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Relative Impact of Various Greenhouse Gases

Q23. You testified that the earth's greenhouse effect is dominated by water vapor. How much of the greenhouse effect can be attributed to:

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Q24. Dr. Spencer testified that “if all the atmosphere's carbon dioxide were removed, we would still have over 98 percent of the earth's greenhouse effects." Do you agree with that statement and if not, why not?

A24. This is misleading and irrelevant. The issue is not how much of the present greenhouse effect is produced by different gases, but how the greenhouse effect will change due to changes of greenhouse gases. It is the change of the greenhouse effect, not its total amplitude that is important. Water vapor concentration is controlled by the climate system, and actually amplifies climate change by increasing as climate warms. But carbon dioxide has a very long lifetime (order of 100 years), and so will remain in the atmosphere producing a different balance than the climate without this additional CO2.

Q25. How much would a doubling of carbon dioxide increase the overall greenhouse effect?

A25. The greenhouse effect with pre-industrial CO2 makes the global average climate about 59°F warmer than it would be without the greenhouse effect. Doubling CO2 would make the amplitude of the greenhouse effect equal to 62-67°F.

Deforestation

Q26. Does logging contribute to increasing CO2 concentrations or can it also reduce CO2 levels?

A26. Logging forests can be part of the greenhouse warming problem or part of the solution. The difference lies in what is done with the wood and what is done with the land after the

If the wood is used for construction, and trees are replanted on the land, then logging is part of the solution, and the process acts as a sink for carbon, taking CO2 out of the atmosphere. The carbon that was in the trees is turned into houses, tables and chairs, and the new trees take more carbon out of the atmosphere. The result is that some of the CO2 put into the atmosphere by other human activities is removed by the loggers, and not returned to the atmosphere, thereby aiding in the solution to the global warming problem.

On the other hand, if the trees are burned, and the land is turned into other uses, the carbon that was in the trees is returned to the atmosphere, and new trees do not remove it, making deforestation a source of atmospheric CO2 and part of the problem. This is generally the case in the tropics.

Is Climate Change Underway?

Q27. Did the 1995 report of the Intergovernmental Panel on Climate Change (IPCC) conclude that climate change is already underway, and if so, what specific climate change?

A27. Yes. See pp. 4-7. Future climate change will depend on how anthropogenic and natural forcings of the climate system change. Climate change will respond the net effects of all these forcings. If human inputs of greenhouse gases and aerosols continue as they have in the past, then the climate will warm in the next century to levels never before experienced by the human species at rates faster than climate has ever changed before. There may be unexpected surprises as the climate system passes certain thresholds.

HEARING OF THE SUBCOMMITTEE ON ENERGY AND ENVIRONMENT
COMMITTEE ON SCIENCE

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
Submitted to

Dr. Aristides A. Patrinos

Associate Director of Energy Research

and Director, Office of Biological and Environmental Research
U.S. Department of Energy

Climate Model Uncertainties

Q1.

Al.

Q2.

A2.

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?

Other important climate processes must be represented better in climate models. Most of the uncertainties are currently active areas of research. Three areas that are often mentioned are the description of energy and mass exchange at the ocean surface, the transport of heat in the ocean circulation, and the radiative effect of aerosol particles.

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.?

The great uncertainty associated with regional predictions of climate change has been discussed at length in the 1995 IPCC report, and the uncertainties associated with the polar regions are no exception. Details of sea ice thermodynamics and dynamics are being improved greatly in the next generation of climate models and should result in

Q3.

A3.

Q4.

A4.

Q5.

A5.

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 flux adjustments are not truly "arbitrary”, but are still ad hoc solutions to the problem of climate drift, that is the tendency of coupled-climate models to develop an equilibrium state that is slightly different from today's climate. The adjustments are used to adjust the regional exchange of energy and water at the ocean's surface so that the equilibrium state of the model resembles the real climate reference state. It should be noted that one US researcher, Dr. Warren Washington, and his group at the National Center for Atmospheric Research, have not employed flux adjustments in their past experiments. The next generation of coupled climate models currently being tested will significantly reduce or eliminate the need for flux adjustment.

Dr. Spencer testified that current GCMs parameterize certain processes, like cloud formation, rather than incorporate the physics in them. Please explain the difference between these two approaches. Which is better?

A "parameterization" might better be called a sub-model. It is a mathematical representation of the average grid-scale behavior of a physical or biological process that have time and space scales that are much smaller than the model is capable of resolving with its grid. For example, clouds are actually composed of small microscopic water and ice particles and have complex physical, chemical and radiative interactions with their environments. Cloud parameterizations do not describe every particle, but rather they predict the bulk thermodynamic and radiative effects of the cloud field as a whole. In GCMs, some small scale processes will always require parameterization, because we will never achieve infinitely small grid resolution. Process level research provides the knowledge required to develop accurate parameterizations.

Concerning GCMs, Dr. Robock testified that, “If you put more energy in than is being taken out, the climate warms." Dr. Spencer's testimony questions whether moist convective processes in GCMs are realistic enough to capture the ways in which the tropospheric temperature profile fluctuates naturally in response to the transport of heat from the surface to the upper troposphere, thus keeping the system in some sort of radiative balance. Do you agree that this is an issue requiring further investigation?

Yes. In fact, the convective and radiative properties of clouds are active areas of U.S.
Global Change Research Program research.

Impact of Developed Country Emission Reductions on Climate

Q6.

A6.

Q7.

A7.

You testified that you do not agree with the conclusion in a recent IPCC report, Implications of Proposed CO2 Emissions Limitations, that under a proposal by the Netherlands that would commit developed countries to a 2 percent reduction in emissions per year beginning in 2000, the reduction in projected warming in 2100 would be as little 0.1°C to 0.9°C. Please explain the basis for your disagreement with this analysis.

My disagreement lies in my belief that such a reduction in emissions is not feasible.

Bert Bolin, Chairman of the IPCC, recently said that "...no reasonable future reduction in Annex I countries would stabilize global emissions." Do you agree?

Yes, I agree with this statement.

Models and Regional-Scale Predictions

Q8.

A8.

Q9.

A9.

Concerning regional predictions, is there a general agreement as to the regional impacts, or are there large differences among the models, especially with regard to precipitation?

There are large differences among climate models with regard to the prediction of regional changes, especially precipitation, as was noted in the 1995 IPCC Scientific Assessment.

What is the resolution of climate models and how does it affect their ability to predict changes at a regional scale?

Models used in the 1995 Scientific Assessment had average horizontal resolutions that ranged from 200 to 500 km average horizontal resolution in the atmosphere. Models typically have coarse resolution near the equator and finer resolution near the poles. Greater horizontal resolution typically enhances the model's ability to predict regional changes, but does not guarantee better performance. We are currently developing historical data sets of regional climate variability over the last century or so to be used as tests for the new higher resolution models.

Q10. How would you rate the regional performance of global-scale models?

A10.

The regional performance of the global models used in the 1995 Scientific Assessment was less than what we require for rigorous assessments of impacts. Current research efforts are aimed at developing models that are capable of prediction at regional to sub

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