• Document how the activities of humans have affected the global environment and climate and determine how these effects can be differentiated from natural variability. Describe what constitutes the natural environment prior to human intervention.

  • Explore the question of what the natural limits are of the global environment and determine how changes in the boundary conditions for this natural environment are manifested.

  • Document the important forcing factors that are and will control climate change on societal timescales (season to century). Determine what the causes were of the rapid climate change events and rapid transitions in climate state.

Paleoclimate records come from a variety of archives (e.g., tree rings, ice cores, marine and lake sediments, corals, historical documents) and are available at a variety of resolutions and age ranges. Paleoclimate records also provide different types of information ranging from proxy to direct. Furthermore, they contain evidence of both environmental response to change and the potential causes of change. A broad range of types of records will be required to understand climate change. No one type of record will suffice, since no single record type can provide the temporal, spatial, proxy, and direct measurements required to develop the global array required to understand past changes in climate.

Our most detailed view of climate comes from the past few decades of instrumented observations. To take the fullest advantage of paleoclimate records, calibration between paleoclimate and instrumented records is essential. Landmark examples already exist, notably the calibration between CO2 measurements in ice cores and CO2 observations in the atmosphere. Preliminary comparisons between coral, tree ring, and ice core paleoclimate series and instrumental series of, for example, ENSO and the NAO are extremely encouraging.

Paleoclimate studies calibrated to instrumental series offer the “missing years” prior to the introduction of Earth-observing satellites and instrumented observations. These missing years cannot be produced by any other known methodology. Furthermore, through the hindsight offered by paleoclimate records, observing programs will be able to more accurately assess natural climate variability, patterns, trends, and signal to noise. Finally, paleoclimate records offer the climate modeling community a bold opportunity for testing climate response and forcing on a variety of timescales and resolutions heretofore untouched.

Nine guiding principles for future research are as follows:

  1. Development of a global array of highly resolved, continuous, precisely dated, multivariate paleoclimate records that sample the atmosphere, ocean, cryosphere, and land. For the identification of environmental change over the past two millennia, annual to decadal resolution will be required, and for longer timescales decadal- to centennial-scale resolu-



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