COMMITTEE ON SCIENCE U.S. HOUSE OF REPRESENTATIVES Hearing on The Road from Kyoto-Part 2: Kyoto and the Administration's Fiscal Year 1999 Budget Request Thursday, February 12, 1998 Post-Hearing Questions The Honorable John H. Gibbons Assistant to the President for Science and Technology and Director, Office of Science and Technology Policy Post-Hearing Questions Submitted by Chairman Sensenbrenner “Clear and Compelling Evidence" That Human Activities Are Causing Climate Change Q1. Al You state on page 2 of your testimony that "the scientific evidence that climate change is occurring, and that human activities are playing a significant role in causing such change, is clear and compelling." However, at a recent American Meteorological Society international meeting on Global Climate Studies in Phoenix, Arizona, David Rind and Judith Lean of NASA demonstrated that about half of the observed global warming is ascribed to solar activity. These means that only about 0.5°F of the warming experienced in the last century could be due to other causes, including human activity. Are you familiar with this research, and if so, how does the interplay of solar activity affect climate? In seeking to be even more certain that human activities are indeed affecting climate the USGCRP agencies support a number of scientists whose research focuses on attempting to better quantify the contributions of natural influences on the climate. David Rind of NASA and Judith Lean of the Naval Research Laboratory are two of these scientists and they are making important advances that What we understand their research to show is that variations in solar radiation correlate well with changes in the Earth's climate over several centuries prior to the 20th century. As to magnitudes of natural and human changes, virtually all studies show that natural factors dominated global-scale climate changes prior to the 20th century, and that human influences are apparently dominating in the second half of the 20th century, with even greater dominance predicted for the 21st century. The Rind-Lean results also suggest that solar variability did contribute to the warming during the first half of this century, with the solar effect peaking at about 0.5° F around 1940. This warming effect has not continued fully to the present (solar radiation goes both up and down over time in cycles), so that this full amount cannot be subtracted from the 1.0 to 1.3° F warming that has occurred since the mid-19th century. In summary, we believe that the solar variation studies show that the climate is indeed responsive to change in the Earth's radiation balance and that model simulations of climate changes since 1850 are improved by consideration of solar and human influences. However, it is quite clear that if the atmosphere responds to the radiation changes of the solar cycle, it will respond even more to the dramatically greater forcing from greenhouse gases. (See attached chart summarizing the IPCC's findings). Together, these results enhance our confidence in the predictions of even more significant human-induced climate change during the 21st century. Climate Change and Extreme Events Q2. Your testimony on page 4 states that, “More precipitation is likely to occur in 'extreme' downpours, where large amounts of rain fall in a short period. Some areas will be threatened by increased flooding, while others will suffer through an increased incidence of drought, as continental interiors become warmer and drier.” However, the 1995 IPCC report, The Science of Climate Change, concludes on page 336: “Except maybe for precipitation, there is little agreement between models on changes in extreme events [emphasis added]." And even concerning precipitation, it concludes: "Several models suggest an increase in the precipitation intensity, suggesting a possibility for more extreme rainfall events [emphasis added]." A2. Do you agree with these IPCC conclusions? I accept the 1995 IPCC findings as a typically cautious summary of worldwide scientific understanding based on scientific findings through early 1995. Because of the importance of potential changes in extreme events, research in this area has intensified. The increased confidence expressed in my testimony reflects the developing understanding and the emerging scientific findings. Analyses by Tom Karl of NOAA's National Climatic Data Center show that the precipitation increases we are seeing over the last century are coming primarily as high intensity, extreme events. Total rainfall has increased in the U.S. by 5-10% in the last century, and it is the rainfall events of more than 2 inches per day that have increased the most. It is well accepted that the increased energy associated with global warming will lead to more evaporation and more water vapor in the atmosphere, which will mean in turn more energy and water vapor to be converted into intense rainstorms as convection occurs. Just as summer and warm region (e.g., El Niño affected) rainstorms produce much more rainfall in shorter times than do winter and cold region storms, there is a very strong foundation for saying, as I did, that “More precipitation is likely to occur in 'extreme' downpours." Stronger downpours will also lead to increased threats of flooding. And warmer temperatures will lead to increased evaporation (so dryness and then drought) in regions where precipitation events are now infrequent and may in the future be missed by the intensified storms. Our natural hazards studies suggest we should be very concerned about the trend toward an increased frequency and intensification |