DECADAL TO CENTENNIAL CLIMATE
Working Group Participation
Eric J. Barron, Chairman
Francis P. Bretherton
William E. Easterling
Roy L. Jenne
Richard S. Lindzen
Jerry D. Mahlman
Douglas G. Martinson
Designated Federal Liaison: Michael C. MacCracken
Rapporteur: John Perry
WORKING GROUP SUMMARY
Eric J. Barron,
Eric J. Barron, Chairman
The last decade of research has demonstrated two important points. First, significant climate variability on time scales of decades to centuries has occurred in the past and will likely continue into the future. Second, the potential exists for significant changes in climate and climate variability over the next decades to centuries in response to human activities.
Substantial advances in climate understanding and prediction have occurred over the last decade:
- There have been recognition and documentation of the scope of natural variability, involving (1) remarkable records of variability and rapid change from ice cores, tree rings, and corals; and (2) determination, by means of models, that ocean-atmosphere interactions can lead to significant variability on a variety of time scales.
- Calibrated five-year Earth Radiation Budget Experiment (ERBE) observations have documented that clouds have a net global radiative cooling effect on the Earth-atmosphere system by about 15 to 20 watts per square meter. The regional cloud forcing data have contributed significantly to diagnosing deficiencies in general- circulation model (GCM) treatment of cloud radiative interactions.
- Water vapor behavior and feedback analysis has been advanced on theoretical, observational, modeling, and methodological grounds.
- Understanding the role of volcanic eruptions as a climate forcing factor has been advanced, as evidenced by our ability to measure and examine the impact of recent eruptions (Mt. Pinatubo).
- The linkage of climate models with impact models on agriculture, water resources, ecosystems, and the economy, and quantification of the positive and negative effects of climate change and variability on agricultural production and water supply, have been substantially improved.
This research, however, has also underscored the complexities and uncertainties associated with detecting and projecting the nature of future climate change. For instance, a concern for anthropogenic global change cannot be dealt with in the absence of an adequate understanding and documentation of present and future climate and its natural variability on time scales of years to centuries, as well as a quantified understanding of anthropogenic forcing itself. For anthropogenic forcing, we clearly need to determine the role of tropospheric aerosols and further elucidate of the carbon cycle.
Determination of the response to anthropogenic forcing is inseparable from understanding the natural system. This understanding ranges from solar and volcanic variability; to the feedbacks resulting from the interactions of water vapor, clouds, and radiation; to the massive heat fluxes associated with the motions of the air and oceans and the exchanges between them.
In short, changes in all the major factors that influence climate variability must be well described and their interactions understood. The evidence clearly shows that we must be able to couple the components of the Earth system, including the ocean, atmosphere, land, and ice, and describe major feedback processes in order to be able to reduce the uncertainties in describing the nature of future climate. The primary characteristics of the climate system must also be documented through consistent, long-term observations.
An understanding of both natural variability and anthropogenic global change is essential to address the wise use of resources, human health, agricultural productivity, and economic security. Improved global change predictions are central to these objectives and are key U.S. Global Change Research Program (USGCRP) research priorities. Addressing these complexities and uncertainties requires a comprehensive program. Each of the essential science elements listed below addresses uncertainties that currently hinder our ability to understand and predict future climate variability and change.
Essential Science Elements
- USGCRP must characterize and determine the changes in the significant global change forcing factors (solar, carbon dioxide, other radiatively important gases, aerosols, land cover change) by means of continuous observation. Tropospheric aerosols are a major priority that have not been adequately addressed.
- USGCRP must document global change (e.g., temperature, precipitation, ozone, air quality, ecosystems). Climate change requirements must be a part of current and future observational systems (including operational elements) and of satellite convergence efforts.
- The identification and understanding of the natural variability of climate, including the historical and paleoclimatic record, must be a product of USGCRP efforts.
- An ability to quantify the carbon cycle and its driving factors is essential for determining future atmospheric carbon dioxide levels.
- USGCRP must have the combined observations, process studies, and modeling efforts necessary to address the issue of cloud-water vaporadiation feedback, which remains the major source of uncertainty in climate change predictions.
- USGCRP efforts must be able to characterize the nature of the oceanic circulation, the surface fluxes of energy and moisture, and the ocean's natural variability.
- USGCRP must have the combined observations, process studies, and modeling efforts necessary to address land-vegetation- atmosphere interactions.
- It is essential to characterize and understand cryosphere (ice caps, sea ice, snow cover) responses to climate change.
- USGCRP must include the basic science capabilities to address the impacts of global change on ecosystems, (e.g., forests and agriculture) and on water resources.
- The critical economic, technological, and demographic trends that are affecting the ability of natural and human systems to cope with climate variability and change must be understood. These include changes in urban infrastructure, farming technologies, trade, and water use and efficiency--all of which can increase vulnerability or resilience to global change.
In reviewing the science elements above, all the major elements of the current program (e.g., Earth Observing System (EOS) measurement priorities, the National Oceanic and Atmospheric Administration (NOAA) climate research elements; the basic research components of the National Science Foundation; and the Department of Energy's ARM program) are essential. In fact, some of the elements (e.g., item 1,2,8, and 9 above) are currently not well addressed and must be enhanced. This must not occur at the expense of understanding basic features such as heat transfer by the oceans and atmosphere. There is little room for budget cuts in decade to century climate research without significant damage to critical science objectives. We, therefore, conclude that substantial budget reductions must come from other program elements, such as diverting savings from satellite convergence or increasing the efficiency of the EOS Data and Information System (EOSDIS). A multifaceted, balanced program that addresses each of these ten major science elements is essential so as not to have major gaps in our understanding that serve to limit both the utility of measurements and our predictive capability.
Issues of importance to the success of USGCRP are not restricted to addressing scientific priorities; a number of management issues, if addressed, would result in a stronger program. The field of global change research has had a history of significant progress and evolution involving integration of the essential components of research: data analysis, theory, and modeling. The maintenance and enhancement of progress demand a balanced approach. Intensive examination of existing and future observations (in situ and remote), improved theory and modeling, the maintenance of existing and future measurements and calibrated monitoring, and the inclusion of climate considerations in the design of routine observations are required to satisfy crucial needs. Satellites offer unique capacity for global coverage and monitoring, and in situ measurements offer unique capacity for validation and for addressing critical details.
Essential Programmatic Changes
- USGCRP must not be considered a collection of quasi- independent activities, although some independent efforts are necessary for creative opportunity. Nevertheless, the larger components must be managed as a set of serious scientific programs requiring continuous oversight, connectivity, and continuity across agencies; resource allocations and goals must be adjusted in light of developing knowledge and budget changes.
- A scientifically and financially balanced program is essential, with strong components spanning in situ observations, satellite observations, process studies, and integrative modeling. The present management limits such balance.
- The United States must enhance the linkages between national and international programs. However, the United States has become an untrustworthy international partner. Enhancement requires greater integration, which is difficult without stronger U.S. long-term commitment.
- USGCRP must have the flexibility to include exploratory efforts. Part of the strength of a robust program involves opportunities for innovative inquiry by individual investigators and a capacity to address new issues.