The U.S. Global Change Research Program stands at the threshold of a major transition. Over the next several years, in addition to continuing to improve our understanding of the Earth’s environment and how it is changing, the program will advance greatly our understanding of the implications of such change for society. The research successes of the last decade have laid the foundation for establishment of a global environmental change information service that will allow global change research results to be applied more effectively to national needs.

    In the early 1980s, when climate research began in earnest on a global scale, the problem of understanding the entire Earth system seemed in many ways intractable. Climate system behavior, excepting a few well-known features such as the ice ages and the annual march of the seasons, seemed chaotic. Accurate prediction of the future course of change thus appeared very unlikely. Although it was apparent that scientific research was required to increase understanding of a set of newly identified global-scale environmental changes, it was by no means clear where progress was most likely to be achieved.

    In response to this challenge, the establishment of the U.S. Global Change Research Program led to a comprehensive program of support for research across a broad range of Earth system science issues. The result has been a remarkable change in perspective. Scientists discovered the ozone hole, in part through routine surveillance; determined its spatial extent, temporal behavior, and chemical origins; and showed it was caused by human activities. Observations demonstrated a long-term, statistically significant decline in ozone amounts over most of the Earth’s lower atmosphere, much of which is attributable to changes in atmospheric chemistry associated with human activities. A rapid increase in scientific understanding supported a global consensus on steps to ameliorate the problem. Ongoing research and monitoring have shown that the emissions controls on chlorofluorocarbons (CFCs) and related molecules implemented under the Montreal Protocol on Substances That Deplete the Ozone Layer have begun to have an effect, as the concentration of chlorine-containing source gases at the Earth’s surface has begun to decrease. Field experiments, long-term global observations, and computational modeling all played key roles in advancing our scientific understanding of ozone depletion.

    As these events took place, another group of scientists began to pursue studies of El Niño, leading to equally remarkable scientific developments. These studies have shown beyond any doubt that the El Niño-Southern Oscillation process, in which the actions of the ocean and the atmosphere are closely coupled, has some degree of predictability in its behavior. The scientific community, working in the context of the USGCRP, successfully predicted the onset of the 1997-1998 El Niño and some of the resulting climate anomalies around the world. Societies made limited but significant advance preparations; in some cases economic consequences were minimized and loss of lives and property was reduced.

    Coincident with these and other research successes, a large fraction of the research community was achieving an even more visible and significant result. USGCRP-supported observations and analyses played a prominent role in demonstrating that emissions of carbon dioxide and other trace gases resulting from human activities are changing the composition of the atmosphere. Projections indicate that the changes over the next century will increase atmospheric concentrations of greenhouse gases to levels not seen in tens of millions of years — periods when the climate was substantially different than today. Observations suggest that the human-induced changes in atmospheric composition are already starting to change the climate. Careful measurements of surface temperatures around the world indicate that the global average temperature has risen substantially in the latter half of this century, compared both to observed temperatures since the 19th century and to estimated temperatures reconstructed from tree rings and other evidence back as far as a thousand years. Substantial improvements in climate models have been achieved and these models project increases over the next century in global average temperatures of from 2o to 7o F, as well as shifts in precipitation and a significant acceleration in the rate of sea-level rise.

    Observations and monitoring from space of changing land cover, along with the production and distribution of global land cover data, are providing an important foundation for efforts to make land use more sustainable. For example, satellite observations supported by the USGCRP in coordination with international projects have documented and quantified changes in tropical and subtropical land cover, such as the loss of tropical forest in Brazil. Changes in land cover and land use are occurring around the world at an increasingly rapid rate, driven largely by human activities. Research has documented that changes in land cover such as the conversion of forest to pasture in the tropics, and changes in land use such as increases in fertilizer applications to cropland worldwide, are contributing to changes in atmospheric composition and may also contribute to climate change on both regional and global scales.

    The real significance of all these scientific developments is seen most clearly when they are taken together. Several major environmental processes are now understood and there is some degree of predictability in their behaviors. A deeper appreciation of how the Earth’s oceans, atmosphere, and land surface function together as a dynamic system is being gained. Over the next decade, the causes and consequences of an entire suite of interacting large-scale environmental changes will be better understood. The future course of such changes, and the limitations of prediction, will become clearer. Scientific knowledge will improve the preservation and enhancement of environmental quality and the management of environmental change.

    Achieving this vision requires new science findings and better assessment and interpretation of scientific information. The full spectrum of public and private-sector decisionmakers also need routine, reliable, and readily understood scientific insight.

    Science has much to contribute to the management of these issues. Longstanding climate-related problems (e.g., droughts, floods, reduced agricultural production, and pest infestations) now can be anticipated to some extent. Better understanding of the complexity of changes on planet Earth, such as temperature and precipitation patterns, creates opportunities to reduce exposure and enhance resiliency in socioeconomic systems.

    Estimating in advance the magnitude of these problems or the value of opportunities to respond is extremely difficult. One thing is already clear, however — current economic measurements alone do not suffice to explain or judge the severity of such problems. The importance of some issues far outstrips any purely economic measurement. Some representative examples:
 

• Societal Costs and Impacts of the El Niño: In any given year, the effects of weather and climate result in societal costs. Climate anomalies of the past two years, most directly related to El Niño, have accounted for worldwide impacts exceeding $30 billion. Inclusion of impacts related to the recent flooding in China, which is believed to be partially attributable to the 1997-98 El Niño, could push these direct losses to $60 billion. This most recent El Niño also claimed 21,000 lives, displaced 4.5 million people, and affected 82 million acres of land through severe flood, drought, and fire. Costs from the El Niño in terms of slowed development and lost opportunities have yet to be measured, but surely involve economic losses even higher than the direct costs. Early estimates of the value of preparedness in areas such as California and Peru suggest that perhaps one-half of the likely cost in the absence of any advance warning was avoided in 1997-98. These limited successes were based on experimental predictions that can be further improved. When regional summer climate perturbations are better understood and projected, the severe impacts of events like 1998's multi-billion-dollar U.S. drought or the tenfold-more-expensive floods in China might be ameliorated -- any reduction in their impacts would be a noteworthy improvement. The knowledge of how to avert disaster through forecasting, make advance preparations, and use early warning systems effectively now appear to be within reach scientifically.

• Patterns of Change in the Frequencies of Hurricanes: Over the next decade, it will likely become known whether the recent epoch (nearly 30 years) of infrequent hurricane landfalls along the East Coast of the United States — during which time we have greatly increased our vulnerability by building in coastal regions — has been supplanted by a return to conditions similar to those of the 1930s, 1940s, and 1950s. In that event, it is much more likely that the long-feared "category 4" (132-155 mph, such as the unnamed 1947 storm that hit southeast Florida and Louisiana) or "category 5" hurricane (156+ mph, such as the 1935 Florida Keys storm) will make landfall in a densely populated area by 2010. The losses to the insurance industry from such an event, or the cumulative impact of more frequent category 2 and 3 events, could render privately funded insurance unavailable, perhaps even bankrupting a large portion of the industry. Studies of a category 4 hurricane that passed through Florida and Alabama in 1926 indicate that the same hurricane today would cause an estimated $77 billion in damage. The economic and societal value of supplying constantly improving information that could enable the industry to remain viable is still unknown. This value could be substantial; that the industry itself is investing in some research on this subject indicates its high level of concern. Such information will allow U.S. Government decisionmakers to assess more reliably whether or not to become the default insurer. Some, but not much, of the needed information is available now. Again, much more relevant information is believed to be within reach scientifically with a sufficient research effort.

 
• Issues of Fresh Water Availability: Social scientists commonly identify limited availability of fresh water, a resource many of us take for granted in the United States, as potentially one of the most pervasive crises of the coming century. Setting aside the question of whether certain countries may have gone to war over water by 2010, how will things look politically and economically in the American West? Tension between states and localities will have reached acute levels if the climate system continues to exacerbate problems such as the diminished Colorado River runoff. (The Ogallala Aquifer in the Texas High Plains offers an example of affected populations already having to adjust to changes in the water balance.) Is the West’s water supply sufficient to meet future needs? In the fastest growing areas of the West the demand for water for all uses already exceeds supply. What, then, will a knowledge of nature’s tendency to sustain or hinder development in the West ultimately be worth? Insights provided by studies of the historical impacts of climate on water and agricultural resources, and emerging from current research efforts, indicate that this problem could prove to be extremely costly. For example, under current conditions, it is estimated that droughts cost, on the average, $6 billion to $8 billion annually within the United States. Thus, advances in current understanding of these and recent multi-billion-dollar droughts (such as the 1987-1992 events in the West and the 1995-1996 event in Texas) may lead to improvements worth up to a billion dollars annually.

 
• Influences of Sources and Sinks for Carbon on the Earth’s Climate: By 2010, scientists throughout the world will be producing regional maps of large carbon sources and sinks. In all likelihood, managed terrestrial ecosystems (e.g., replanted forests) will have been shown to be an important multi-decadal sink. By 2010, the United States may well have been confirmed and shown conclusively to possess such a sink and to have the capacity to augment it, again subject to major social forces pro and con. The gradual realization by governments of the full implications of these regional maps of carbon sources and sinks cannot help but alter the terms of the debate about emission controls. If the scientific effort is integrated across ocean, land, and air and managed effectively, it can demonstrate to the world that an adequate monitoring effort is feasible and that regional mitigation and sequestration can be made a serious part of the international negotiations. This invaluable information seems well within reach of the research effort which is already organizing to do the job.

 
• The Influence of Climate Change on the Salmon Fishery: In the United States, renewal licensing of major dams constructed decades ago has become a serious issue, in part because of the ecological consequences of their presence. The USGCRP has helped to clarify the relationship of climate-related regional variations in salmon productivity on timescales of a few decades to overall observed decline in the Columbia River and other Pacific Northwest river ecosystems. Many other insights about the coupling of the Earth’s major ecological systems to climate variability and change will result from the proposed research effort. The availability and timeliness of these insights will rest very much on the kind of research program assembled. This program can provide relevant information not only about the freshwater resource on which the dams and the fish depend, but a far more complete picture of the true natural background against which the effects of the dams can be judged.

 
• Changes in Air Quality: The combination of population growth and industrialization of developing countries, notably in South and East Asia, is leading to dramatically reduced air quality in these regions on a large spatial scale. Plumes of polluted air are being transported out into previously unpolluted regions and at some times reach the coastal regions of the United States (in particular the West Coast), affecting the background concentrations of ozone and other species important for air quality in some regions. New satellite instruments for measuring tropospheric ozone will show clearly the spatial extent of these plumes and their day-to-day variation. Governments in these developing countries will begin to realize that they must take steps to control local pollution, including reduction of fossil fuel combustion, switching to less polluting fuels (e.g., from high-sulfur coal to petroleum products containing less sulfur), and importing of emissions control technologies. Such steps offer the potential to reduce greenhouse gas emissions and emissions of air pollutants at the same time. Results obtained from the USGCRP on global tropospheric chemistry will allow U.S. policymakers to understand better the sources of polluted air and the regional and global impact of these emissions and their changes.

 
• Changes in Ozone Concentrations in the Atmosphere: The Montreal Protocol will continue to lead to reductions in concentrations of some ozone-destroying gases in the atmosphere in the early part of the 21st century. Many of the "quick fixes" called for under the Protocol (e.g., reduction of methyl chloroform) already will have taken place, and halogen concentrations will have begun to decrease very slowly, based on the natural lifetimes for CFCs, which are more than 100 years for some compounds. Monitoring by the USGCRP of surface-level concentrations of CFCs, their replacements, and related halogenated hydrocarbons is helping to assess international compliance with the Protocol, and may help provide information on the regional distribution of emissions of any regulated compounds. The response of the ozone layer to these reduced levels of CFCs and related compounds is studied routinely by USGCRP agencies with a combination of ground-, balloon-, and space-based instruments. These measurements and associated modeling efforts will continue to help demonstrate whether the "replenishment" of the ozone layer is occurring, as is expected, as anthropogenically amplified stratospheric chlorine levels decrease — or, alternatively, whether other processes (such as stratospheric cooling associated with increased greenhouse gas concentrations or increasing levels of stratospheric bromine) are interfering with the expected recovery by creating conditions under which lower amounts of chlorine can still deplete stratospheric ozone.