limited use in this context; human sensitivity to climate change varies significantly across regions and social groups, and so does response capacity. We can expect to see some progress in alleviating the spatial resolution problem, as regional-scale models of climate change are further developed, but we have to recognize that the scale problems are fundamental and that no quick fixes are in sight. The other problem pertains to the interface between different methodological approaches. In particular, concerted efforts are required to develop better tools for coupling approaches relying on numerical modeling with "softer" approaches using interpretative frameworks and qualitative methods. Some of these differences are too profound to be eliminated, but that does not imply that bridges cannot be built. Learning how to work more effectively across these methodological divides is essential to the further development of integrated global change research. Again, some encouraging progress is being made.

IV. OUTLOOK

There is a growing recognition in the scientific community and more broadly that: The Earth functions as a system, with properties and behaviour that are characteristic of the system as a whole. These include critical thresholds, 'switch' or 'control' points, strong nonlinearities, teleconnections, chaotic elements, and unresolvable uncertainties. Understanding components of the Earth system is critically important, but is insufficient on its own to understand the functioning of the Earth system as a whole.

• Humans are now a significant force in the Earth system, altering key process rates and absorbing the impacts of global environmental changes.

A scientific understanding of the Earth system is required to help human societies develop in ways that sustain the global life support system. The clear challenge of understanding climate variability and change and the associated consequences and feedbacks is a specific and important example of the need for a scientific understanding of the Earth as a system. It is also clear that the scientific study of the whole Earth system, taking account of its full functional and geographical cemplexity over time, requires an unprecedented effort of international collaboration. It is well beyond the scope of individual countries and regions.

The world's scientific community, working in part through the three global environmental change programmes (the International Geosphere-Biosphere Programme, the International Human Dimensions Programme on Global Environmental Change, and the World Climate Research Programme, have built a solid base for understanding the Earth system. They also have developed effective and efficient strategies for implementing global environmental change research at the international level. The challenge to IGBP, IHDP and WCRP is to build an international programme of Earth system science, driven by a common mission and common questions, employing visionary and creative scientific approaches, and based on an ever closer collaboration across disciplines, research themes, programmes, nations and regions. We need to build on our existing understanding of the Earth System and its interactive human and non-human processes through time in order to:

• improve evaluation and understanding of current and future global change; and

place on an increasingly firm scientific basis the challenge of sustaining the global environment for future human societies.

The climate system is particularly challenging since it is known that components in the system are inherently chaotic and there are central components, which affect the system in a nonlinear manner and potentially could switch the sign of critical feedbacks. The nonlinear processes include the basic dynamical response of the climate system and the interactions between the different components. These complex, nonlinear dynamics are an inherent aspect of the climate system. Amongst the important nonlinear processes are the role of clouds, the thermohaline circulation, and sea ice. There are other broad nonlinear components, the biogeochemical system and, in particular, the carbon system, the hydrological cycle, and the chemistry of the atmosphere.

Give the complexity of the climate system and the inherent multi-decadal timescale, there is a central and unavoidable need for long-term consistent data to support climate and environmental change investigations. Data from the present and recent past, credible global climate-relevant data for the last few centuries, along with lower frequency data for the last several millennia are all needed. Research observational data sets that span significant temporal and spatial scales are

needed. Such data must be adequate in temporal and spatial coverage, in parameters measured, and in precision to permit meaningful validation. We are still unfortunately short of data for the quantitative assessment of extremes on the global scale in the observed climate.

In sum, there is a need for

• More comprehensive data, contemporary, historical, and paleological, relevant to the climate system;

• Expanded process studies that more clearly elucidate the structure of fundamental components of the Earth system and the potential for changes in these central components;

• Greater effort in testing and developing increasingly comprehensive and sophisticated Earth system models;

• Increased emphasis upon producing ensemble calculations of Earth system models that yield descriptions of the likelihood of a broad range of different possibilities, and finally,

• New efforts in understanding the fundamental behaviour of large-scale nonlinear systems.

These are significant challenges, but they are not insurmountable. The challenges to understanding the Earth system including the human component are daunting, and the pressing needs are significant. However, the opportunity for progress exists, and, in fact, this opportunity simply must be realised. The issues are too important, and they will not vanish. The challenges simply must be met.

REFERENCES

Claussen, M., 1996. Variability of global biome patterns as a function of initial and boundary conditions in a climate model, Clim. Dyn., 12, 371-379, 1996.

Gordon, C.C. Cooper, C.A. Senior, H. Banks, J.M. Gregory, T.C. Johns, J.F.B. Mitchell, and R.A. Wood, 1999: The simulation of SST, sea-ice extents and ocean heat transport in a version of the Hadley Centre coupled model without flux adjustments. Accepted for publication in Clim. Dyn.

IPCC, 1996: Climate Change 1995: The Science of Climate Change. Contribution of Working Group 1 to the Second Assessment Report of the Intergovernmental Panel on Climate Change. Houghton, J.T., L.G.M. Filho, B.A. Callandar, N. Harris, A. Kattenberg, and K. Maskell (eds). Cambridge University Press, New York, 572

pp.

Kattenberg, A., F. Giorgi, H. Grassl, G.A. Meehl, J.F.B. Mitchell, R.J. Stouffer, T. Tokioka, A.J. Weaver, and T.M.L. Wigley. 1996. Climate Models-Projections of Future Climate. In: Houghton, J.T., L.G.M. Filho, B.A. Callandar, N. Harris, A. Kattenberg, and K. Maskell (eds). 1996. Climate Change 1995: The Science of Climate Change. Contribution of Working Group 1 to the Second Assessment Report of the Intergovernmental Panel on Climate Change. p. 285–357. Cambridge University Press, New York, 572 pp.

Meehl, G.A and W.M. Washington, 1995: Cloud albedo feedback and the super greenhouse effect in a global coupled GCM. Climate Dynamics, 11, 399-411.

Mitchell, J. 2000. Modelling cloud-climate feedbacks in predictions of human-induced climate change. In: Workshop on Cloud Processes and Cloud Feedbacks in Large-scale Models. World Climate Research Programme. WCRP-110; WMO/TDNo.993. Geneva.

S Randall, D., J. Curry, D. Battisti, G. Flato, R. Grumbine, S. Hakkinen, D. Martinson, R. Preller, J. Walsh, J. Weatherly, 1998: Status of and outlook for largescale modelling of atmosphere-ice-ocean interactions in the Arctic. Bulletin of the America Meteorological Society, 79, 197–219.

Stephens, G., D. Varne, S. Walker. 2000. The CLOUDSAT mission: A new dimension to space-based observations of cloud in the coming millenium. In: Workshop on Cloud Processes and Cloud Feedbacks in Large-scale Models. World Climate Research Programme. WCRP-110; WMO/TD-No.993. Geneva.

Washington, W.M., J.W. Weatherly, G.A. Meehl, A.J. Semtner Jr., T.W. Bettge, A.P. Craig, W.G. Strand Jr., J.M. Árblaster, V.B. Wayland, R. James, Y. Zhang, 1999: Parallel climate model (PCM) control and 1% per year CO2 simulations with a 2/3 degree ocean model and a 27 km dynamical sea ice model. Submitted to Clim. Dyn.

Weatherly, J.W., B.P. Briegleb, W.G. Large, J.A. Maslanik, 1998: Sea ice and polar climate in the NCAR CSM. Journal of Climate, 11, 1472-1486.

TESTIMONY SUMMARY OF BERRIEN MOORE III

SUMMARY

Many factors continue to limit our ability to detect, attribute, and understand current climate change and to project what future climate changes may be. Further effort is needed in ten broad areas:

• Arrest the decline of observational networks in many parts of the world. Unless networks are significantly improved, it may be difficult or impossible to detect climate change over large parts of the globe.

• Sustain and expand the observational foundation for climate studies by providing accurate, long-term consistent data, including implementation of a strategy for integrated global observations. Given the complexity of the climate system and the inherent multi-decadal timescale, there is a need for longterm consistent data to support climate and environmental change investigations and projections. Data from the present and recent past, climate-relevant data for the last few centuries and for the last several millennia, are all needed. There is a particular shortage of data in polar regions and data for the quantitative assessment of extremes on the global scale.

• Understand better the mechanisms and factors leading to changes in radiative forcing; in particular, improve the observations of the spatial distribution of greenhouse gases and aerosols. It is particularly important that improvements are realized in deriving concentrations from emissions of gases-particularly aerosols, and in addressing biogeochemical sequestration and cycling; specifically, in determining the spatial-temporal distribution of carbon dioxide sources and sinks, currently and in the future. Observations are needed that would decisively improve our ability to model the carbon cycle; in addition, a dense and well-calibrated network of stations for monitoring CO2 and O2 concentrations will also be required for international verification of carbon sinks. Improvements in deriving concentrations from emissions of gases and in the prediction and assessment of direct and indirect aerosol forcing will require an integrated effort involving in situ observations, satellite remote sensing, field campaigns and modeling.

• Understand and characterize the important unresolved processes and feedbacks, both physical and biogeochemical, in the climate system. Increased understanding is needed to improve prognostic capabilities generally. The interplay of observation and models will be the key for progress. The rapid forcing of a nonlinear system has a high prospect of producing surprises.

• Address more completely patterns of long-term climate variability. This topic arises both in model calculations and in the climate system. In simulations, the issue of climate drift within model calculations needs to be clarified better, in part because in compounds there is the difficulty of distinguishing signal and noise. With respect to the long-term natural variability in the climate system per se, it is important to understand this variability and to expand the emerging capability of predicting patterns of organized variability such as ENSO. This predictive capability is both a valuable test of model performance and a useful contribution in natural resource and economic management. • Explore more fully the probabilistic character of future climate states by developing multiple ensembles of model calculations. The climate system is a coupled nonlinear chaotic system, and therefore the long-term prediction of future climate states is not possible. Rather the focus must be upon the prediction of the probability distribution of the system's future possible states by the generation of ensembles of model solutions. Addressing adequately the statistical nature of climate is computationally intensive and requires the application of new methods of model diagnosis, but such statistical information is essential.

• Expand significantly the computing resources available to address the issues of global climate and environmental change. The dual requirements of using large, complex models to perform multiple transient calculations place extraordinary demands for additional computing resources. These demands are significant and they are not being met. This is limiting progress in the United States.

• Improve the integrated hierarchy of global and regional climate models with emphasis on improving the simulation of regional impacts and extreme weather events. There is the potential for increased understanding of extreme events by employing regional climate models; however, there are also chal

lenges to realizing this potential. It will require improvements in the understanding of the coupling between the major atmospheric, oceanic, and terrestrial systems, and extensive diagnostic modeling and observational studies that evaluate and improve simulative performance. A particularly important issue is the adequacy of data needed to attack the question of changes in extreme events.

• Link more formally physical climate-biogeochemical models with models of the human system and thereby provide the basis for expanded exploration of possible cause-effect-cause patterns linking human and non-human components of the Earth system. At present, human influences generally are treated only through emission scenarios that provide external forcings to the climate system. In the future more comprehensive models of human activities need to interact with the dynamics of physical, chemical, and biological subsystems through a diverse set of contributing activities, feedbacks, and responses. • Accelerate international progress in understanding climate change by strengthening the international framework that is needed to co-ordinate national and institutional efforts so that research, computational, and observational resources may be used to the greatest overall advantage. Elements of this framework exist in the international programs supported by the International Council for Science (ICSU), the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP), and the United Nations Educational Scientific and Cultural Organization (UNESCO). There is a corresponding need for strengthening the cooperation within the international research community, for building research capacity in many regions, and, as is the goal of this assessment, for effectively describing research advances in terms that are relevant to decision-making.

The challenges to understanding the Earth system, including the human component, are daunting, but these challenges simply must be met.

BIOGRAPHY FOR BERRIEN MOORE III

Berrien Moore III joined the University of New Hampshire (UNH) faculty in 1969, soon after receiving his Ph.D. in mathematics from the University of Virginia. A Professor of Systems Research, he received the University's 1993 Excellence in Research Award and was named University Distinguished Professor in 1997; there are only two such positions at UNH. He has led the Institute for the Study of Earth, Oceans and Space at UNH as Director since 1987.

He has been a visiting scientist at the International Institute of Meteorology at the University of Stockholm, the Woods Hole Oceanographic Institution, the EastWest Center in Hawaii, and a visiting senior scientist at the Laboratorie de Physique et Chemie Marines at the Universite de Paris.

Professor Moore has authored over 100 papers on the carbon cycle, global biogeochemical cycles, Global Change as well as numerous policy documents in the area of the global environment.

Professor Moore has served as a committee member of the NASA Space and Earth Science Advisory Committee, which published its report in 1986: "The Crisis in Space and Earth Science: A Time for a New Commitment." Other committees and panels on which Professor Moore has served include the NASA Advisory Council's Committee on Earth System Science, the National Academy of Sciences' Board on Global Change, the Space Science Board's Committee on Earth Science, and the Science Executive Committee for the Earth Observing System (EOS).

Professor Moore was appointed chairman in 1987 of NASA's senior science advisory panel, the Space Science and Applications Advisory Committee, and as such, was a member of the NASA Advisory Council. In May 1992, upon completion of his Chairmanship, Professor Moore was presented with NASA's highest civilian award, the NASA Distinguished Public Service Medal for outstanding service to the agency. Professor Moore has contributed actively to committees at the National Academy of Science; most recently, he served as Chairman of the Academy's Committee on International Space Programs of the Space Studies Board. This committee, in collaboration with the European Space Sciences Committee, jointly published "US-European Collaboration in Space Science." In 1999, he completed his Chairmanship of the National Academy's Committee on Global Change Research with the publication of "Global Environmental Change: Research Pathways for the Next Decade.

In January of 1998 Professor Moore assumed the Chair of the overarching Scientific Committee (SC) of the International Geosphere-Biosphere Programme (IGBP). Prior to assuming Chair, he led the IGBP Task Force on Global Analysis, Interpretation, and Modelling (GAIM) for five years. As Chair of the SC-IGBP, he serves as lead author within the Intergovernmental Panel on Climate Change (IPCC).