Paleoenvironmental records are derived from a wide variety of natural archives, such as: lake and ocean sediments, tree rings, wind-blown deposits, coral, and ice cores, as well as historical documents. Chemical, isotopic, and ecological analyses of these records have demonstrated that the natural climate system has varied locally and globally over a far greater range than can be inferred from relatively short-term instrumental records. In most locations, instrumental records might provide 100 years of climate data, whereas an ice core might provide an annual climate record of 10,000 to 30,000 years. Understanding the natural environmental changes of our planet on long timescales (years to millennia) provides the context for understanding today's climate dynamics and for elucidating the impacts of natural versus anthropogenic influences. Reconstructing the historical climate record offers an enhanced understanding of the mechanisms controlling the Earth's climate system and, together with insight obtained from numerical modeling exercises, anticipates how the planet might respond to future environmental perturbations.
 

Key research challenges include:
1. Global Climate and Earth’s Environment: Documenting how the global climate and Earth’s environment have changed in the past and determining the factors that caused these changes; exploring how this knowledge can be applied to understand future climate and environmental change; and establishing the natural (baseline) environment prior to human intervention.
2. The Natural Limits of Global Environmental Variability: Exploring the natural limits and variability of our global environment and determining how changes in the boundary conditions of the environment are manifested.
3. Forcing Factors: Documenting the important forcing factors that have controlled past climate and examining how these forcing factors interact and have varied in significance over time; and investigating the causes of the rapid climate change events and rapid transitions in climate state observed in the paleo record and evaluating the potential for environmental "surprises" in the near- and long-term future.

Focus for FY 2000:
• The USGCRP will have completed the first global synthesis of paleoclimate within the context of global change research. This synthesis will be fashioned within the time frame of the last 100,000 years. The international research community will focus on establishing and understanding the temporal and spatial range of natural climate variability during the period prior to significant anthropogenic impact, and initiate the use of the paleorecord for improving the predictive ability of climate and environmental system models.
• The international paleoenvironmental data system, the World Data Center for Paleoclimate (Boulder, CO), will be in place and functioning. This will serve as the global data coordination, access, and archive point for the international research community and will include easy-access links to specialized national, regional and project databases.
• The USGCRP will have established a global network long-term paleoclimate records from corals, tree rings, ice cores, and other sources (some of which are up to 1,000 years long), and will develop statistical methodologies to link these disparate sources of climate data.
• Researchers will focus on calibrating the relatively short instrumental climate record to paleoclimate proxies, in order to assess climate change over decadal to centennial timescales.
• The USGCRP will have evaluated the hypothesis that the Arctic is one of the most sensitive regions for climate and environmental change, has undergone large changes over the last 1000 years, and, in magnitude and extent, is currently undergoing an unprecedented warming. Further, the program will have begun the development and evaluation of coupled atmospheric/oceanic/sea-ice climate models and high-resolution regional models to advance our understanding of the dynamic Arctic environment and its climatic linkages to the lower latitudes.
• The USGCRP will have a much clearer understanding of natural climatic variability within quasi-stable climatic states (i.e., glacial and interglacial times). Although climatic variation occurs within all periods, research will focus on establishing the predictability of abrupt and extreme climatic events and their spatial and environmental impact.
• Research will focus on characterizing the history of the warm pool in the tropical Pacific Ocean over the last 200-300 years. Researchers will establish the history of significant changes in surface temperature and/or areal extent of this water mass under varying climatic states. This information will be essential for understanding global climate dynamics and testing models under different boundary conditions.
• Paleoenvironmental research will initiate a special emphasis on the closely interlinked relationship between human societal evolution and climatic and environmental change, with special emphasis on the last 500,000 years. Researchers will aim for a clearer understanding of both the impact of a changing environment on human development (migration, adaptation) and human impact on the environment (burning, megafauna and vegetation change).
• The USGCRP will have a much clearer understanding of climate-induced vegetation and ecosystem change over the last 20,000 years, particularly in North America. This knowledge will allow us to improve estimates of future climate-induced vegetation and ecosystem change, as well as possible biophysical and biogeochemical feedbacks to the climate.