The Earth’s climate and environmental history has been long, amazingly complex,and marked by enormous changes. The challenge to this element of the USGCRP is to provide a quantitative understanding of the Earth’s past environment and to define the envelope of natural environmental variability within which the effects of human activities on the planet’s biosphere, geosphere, and atmosphere can be assessed.

Figure 4
(See Appendix E for additional information)

    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natural archives, such as: lake and ocean sediments, tree rings, wind-blown deposits, coral, and ice cores, as well as historical documents.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.