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radiation feedback, ocean circulation, the hydrologic cycle, atmospheric chemistry, and many other physical, chemical, and biogeochemical processes influence the functioning of the global Earth system.
4. Modeling the Past, Present, and Future Behavior of the Global System: Putting together all of the information on how the system functions and how processes interact can only be done using quantitative simulation models. The USGCRP supports a range of efforts to look at different time scales, different aspects of global change, and different components of the global system.
5. Estimating the Consequences of Global Change: Change is a natural feature of our world. The important issue is what the consequences of the change will be for societally important systems, such as agriculture, water resources, forests and other ecosystems, health, commerce, and industry.
6. Methods for Analyzing the implications and for Assisting Decision Makers: To support decision making in private and public settings, research is conducted that develops and tests tools that can provide an integrated perspective of change and its consequences.
Global Change Research Budget: For this hearing, you have asked us to discuss primarily the third and fourth streams of research. These are very important parts of the overall effort, but you can see that they are by no means our entire program. To provide a funding perspective, in FY 1995, agency research that focused directly on USGCRP objectives totaled about $1.8 billion. Of this amount, approximately 60% was devoted to observations and data management, about 30% to process studies, about 4% to global change modeling (with 3% supporting long-term climate modeling), and the other 6% divided between studies of consequences and the development and testing of tools for analyzing implications and decision making. The FY 1996 program of research and requested budget is described in detail in "Our Changing Planet", a document that is submitted to the Congress as a supplement to the President's
FY 1996 Budget A copy of "Our Changing Planet" for FY 1996 is attached to this testimony.
Thus, while modeling and impact studies garner significant attention, they are a relatively modest component of the overall budget. They are particularly important, however, because they are the aspects of the program where the many other parts are tied together in ways that become meaningful for analysts and decision makers.
Modeling Climate Change
Why Modeling is Vital: Attempting to understand the behavior of the Earth system and to predict and project its behavior, including its climate and the consequences of climate change, is one of the most challenging scientific problems. Spatial scales range from local to global, time scales from minutes to millennia, and processes include physical, chemical, and biological. Without the aid of computer-based modeling systems, one cannot keep track of the many important and complex interactions that govern the behavior of the planet. It is not possible to construct even a realistic physical model of the Earth system in a laboratory and to experiment with it much less a full chemical and biological model. Furthermore, it is not possible to apply in a straightforward way what has happened in the past as a means for predicting the future because of the uniqueness of human influences that now appear to be intermixed with natural processes. While all of these approaches can help to improve understanding, the only viable approach is the use of comprehensive, computer-based, models of the global system that incorporate as much knowledge as is possible of how the system works. Such models have come to be called global climate models, Earth system models, or general circulation models (GCMs), depending to some extent on what set of processes they include and how they are used. To a great extent, they represent the integrated understanding of the dynamics of the Earth system. Attached to this written testimony is a report on Earth
The USGCRP has submitted annually an issue of "Our Changing Planet", as a supplement to the President's budget submission to the Congress. These program and budget documents have accompanied every budget submission since FY 1990.
System Modeling Activities in the United States that was prepared by the coordination office of the USGCRP earlier this year.
Model Structure: Earth system models consist of reasonably comprehensive, but still limited, sets of mathematical equations that represent the state of scientific understanding of winds and air pressure, ocean currents and eddies, temperature and salinity, water vapor and clouds, solar and infrared radiation, precipitation and evaporation, snow cover and runoff, atmospheric chemistry, biogeochemical cycles, ecological processes, and many other important factors. The models are global, including treatment of the oceans, the atmosphere, the land surface, and sea ice and snow cover. Although the models have grids the size of states like Wyoming and Utah, they are able to resolve conditions only on scales of roughly one-third to one-half of the continental U.S. and over times of decades to a century. To do better requires finer spatial resolution and improved representations of processes, both of which require increased computational capabilities. While the DOE's Computer Hardware, Advanced Mathematics, and Model Physics (CHAMMP) program is helping all agencies take advantage of the most advanced parallel computers and enhanced supercomputer capabilities at the National Center for Atmospheric Research (NCAR) are facilitating the operation of larger, more complex models, tradeoffs still must be made as researchers work to most effectively address particular aspects of the problem. The GAO report entitled "Global Warming: Limitations of General Circulation Models and Costs of Modeling Efforts" identifies a number of these trade-offs, all of which are being worked on as indicated in the SGCR response letter that was included in their report. Attached to this testimony is a copy of the letter to GAO that provides some perspective on the strengths of the models that do exist and a summary of how the USGCRP is addressing their limitations.
Testing Models: In spite of their limitations, these models are quite capable of representing many aspects of Earth system behavior. Developing a sense of how much confidence to place in these models is an important, but very challenging, aspect of the USGCRP research effort. How processes such as infrared radiation are represented in the models is being tested both in the laboratory and in field
experiments. Similarly, how eddies mix heat downward from the surface into the upper ocean and how wind transports and precipitates out water vapor are being tested in major field programs. There are many processes to be examined and the major USGCRP agencies all contribute to these efforts in a coordinated manner. One set of investigations supported by the CHAMMP program has been the comparison of different models in order to evaluate their ability to simulate current climate conditions at different scales.
Another way to test the models is to determine how well they simulate past and present climate conditions. Research programs are underway to examine how well models simulate conditions drawn from recent climate fluctuations to conditions from the distant past. What is found is that, to a quite reasonable degree, climate models can simulate climate change over the seasons, the response to volcanic eruptions and El Nino warmings, and the relatively stable climate of the last 10,000 years. Models can also simulate some aspects of the very cold climates of the glacial periods and the warmer-than-present climates of the distant past (e.g., the Cretaceous period, which ended 65 million years ago when dinosaurs roamed the Earth). The models generally do best at simulating large-scale rather than small-scale features (because they do not yet represent regional details) and temperature rather than precipitation (because cloud processes generally operate at smaller spatial and temporal scales).
In using these global climate models to provide projections of future climate over the next several decades, the models are provided input scenarios on what is projected to happen to emissions of greenhouse gases, aerosols (small particles), and other human activities. The models then use these scenarios to estimate how the climate system will be affected if emission changes occur as projected. It is important to realize that the ranges of estimates usually reported in publications often combine the effects of uncertainties in the emission scenarios with the uncertainties in our representation of the climate system to generate a single range of projected change in temperature. Looking separately at these two factors, the uncertainties in the independent projections of population, technology, and other related issues are an important cause of the apparent overall uncertainty.
Agency Responsibilities: Within the USGCRP, five agencies contribute to advancing the state of global modeling. The GAO report includes information developed with the USGCRP agencies describing their areas of emphasis in modeling climate change. Examples of areas of emphasis are:
1. Department of Energy: DOE's Atmospheric Model Intercomparison Project is working with the various national and international modeling groups on simulation of the period since 1978. Other programs focus on use of massively parallel computers, the global carbon cycle, and the effects of carbon dioxide on climate.
2. Department of Commerce: In addition to significant modeling support for seasonal to interannual climate fluctuations, NOAA supports ocean-atmosphere modeling to simulate climate fluctuations from earlier this century and natural variations over longer periods, climate change due to greenhouse gases, and comparison of observed climate change to model simulations.
3. National Science Foundation: NSF supports research to simulate climates of the past, present, and future and more generally of the dynamics of the system. NSF also support supercomputer facilities used for multi-agency activities.
4. National Aeronautics and Space Administration: NASA focuses its modeling most intensely on assembling satellite data for use in developing and evaluating model behavior and in understanding the climate's response to various types of natural and human-induced forcings.
5. Environmental Protection Agency: EPA emphasizes the inclusion of ecosystems and biogeochemistry in model simulations.
Together, these agencies support an interlocking and complementary effort that provides both some focusing of activities and the diversity needed to ensure that important shortcomings are not overlooked. Attached to this testimony is a statement prepared by the coordination office of the USGCRP earlier this year that describes agency programs in global climate change modeling in greater detail.