White paper: The IPICS 2k Array: a network of ice core climate and climate forcing records for the last two millennia

Understanding present and future climate change depends on knowledge of natural climate variability. For example, observed rapid warming in the Arctic is due both to greenhouse gas forcing and to atmospheric dynamical changes associated with the Arctic Oscillation (AO). Determining the magnitude and frequency of AO changes in the past is a critical part of projecting how it will behave in the future under increased greenhouse gas forcing conditions. Significant efforts have been put forth to reconstruct the AO and other natural patterns of climate variability, such as the El Niño-Southern Oscillation, using high resolved (e.g. annual) paleoclimate proxy data from geological archives – lake sediments, corals, tree rings, etc. Syntheses of these data have been used to obtain estimates of global-scale changes in climate, providing key tests for the ability of numerical general circulation models to faithfully reproduce natural climate variability.

Considerable uncertainties remain in the reconstruction of past climate. Most notably, polar regions and high altitudes remain poorly represented, yet these regions encompass areas where the climate is changing more rapidly than anywhere else on the planet. Furthermore, knowledge of past climate forcings and feedbacks (greenhouse gases, solar variability, aerosols) remains uncertain. In both contexts, ice core records have a critical role to play because they provide perhaps the best – and in many cases the only – source of information.

Ice core records have been obtained from many locations in the Arctic and Antarctic, as well as on high altitude glaciers at low latitudes. However, most existing records are either at inadequate temporal resolution, or are too short to allow for quantitative reconstructions of climate and other environmental variables greater than one or two centuries in length (Fig. 1). Additional cores are needed that achieve both adequate length and high temporal resolution to be fully incorporated into climate reconstruction and modeling efforts. The IPICS 2k Array provides a framework for obtaining a network of such cores. Two thousand years (2k) is a critical time frame that includes both the industrial era and a significant length of time prior to the advent of anthropogenic influences on climate.