APPENDIX 2: Answers to Post-Hearing Questions Submitted by Members of the Subcommittee on Energy and Environment HEARING OF THE SUBCOMMITTEE ON ENERGY AND ENVIRONMENT U.S. HOUSE OF REPRESENTATIVES on Countdown to Kyoto-Part 1: The Science of a Global Climate Change Agreement Tuesday, October 7, 1997 Post-Hearing Questions and Answers Dr. Roy W. Spencer Senior Scientist for Climate Studies NASA Marshall Space Flight Center Global Hydrology and Climate Center Climate Model Uncertainties Q1. Al. Chapter 5 of the 1995 IPCC scientific notes that, “Clouds, the hydrological cycle and the treatment of the land surface remain the largest areas of uncertainty in the climate models." You have testified regarding convective processes and water vapor. Are there other areas of uncertainty where you think the models need to be improved? I believe that the response of sea ice to the change in anthropogenic radiative forcing is also an area of considerable uncertainty. It has been assumed that sea ice would melt, leading to a positive feedback on warming, but I and others believe it is quite possible that the feedback could be zero or even negative. The same holds true for the ice caps (Greenland and Antarctica), which would then impact the future predictions of sea level rise. Arctic Ice and GCMs Q2. A recent article in the Journal of Climate by D.S. Battisti and others suggests that current climate models do not represent sea ice in the Arctic regions very well, citing the variability in Arctic sea ice the authors say is not captured adequately in General Circulation Models (GCMs). As GCMs predict the greatest warming will occur over the polar latitudes in winter, how much confidence can we place in these predictions in light of the research by Battisti et al.? Flux Adjustments in GCMs Q3. A3. It appears that one problem with GCMs is the widespread use of flux adjustments— what laymen would call “fudge factors”—to make the models comport with reality. In a recent article in Science, Robert Kerr makes the observation that, “Climate modelers have been 'cheating' for so long it's almost become respectable." Mr. Kerr goes on to say that this a practice most researchers do not like. Would you explain what these arbitrary adjustments are and why they are necessary? The adjustments are necessary because the physics in the models are not sufficiently accurate to get the correct transfer of energy between the ocean and atmosphere. I believe that forecasts of global warming from models that use flux adjustments are suspect. The fact that adjustments must be made in the first place tells us that we don't know how the energy balance at the ocean surface will change with increasing CO2, since we don't even know why it is what it is today. Parameterization in GCMs Q4. You mentioned that current GCMs parameterize certain processes, like cloud formation, rather that incorporate the physics in them. Please explain the difference between these two approaches. Which is better? A4. The spatial resolution of the models is too coarse to include explicit physical equations that describe certain small-scale processes, such as clouds. To get around this problem, "parameterizations" are included in the model in which the effects of clouds are put in terms of the larger scale variables that the model can resolve. This requires some knowledge of what these relationships are, either from observations (often gleaned from field experiments in a restricted region of the Earth, or from running models (e.g. cloudresolving models) in which the explicit physical processes controlling cloud formation and dissipation are included. Explicit treatment should always be a more accurate approach than parameterization, but current computer speed limitations restricts its use in climate modeling. Aerosols in GCMs Q5. A5. Do you agree with the way aerosols have been accounted for in current GCMs, and if not, please explain the basis for your disagreement? I can only repeat what I have seen from recent scientific research, which seems to indicate that the direct radiative cooling effects of aerosols now appears to not be the explanation why we have not seen more significant global warming in recent decades. Conservation of Energy in GCMs Q6. A6. Concerning GCMs, Dr. Robock testified that, “The models conserve energy, they conserve mass, and they conserve water. They do represent the basic physics of the system. If you put more energy in than is being taken out, the climate warms." Do you agree with this assessment, and if not, why not? The models certainly do what Dr. Robock said, but they can still give completely wrong forecasts because so many more things are important to predicting the magnitude of global warming. What Dr. Robock said is only a statement of the conservation of mass and energy. The real issue is whether the feedbacks in the model are correct, and this is largely what the argument is about, the feedbacks due to clouds, water vapor, sea ice, snow cover, vegetation, etc. Human Influence on Global Climate Q7. In response to a question regarding whether the evidence for human-induced climate change was stronger, weaker, or unchanged since the 1995 IPCC, you referred to the three levels of hedging in the statement, “The balance of evidence suggests a discernible human influence on global climate." Q7.1. Please identify and comment on these three levels. A7.1. The three hedging terms are "balance," "suggests," and "discernible." When combined, the sentence literally means that there is a great deal of uncertainty in the attribution of any human influence on global climate. Q7.2. Do you agree with this IPCC statement and if not, why not? A7.2. From an observational point of view, I mostly disagree. I believe that natural influences could also explain recent warming, without invoking mankind as the cause, and that we don't understand the natural fluctuations well enough to know what portion of climate variability is due to mankind. From a theoretical perspective, however, I would agree with the statement. We know that mankind has increased the concentrations of greenhouse gases in the atmosphere, and these have some radiative effect. But then the question is, “so what?" The climate system is always changing anyway, even without our influence, and that change is so large as to mostly or completely mask the anthropogenic influence. Climate Data and Observations Q8. A8. 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? I believe that there is still considerable uncertainty in this warming trend deduced from surface measurements. I believe that the urban heat island influence has not been completely removed, and I don't believe it ever will be. This is because even rural thermometer sites can have spurious warming due to the addition of an outbuilding, or a sidewalk, etc. We know that these are real effects on the micro-climate around thermometer sites. Of course, the fact that the record isn't really "global" is also a factor in this uncertainty. For instance, the spatial coverage of the Earth by thermometers was only about 5% in the 19th century. Extreme Weather Events Q9. A9. 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? I agree with the statement. Q10. Can science directly link any one particular weather event-such as the Red River Flood-to global warming? A10. Definitely not. Role of Aerosols Q11. It has been suggested that the lack of observed warming over the past few decades has been due to the influence of aerosols, which have negated the effects of greenhouse gas increases. Would you agree with this contention or do you think the convective processes you mentioned provided a negative feedback? All. In combination with my answer to question #5 (above), I would say there is still a very real possibility that the lack of warming is due to some combination of cloud and water vapor feedbacks to the increasing greenhouse gases. Specifically, these feedbacks might be near zero instead of significantly positive, as most climate models predict. |