Chapter 2. Highlights Of Recent And Current Research
The USGCRP Focus: Four Key Global Change Issues
The United States, through the U.S. Global Change Research Program, supports research needed to characterize and understand global environmental change and to provide answers to important questions about the Earth system, how it is changing, and the implications of global change for society and the natural systems on which society depends.
The underlying premise of the USGCRP is that the development of an appropriate relationship between human society and the global environment is inextricably linked to an improved understanding of the systems that are undergoing change in response to natural and human-influenced processes.
In response to the development of scientific understanding and research capabilities, the USGCRP is focusing research efforts on four areas of Earth system science that are of significant scientific and practical importance:
- Seasonal to Interannual Climate Variability, with the goal of obtaining a predictive understanding and the skills to produce forecasts of short-term climate fluctuations and to apply these predictions to problems of social and economic development in the United States and abroad.
- Climate Change over Decades to Centuries, with the goal of understanding, predicting, and assessing changes in the climate and the global environment that will result from the influences of projected changes in population, energy use, land cover, and other natural and human-induced factors, and providing the scientific information needed by society to address these changes.
- Changes in Ozone, UV Radiation, and Atmospheric Chemistry, with the goal of understanding and characterizing the chemical changes in the global atmosphere and their consequences for human well-being.
- Changes in Land Cover and in Terrestrial and Aquatic Ecosystems, with the goal of providing a stronger scientific basis for understanding, predicting, assessing, and responding to the causes and consequences of changes in terrestrial and aquatic ecosystems resulting from human-induced and natural influences.
Progress toward the Seasonal to Interannual Climate Variability  goal will provide improved predictions that can, among other direct benefits, help farmers maintain their agricultural productivity in spite of extreme climatic events such as droughts and floods; help water resource managers to ensure reliable water deliveries, limit flood damage, and maintain optimal reservoir levels; help in planning fishery harvests; and help foresters allocate resources effectively to safeguard forests (and the public) from major fires during droughts.
In FY98 and over the next several years, the USGCRP will build on its initial successes and support research activities geared to achieve the following objectives:
- Improve skills in predicting climate fluctuation, particularly over the United States
- Monitor the tropical Pacific Ocean in order to better determine its influence on climate, and to improve predictions
- Map global precipitation and its relationship to climate fluctuations
- Incorporate field data into models in order to improve forecasts of climate variability
- Assess human vulnerability to climate variations and identify options for adaptation based on improved information from predictions
- Establish a network of research centers to improve forecast model development and diagnostics, and the application of predictive information to socio-economic planning processes.
Progress toward the Climate Change over Decades to Centuries  goal is providing information needed by decisionmakers considering adaptive or mitigative responses to the projected changes in climate and the associated environmental and societal impacts. The information will also assist planners and managers with responsibilities for the design of infrastructure and other major facilities, sustained management of natural resource-based systems, and long-term planning in the financial sector.
In FY98 and over the next several years, the USGCRP will continue to address significant uncertainties through support for research activities oriented toward the following key objectives:
- Quantify the natural and human-induced factors that change atmospheric composition and radiation
- Characterize natural climate variability and the factors contributing to decadal and longer period climate fluctuations
- Improve quantitative representations of climate system mechanisms and feedback processes
- Improve scenario-driven predictions of climate change and identification of the human-induced component in the recent climate record
- Develop improved measures of the sensitivity, vulnerability, and adaptability of natural systems and project the consequences of climate change and long-term variations of the climate
- Develop improved measures of the sensitivity, vulnerability, and adaptability of socio-economic systems, and project the societal implications of climate change and long-term natural variability.
Progress toward the Changes in Ozone, UV Radiation, and Atmospheric Chemistry  goal will provide information to assist policymakers in protecting human health, preserving the cleansing and shielding qualities of the atmosphere, and ensuring that new chemical compounds released into the atmosphere do not lead to adverse consequences from changes in atmospheric composition.
The USGCRP's atmospheric chemistry research has the following objectives:
- Monitor atmospheric chemical composition trends and the human-influenced emissions that cause them
- Understand the stratospheric ozone variations during the coming most-vulnerable decade
- Monitor changes in surface UV radiation, and quantify exposure and consequences to the biosphere and human health
- Develop a predictive understanding of the chemistry of the global troposphere
- Characterize the radiative links between atmospheric chemistry and climate change
- Assess the scientific understanding of the future of the ozone layer and of the role of human-influenced chemistry in the radiative forcing of climate change.
Progress toward the Changes in Land Cover and in Terrestrial and Aquatic Ecosystems  goal will provide a stronger scientific basis for developing environmental and natural resource practices that are environmentally sound and practical, and that will ensure ecosystems can be managed to yield sustainable benefits to humankind.
Achieving the goal of research on changes in land cover and in terrestrial and aquatic ecosystems will require meeting several key objectives:
- Document the current patterns and past changes in global land cover
- Understand natural and human-induced influences that lead to changes in land cover, land use, coastal alterations, and terrestrial and aquatic ecosystems
- Predict the extent and consequences of changes in land-cover, land-use, and ecosystem processes, especially as they relate to the sustainability of natural resources and economic development
- Quantify exchanges of trace gases between the atmosphere and the terrestrial biosphere, with particular emphasis on the processes controlling carbon sources and sinks
- Observe and document the current patterns and past changes in chemical, physical, and biological activity in the oceans, especially those that are relevant to understanding the exchange of carbon dioxide with the atmosphere
- Understand and analyze the chemical, physical, and biological processes that regulate ocean uptake and release of atmospheric carbon dioxide and that control biological productivity in the oceans, and develop the predictive capabilities needed to ensure the sustainability of marine resources.
Seasonal to Interannual Climate Variability
USGCRP-sponsored research continues to achieve results that are directed toward better understanding seasonal to interannual climate variability.
Improved Prediction of El Niño Events
A number of forecasting methods based on numerical models successfully predicted the end of the prolonged El Niño conditions of 1991-95 and their replacement by colder-than-normal conditions in the eastern Pacific in 1996. This change contributed to the drought in the southwestern United States, then the heavy winter precipitation in the West. Predictions of year-to-year climate fluctuation are now being made with longer lead times than previously -- more than a year in some cases.
Additionally, studies have been initiated to determine why the 1990s have experienced prolonged multi-year El Niño conditions, in contrast to the mostly single-year events of the 1970s and 1980s. Circumstances such as these are causing scientists to look into the modulation of El Niño by longer time-scale processes.
To improve predictability, a major effort is being mounted to use more complex and sophisticated numerical models to represent the complete scope of interactions between atmosphere and ocean, and to extend the models to include the interaction of the atmosphere with land surfaces, vegetation, and hydrology.
The array of observing instruments in the tropical Pacific Ocean, initiated as part of the Tropical Ocean-Global Atmosphere (TOGA) program, has been augmented by the addition of satellite remotely sensed sea-level elevation and ocean-surface stress generated by winds. These measurements permit extension of our knowledge of changing ocean conditions to the entire tropical Pacific and to higher latitudes and are providing a basis for improved predictions of El Niño occurrences.
See Figure 2
Improved Mapping of Global Precipitation Patterns
Precipitation is among the most important climate variables in socio-economic terms because it affects water management and agriculture and causes floods and droughts. The prelude to prediction is the accurate observation of precipitation patterns and analysis to relate them to other climate variables. An excellent measure of success for climate prediction on seasonal to interannual time scales will be an improved ability to predict the amount and distribution of precipitation.
The USGCRP continues to merge in situ (on site) and satellite data to produce the best possible depiction of precipitation patterns. The Tropical Rainfall Measuring Mission (TRMM), a joint U.S.-Japan satellite mission, scheduled for launch in 1997, will provide high-quality remotely sensed observations of precipitation for the entire region between 35°N and 35°S latitudes. It will also provide a basis for accurate estimates of how the rainfall associated with the El Niño and other tropical variations affects the global atmospheric circulation and generates anomalous climatic conditions in far-removed regions of the world.
Climate Variability in North America
A 5-year (October 1995 - September 2000) enhanced observing period of the GEWEX Continental-Scale International Project (GCIP) is in progress. GCIP is gathering field data and producing model outputs that will be used to develop improved regional atmospheric, hydrologic, and coupled land-atmosphere models. During the next 2 years, GCIP will focus on three important research priorities: 1) Improving the representation of cold season processes in land-surface schemes for climate models; 2) implementing studies to link Mississippi Basin precipitation patterns to larger external processes during the warm season; and 3) developing links with water resource agencies and implementing projects that apply the results of improved precipitation and soil moisture predictions to hydrologic applications.
A Pan-American Climate Studies (PACS) special study has also begun. A primary focus of PACS is improved understanding of the processes at work in the development and decay of the North American monsoon, which is an important annual event (but one that varies significantly from year to year) in Central America, Mexico, and the U.S. Southwest.
A purpose shared by both GCIP and PACS is to ascertain to what extent year-to-year variability in summer precipitation over North America is predictable. An initial phase of determining year-to-year variability in summer precipitation in North America involves completion of a thorough observational site census.
Applications of Improved El Niño Predictions
A start-up grant for an International Research Institute (IRI) for climate prediction was issued in 1996, and steps are being taken to develop international support for the initiative, which will include a multinational network of research centers and forecast information applications activities. These efforts are intended to:
- Develop and issue experimental seasonal-to-interannual climate predictions based on global and regional modeling of ocean-atmosphere-land surface processes
- Disseminate forecast guidance to nations and regions that are particularly affected by climate variability associated with El Niño
- Tailor global and regional predictions to specific local conditions and needs.
Researchers are investigating how improved predictions can be used in management decisions across a range of economic sectors. For example, a methodology for analyzing the value of El Niño forecasts for salmon fisheries management in the U.S. Pacific Northwest has been developed. Through analysis of relevant physical, biological, economic, and management considerations, options for more efficient fisheries management as a function of possible El Niño effects can be provided. Another USGCRP study has analyzed how improved climate forecasts would affect the agricultural sector nationally and how forecasts could be used to determine likely crop yields and reduce growing costs. The coupling of climate variations to the occurrence and spread of vector-borne diseases is also being examined.
Climate Change Over Decades to Centuries
A better understanding of the science of climate change is critical to determining an appropriate global mitigation and adaptation policy. Currently, the international community is grappling with the development of such a response strategy, seeking to balance mitigation and adaptation, appropriate action by all nations, and action within a time frame that is scientifically justified and politically and economically feasible.
The United Nations Framework Convention on Climate Change represented the first international policy agreement to address the climate problem. Largely based on the scientific assessments of the Intergovernmental Panel on Climate Change in its first assessment (released in 1990), the Convention was signed into law by the United States and more than 160 other countries starting in 1992. Based on improvements in our understanding of the science of climate change as reflected in the IPCC Second Assessment Report (released in 1995), the community of nations is seeking to strengthen the treaty.
USGCRP-sponsored research continues to advance understanding of climate change processes, prediction of future climate change, and assessment of its implications for society.
Climate Change Processes
Emissions of greenhouse gases continue to rise and, consequently, so do their atmospheric concentrations (with the exception of halocarbons, which are now controlled by the Montreal Protocol on ozone depletion). Halting the rise in the atmospheric carbon dioxide concentration would require significant cutbacks in emissions over the next century. Research on the carbon cycle is aimed at helping to determine rates and magnitudes of changes in the concentrations of CO2 and other greenhouse gases in the atmosphere. As one example, studies indicate that forests are taking up about one-third of the carbon dioxide emissions, especially in regions where forest regrowth is occurring, such as the mid-latitudes of the Northern Hemisphere. It is not yet clear, however, how long this might continue.
Current research, including simultaneous measurements above and below the clouds, is seeking to reconcile theoretical understanding with empirical observations of the absorption of solar radiation in cloudy skies.
New attention is also being given to the couplings among various feedback mechanisms. For example, new observations are planned in high latitudes to address the question: As temperatures rise, to what extent might the formation of low-level stratus clouds moderate the thinning and melting of sea ice in the polar regions? This is important because climate changes in the polar regions play an important role in determining the strength of the deep-ocean circulation, which in turn has a strong influence on mid-latitude climates, including those of North America and Europe.
Predictive Models of Climate Change
Research on past changes in climate is useful in considering the degree of confidence to have in model-derived predictions of climate change. All model simulations of climate changes in the geologic past suggest that the climate system is relatively sensitive to various forcings. Climate models have predicted that temperatures in tropical land areas cooled significantly during the glacial maximum of the last Ice Age, about 20,000 years ago. Recent paleoclimatic research findings are generally consistent with these model predictions.
Significantly improved computer models are becoming available to simulate the global climate and predict future change. A new high-resolution ocean model is simulating ocean currents in the Arctic realistically for the first time. This new model and an associated global ocean model are being coupled to the improved, high-resolution atmospheric model at the National Center for Atmospheric Research. These coupled models will play an important role in simulating climate changes of the recent past and the next century, by including a more complete representation of the relevant climate forcing effects.
See Figure 3
Understanding the Implications of Climate Change
New ocean models will also provide improved estimates of the potential rise in sea level due to global warming. Research suggests that rising sea level will have important effects on coastal wetlands and communities. A rising sea level will amplify the impacts of hurricane-induced storm surges, as recently experienced in the Chesapeake Bay region. Improving models of vegetation will also provide estimates of shifts in vegetation, soil moisture, and runoff, allowing more complete studies of the consequences of long-term climate change.
Ongoing development and testing of integrated climate assessment models include improving the ability of these models to simulate the impacts of climate change on society. A particular challenge is how to model the impacts of global climate change down to regional geographic scales, as well as how to model the impacts on various natural resources and sectors of the economy, including public health. An international assessment of the social dimensions of climate change is currently being completed and will provide new insights into the importance of global change for society.
Changes in Ozone, UV Radiation, and Atmospheric Chemistry
USGCRP-sponsored research continues to advance understanding of the causes, magnitude, and consequences of changes in stratospheric ozone, UV radiation, and atmospheric chemistry.
Atmospheric Trends in Ozone-Depleting Chemicals
Satellite monitoring of trends in chlorine and fluorine levels in the stratosphere has demonstrated unambiguously that emissions of the chlorofluorocarbons (CFCs) and the hydrochlorofluorocarbons (HCFCs) from human activities are responsible for the observed five-fold increase in ozone-depleting chlorine above its natural background level in the stratosphere. These measurements, which account for the chlorine mass balance to within a few percent, are essential to understanding the full suite of chlorine sources in the stratosphere.
The measurements disprove any residual speculations that increases in stratospheric chlorine could be attributable to natural sources. When combined with recent observations of the first decreases in chlorine abundances in the troposphere, these observations further strengthen confidence that international decisions to phase out CFCs under the Montreal Protocol will lead, over time, to rehabilitation of the stratospheric ozone layer.
The Ozone Depletion Link to Climate Change
Model simulations have shown that observed latitudinal patterns of lower stratospheric cooling during the last decade are consistent with those expected from observed depletion of lower stratospheric ozone. Because of the connection between ozone depletion and emissions of halocarbons from human activities, the depletion of ozone combined with its "fingerprint" on global lower stratospheric temperatures is a strong component of the "discernible human influence on global climate" reported in the recent Climate Change 1995  assessment of the Intergovernmental Panel on Climate Change.
The magnitude of the cooling induced by ozone depletion during the past decade greatly exceeds the lower stratospheric radiative cooling calculated to have resulted from the combined emissions of all of the other greenhouse gases since preindustrial times. The cooling induced by ozone depletion partially offsets the global warming of the troposphere that results from the greenhouse effect. With the anticipated rehabilitation of the ozone layer over the coming decades, this cooling offset will diminish, raising the possibility that one outcome will be a clearer unmasking of enhanced greenhouse warming.
Observed Increases in Ground-Level Ultraviolet Radiation
Satellite observations of global ozone depletion gathered with the Total Ozone Mapping Spectrometer (TOMS) instrument, combined with measured changes in clouds and aerosols, have been used to infer increases in ground-level ultraviolet (UV-B) radiation. Poleward of about 40° latitude, statistically significant increases are calculated for the period between 1979 and 1992. The largest calculated increases in ground-level UV-B occurred at higher latitudes in winter and spring, with the most important increases occurring at the shorter, more damaging wavelengths.
For example, at 45°N latitude (e.g., Portland, Oregon; Minneapolis; Montreal; southern France; northern Italy; Bosnia), springtime exposure to DNA-damaging and erythemal (sunburn-inducing) radiation is calculated to have increased by 8.6% and 5.1% per decade, respectively, for the past 2 decades. Over highly populated areas at 55°N latitude (e.g., the United Kingdom, Scandinavia, Russia), springtime increases have been even larger, and the year-round average exposure has increased by 6.8% and 4.3% per decade. These observations quantify the previously estimated increases in ground-level UV-B associated with stratospheric ozone depletion, underscoring the importance of measures taken under the Montreal Protocol to protect the ozone layer.
Effects of UV Radiation on Human Health
Since UV radiation is a human carcinogen, a primary focus of research is to discover how it initiates or promotes cancer. Scientists have recently found evidence that a particular gene stands guard against the most common skin cancer, basal cell carcinoma, and that damage to the gene leads to skin cancer. Some of the mutations in this gene can be caused by UV exposure, which is known to promote basal cell carcinoma.
Other research results have provided new and important information related to the signaling pathway of UV-B, offering an explanation for why individuals with different pigmentary characteristics have different levels of risk for developing sun-induced skin cancers. In addition, UV radiation from sunlight has been implicated in the high incidence of skin cancer found in patients receiving azathioprine for treatment of rheumatoid arthritis.
Researchers have developed a novel and uniquely sensitive technique, the Ligation-Mediated Polymerase Chain Reaction, to map UV effects and their repair rates at the DNA sequence level in human genes. Using this methodology, they have found that repair rates can vary dramatically with sequence position. Slow repair contributes significantly to the chance for mutation in a cancer-relevant gene. This new technology has provided insights that will aid in understanding the mechanism of cancer development resulting from increased exposure to UV radiation.
See Figure 4
Changes in Land Cover and in Terrestrial and Aquatic Ecosystems
USGCRP-sponsored research continues to advance understanding of the causes, magnitude, and consequences of changes in land cover and in terrestrial and aquatic ecosystems.
Terrestrial Ecosystems and the Carbon Cycle
Measurement and analysis of changes in the atmospheric concentration of oxygen and the ratio of 13C to 12C in atmospheric carbon dioxide support the hypothesis that, in the 1990s, terrestrial ecosystems of the mid-latitudes of the Northern Hemisphere have functioned as a significant "carbon sink," sequestering up to about a third of the carbon from fossil fuel emissions. Without this sink, the rate of CO2 accumulation in the atmosphere would have been even greater.
Periodic measurements are now being taken that will lead to improved estimates of the effects of year-to-year climate variability on carbon exchange between land ecosystems and the atmosphere. This information can be used to develop and test process-based ecosystem models that are important components of the larger Earth system models. These models are critical research tools in global change science and assessment.
New land-cover data for South America, Southeast Asia, and the conterminous United States, developed from Landsat products, will facilitate better estimates of rates of deforestation and of the flux of carbon to the atmosphere associated with forest clearing. The land-cover data for the conterminous United States, which have a 1-km resolution, are an important information base for resource managers working on regional-scale planning.
Ecosystem Response to Increasing Atmospheric CO2
With continued use of fossil fuels, atmospheric CO2 concentrations will continue to rise substantially over at least the next century. A long history of CO2-enhancement studies in greenhouses, open-top chambers, and other carefully controlled growing conditions has already led to substantial understanding of the basic physiological responses governing carbon fixation in high-CO2 atmospheres.
However, there are still relatively few data on how entire ecosystems respond to increases in CO2. A network of field experiments using Free Air CO2 Enrichment (FACE) technology has now been implemented to evaluate responses of terrestrial plants and ecosystems at elevated concentrations of atmospheric CO2 expected in future decades. Initial data from crop and forest experiments suggest increased growth and net carbon sequestration in perennial ecosystems when plants are grown in the field at elevated CO2 concentrations. These long-term experiments will continue to lay the scientific foundation for understanding the consequences of future emissions of CO2 from combustion of fossil fuels.
A network of stations to measure the uptake and release of CO2 will be expanded to include a representative set of native ecosystems and a variety of land-use and land-cover types. The expanded network of measurements will be coordinated with research on processes and with studies of climatic and human factors that influence terrestrial systems.
This research will be used to refine scientific understanding of the processes that determine net carbon uptake by plants and soils and to improve the accuracy of predictions of future atmospheric CO2 concentrations. The results will help to provide the scientific basis for consideration of options for stabilizing atmospheric CO2 concentrations.
Climate Change Impacts on Terrestrial Ecosystems
Large-scale ecosystem modeling efforts are making important progress. The models can be used to simulate a range of ecological responses to changes in climate and the chemical composition of the atmosphere, including changes in the distribution of terrestrial plant communities across the globe as climate changes (see data product on back cover).
Research suggests that fire in mountain regions is likely to be increased not only by global warming but also by increased climatic variability. Analysis of the Colorado Rocky Mountains Front Range demonstrates that, over the past 400 years, fire occurrence has been extremely sensitive to climatic variability.
One of the expected consequences of global warming is rising sea level. The loss of coastal wetlands in the southeastern United States has been accelerated by sea-level rise during the past 50 years. Researchers are seeking a better understanding of the implications of continued sea-level rise for a range of wetlands ecosystems:
- Forested wetlands at low elevations are among the coastal plant communities considered most vulnerable to losses due to sea-level rise. Research indicates that large-scale shifts and/or losses in wetland forest communities will occur over the next 50 years if sea-level rise continues its current amplified trajectory.
- Research indicates that, at projected levels of sea-level rise over the next century, major portions of the coastal zone of northwestern Florida will be converted from coastal salt and freshwater marsh to open water, approaching the scale of marsh loss that has been experienced in Louisiana.
See Figure 5
Recent studies in the tropical Pacific Ocean indicate that iron, which is relatively abundant in waters near land, may be the limiting nutrient in determining primary production of marine life in the blue waters of the central ocean basins. In a series of field experiments involving controlled additions of iron salts to surface waters, scientists documented dramatic plankton blooms and concomitant drawdown of other excess nutrients. These results are encouraging studies of factors controlling primary production, carbon cycling, and ocean-climate impacts elsewhere in the world ocean.
Recent modeling studies have shown that unusual physical conditions along the break in the Georges Bank shelf off the northeastern U.S. coast during the 1950s and 1960s can be traced to changes in the cold Labrador Current. Scientists are evaluating the impact of such decadal-scale climate-related events on the dynamics of planktonic animal populations, which in turn influence marine resource populations.
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