and their influence in the coupling of the atmospheric water and energy cycles, and of the vertical transport and mixing of water vapor on scales ranging from the local boundary layer to regional weather systems. Focus for FY 2000: The USGCRP will demonstrate skill in predicting changes in water resources and soil moisture on timescales up to seasonal and annual as an integral part of the climate system. As a first step, the program will quantify evaporation, precipitation, and other hydrological processes as required to improve prediction of regional precipitation over periods of one to several months The USGCRP will demonstrate the ability to determine radiative fluxes and diabatic heating within the atmosphere and at the surface with the precision needed to predict transient climate variations and to understand natural and anthropogenically-forced climate trends. The USGCRP will combine Tropical Rainfall Measuring Mission (TRMM) measurements with rainfall measurements from other sources to set a benchmark for rainfall in the tropics. We will obtain maps of the diurnal cycle of precipitation (which cannot be obtained from sun-synchronous sensors). The insight gained from this exercise will be used to reprocess 10 years of SSM/I data for climate record. This 10year data set and ongoing TRMM measurements will be used to validate climate models as well as demonstrate the impact of rainfall in assimilation and weather forecast schemes. The USGCRP will establish a climatologically valid database of 60 months of rainfall data from various ground validation radar sites. The program will achieve 10% agreement among the various TRMM-related sensors for zonally averaged monthly rainfall accumulations. This will establish our confidence in how well tropical rainfall, a central component of the global water cycle, can be measured from space. The USGCRP will complete cloud model simulations of major storm systems in the Brazilian Amazon and at the Kwajalein atoll oceanic site for the purpose of testing latent heating estimates from TRMM. The USGCRP will assess the accuracy of remote and in-situ humidity measurements, and improve understanding of the climate consequences of water vapor radiation feedback. The program will conduct a field experiment at the DOE radiation testbed facility in Oklahoma, under joint NASA and DOE sponsorship. The USGCRP will conduct data comparison workshops, establish validation sites, and expand and improve global water vapor data sets toward the goal of quantifying and understanding the role of water vapor in meteorological, hydrological, and climatological processes. The USGCRP will examine linkages between land-atmosphere processes, their relationship to anthropogenic and other emissions, and the consequences of their deposition to the functioning of the biogeophysical and biogeochemical systems of southern Africa. This initiative is being built around a number of ongoing activities supported by the U.S., the international community, and African nations in the southern African region. 34 Implementation of the USGCRP in FY 2000 Carbon Cycle Science: An FY 2000 Initiative Rising atmospheric carbon dioxide concentration and its potential impact on future climate is an issue of global economic and political significance. The need to understand how carbon cycles through the Earth system is therefore critically important to our ability to predict any future climate change. Recent policy debates have demonstrated the need for a comprehensive, unbiased scientific understanding of sources and sinks of carbon dioxide on continental and regional scales, and how sinks might change naturally over time or be enhanced by human activities. The National Research Council's report, Global Environmental Change: Research Pathways for the Next Decade, specifically emphasizes the need for a comprehensive carbon cycle research strategy. The USGCRP is answering this call by establishing the Carbon Cycle Science Initiative. USDA, DOE, DOI, NASA, NSF, DOC/NOAA, and the Smithsonian will take part in this initiative. The new program is poised to provide critical unbiased scientific information on the fate of carbon dioxide in the environment to contribute to the ongoing public dialogue. The program will: take advantage of ongoing breakthrough advances in innovative scientific techniques to measure, monitor, observe, and model the carbon cycle, making it possible to examine the carbon cycle comprehensively as an integrated system; • provide the scientific foundation for estimating the capacity of land ecosystems and the ocean to sequester and store carbon dioxide released as a result of human activities; integrate modeling, observational, and process research to identify and quantify regional- to global-scale sources and sinks for carbon dioxide and other greenhouse gases; seek to understand how these sources and sinks will function in the future and provide this essential information for future climate predictions; and evaluate potential management strategies for enhancing carbon sequestration in the environment and in capture and disposal strategies. Achieving these objectives will provide information to policymakers and assist with the planning of future climate research activities. It will also provide valuable information to land and forest managers in the public and private sectors, and contribute to the natural resource management missions of agencies such as USDA and DOI. Full implementation of the new program will require a significant investment of resources and a new level of interagency coordination to ensure integration. Implementation of this program will be closely coordinated with international programs (e.g., the International Geosphere-Biosphere Programme and the World Climate Research Programme) to ensure a comprehensive international research strategy. Background Carbon dioxide is exchanged naturally between three active reservoirs: the atmosphere, the ocean, and land ecosystems. Human activity has increased the amount of carbon dioxide now being exchanged between these reservoirs. Carbon dioxide is initially added to the atmosphere as a product of combustion of fossil fuel and as emissions from conversion of forested land to agriculture. About half of what is added remains in the Implementation of the USGCRP in FY 2000 35 atmosphere, and the rest is taken up by the other two reservoirs-the ocean and land and freshwater ecosystems. Uptake of carbon dioxide by these reservoirs is commonly referred to as a "sink." While we can measure the concentration of carbon dioxide in the atmosphere quite accurately, measurements of storage of carbon in the ocean and land ecosystems are still considerably uncertain. For the past decade or more, independent approaches and innovative tools have greatly increased our understanding of how carbon dioxide is transported and stored in the Earth system. Most past research has tended to focus, appropriately, on each component of the carbon cycle separately. However, the carbon system is fundamentally integrated, and understanding of each component is now reaching the point where answers are available for how the carbon cycle operates as an integrated whole. This information is essential for use in designing and optimizing any potential carbon mitigation strategies envisioned in the next two decades. The storage reservoir, or sink, for carbon that we know the least about is the land ecosystem. Estimates from atmospheric and oceanic data and models have predicted that the terrestrial sink is larger in the Northern Hemisphere than in the Southern Hemisphere. Recent studies have attempted to refine the location of the Northern Hemisphere sink to a continental-scale region. While there is considerable debate about the magnitude and location of the terrestrial sink, there is strong evidence that it may be very significant. The ocean provides a long-term sink for carbon dioxide as a result of physical and biological processes that are largely independent of human control. However, humans may have inadvertently both created and destroyed terrestrial carbon sinks in the past from their manipulation of the land surface for settlement, food and energy production, and water management, for example. Climate also likely influences the magnitude of both the terrestrial and the oceanic sink. We have now reached a state of knowledge in the carbon cycle research arena where we can begin to tackle these questions and provide unbiased, scientific information to society about the location, magnitude, and cause of carbon sinks. Program Goal The overarching goal of the Carbon Cycle Science Program (CCS) is to answer the following fundamental questions: 1. What has happened to the carbon dioxide that has already been emitted by human activities (anthropogenic carbon dioxide)? 2. What will be the future atmospheric carbon dioxide concentration resulting from past and future emissions? FY 2000 Program Highlights The major focus of the initiative in FY 2000 will be on determining the location, magnitude, and cause of carbon sinks in North America, and how North America compares to other key regions, such as South America. Estimates of the Northern Hemisphere sink range widely; a program of integrated observations, process research, and modeling will narrow this range and provide a more accurate estimate of the North American terrestrial sink and its variability. The strategy will be to combine appropriate research approaches from the atmosphere, oceanic, terrestrial, and human dimensions aspects of Implementation of the USGCRP in FY 2000 37 |