issue and cannot give you a precise answer as to