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Q11. Just recently, the IPCC released a report, IPCC Regional Impacts Special Report, that assessed the “vulnerability of natural and social systems of major regions of the world to climate change." Despite the caveats the report contains that the analysis does not contain “predictions that the climate will change by specific magnitudes in particular regions or countries,” the impression with the general public is that these are likely results of increasing CO2 concentrations. Are predictions of regional impacts scientifically defensible at present?

All. Users of the report mentioned above should be careful in keeping the conclusions within the proper bounds and context provided by the caveats. Some general aspects of regional prediction are defensible, such as the greater warming predicted over interior continents than over oceans. Nevertheless, the 1995 Scientific Assessment outlines the uncertainties of regional prediction in great detail.

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 that 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?

A12. Not necessarily. However, it is true that while over 2,500 scientists participated in the 1995 Second Assessment Report, the chapter titled “Detection of Climate Change and Attribution of Causes" was written by a lead author with three additional co-authors. Contributions from 32 other scientists were used in the preparation of the chapter. The four authors were responsible for the conclusions of the chapter, which were reviewed and commented on extensively before being revised for final publication. The conclusions in the Summary For Policymakers were agreed to by representatives of the participating IPCC countries and the Lead Authors for each chapter in the three volume assessment.

Theoretical Limits of the Predictability of Global Climate

Q13. Are there theoretical limits on the predictability of global climate? Please discuss. A13. The climate system is a non-linear dynamical system and as such can be classified as "chaotic", meaning that the ability to predict its future state based on its initial condition is limited. From a theoretical standpoint, there may be some measure of predictability found in the component with the longest time characteristic timescale. Because the global thermohaline circulation operates on timescales of hundreds to thousands of years, there is the potential for some measure of predictability in the climate system over these long periods. Realizing that potential may be difficult to impossible. The recent successes in predicting the El Niño/southern oscillation phenomenon has encouraged the identification of other coupled-atmosphere ocean processes which may be predictable several decades in advance. Research to date has not shown that we are theoretically unable to achieve some measure of predictability of several hundred years or more.

1995 IPCC Report and Extreme Weather Events

Q14. 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?

A14. While there is some indication of an intensifying hydrological cycle over recent decades, leading to more severe precipitation events, there are insufficient data to make any firm conclusions about a global trend in either increasing or decreasing numbers of extreme events over the twentieth century. Assembling and analyzing the data sets necessary to examine recent climate trends, including extreme events, is a high priority research activity.

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?

A15. Current global climate models simply lack the resolution and the detailed parameterizations required to simulate tropical storms. Additionally, the conditions which lead to more intense or frequent tropical storms are not well known.

"Little Ice Age” and Climate Models

Q16. From about 1550 to 1850, the world experienced the “Little Ice Age.”

A16.

16.1. How do climate models incorporate the emergence of the globe from this climatic period?

16.2. Are current GCMs able to reproduce this period?

It is not clear that the phenomenon known as the "Little Ice Age”, was either continuous in time or global in extent. The term was most likely developed because of the observed advance of Alpine glaciers in much of Europe during this time period. Attempts to model the period globally is frustrating because of the lack of global data needed to compare against the simulations. It is estimated that the global average temperature variation over the last 500 years is approximately 1.0°C. Tests of models are being developed to simulate the climate of the past 100 to 150 years, the period for which there are better observational data sets that can be used for model comparison.

Role of Aerosols

Q17. 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. It has also been 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.

A17. The regional direct effects of sulfate aerosol particles, ie their tendency to reflect sunlight and therefore act as a cooling influence, has been simulated by several modeling groups. Inclusion of this process appears to make the model simulations much more realistic when compared with data over the last several decades. When averaged over the globe, the direct cooling from sulfate aerosols compensates for approximately 1/4 of the warming attributed to greenhouse gas increases. More study is needed to reduce the uncertainty related to sulfate aerosols. It is possible that additional cooling may occur from the secondary effects of sulfate aerosols acting as cloud condensation nuclei, where the aerosol particles change the radiative properties of clouds. Soot particles may contribute slightly to global warming, but the contribution from this warming is about 1/10 of that from the greenhouse gases.

Q18. 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?

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Solar Activity and Climate

Q19. A September 26, 1997 article by Richard Willson in Science points to a strong causal link between changes in "total solar irradiance" (TSI), the radiative energy received by the Earth from the sun, and climate variability. A number of scientific articles have noted the "direct association between solar magnetic activity and climate." Historic records have shown that a reduction in solar magnetic activity between 1650-1715 may have been a “contributing factor" to the Little Ice Age. Willson's September article indicates that solar magnetic activity has increased in recent decades, and concludes that this increase could raise global temperatures.

A19.

Q19.1. Could such changes in solar activity have contributed to measured increases in global temperatures over the last decade?

Q19.2. Do current climate models take predicted changes in solar activity into account?

The variability of solar output was explicitly considered in the 1995 IPCC Scientific Assessment. Increases in solar output since 1850 may have produced a slight warming, but not nearly enough to account for the observed warming. Because of the difficulty in separating internal versus external sources of variability over periods as short as a decade, we would be reluctant to draw any conclusions about the relationship between the small changes in solar output and the slight temperature changes over the last ten years. Some newer models are including variable solar forcing, but models have not traditionally accounted for changes in solar output.

Historical Temperature and CO2 Data

Q20. 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

Q20.1. Given the above, is it true that for millennia, there has been a clear correlation between CO2 levels and the global temperature record?

Q20.2. 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?

Q20.3. What do your believe are the reasons for these apparent contradictions to the greenhouse theory?

Q20.4. Do current climate models account for such discrepancies?

Q20.5. 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?

A20. Global temperatures over these very long timescales are influenced by many factors, including sun-earth geometry, atmospheric composition (volcanic dust, greenhouse gases, ozone, etc), ocean circulation, thickness and extent of land and sea ice, land surface changes and other factors. Given that the climate is a non-linear dynamical system, close correlations between global temperature and any one of these factors over such long time periods would be surprising. Nevertheless, there appears to be some positive correlation between greenhouse gas concentrations and global temperatures over very long time periods. The climate models that are used for millennial timescale studies, called paleoclimate models, are very different from those used to study the effects of increasing greenhouse gas concentrations over periods of several hundred years. Although the governing equations for the atmosphere and ocean circulations are similar, the paleoclimate models lack sufficient resolution or sophistication in their parameterizations to be useful for detailed decadal to century scale simulations of climate variability and climate change. Conversely, the more detailed models are too computationally intensive to perform the long simulations required for paleoclimate studies over tens and hundreds of millennia. A strong effort is being made by the research community to simulate the details of climate variability over the last several hundred years to gain confidence in the ability of these models to project possible future climate changes.

Impact of Various Greenhouse Gases

Q21. Dr. Spencer testified that the Earth's greenhouse effect is dominated by water vapor. How much of the greenhouse effect can be attributed to:

Q21.1 water vapor?

Q21.2 carbon dioxide?

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