The last decade has also seen remarkable progress toward understanding the patterns and processes of climatic change over the last ca. 40,000 years (40 kyrs). Radiocarbon provides the tight chronological framework needed to unravel the exact response of the climate system to astronomical forcing over the last glacial to interglacial cycle, as well as to understand the decade- to millennia-scale (``sub-Milankovitch'') variability that is superimposed on this low-frequency component of variability. The COHMAP (Cooperative Holocene Mapping Project) group took up where the CLIMAP (Climate Mapping, Analysis and Prediction) effort left off, providing an international catalyst in efforts to map out the patterns of global climate change over the past 18,000 years using a variety of proxy data sources [ COHMAP, 1988; Wright et al., 1993]. Through the powerful combination of empirical paleoenvironmental reconstructions and climate model simulations for successive 3 kyr intervals (18,000 years ago [18 ka] to present), COHMAP and others have demonstrated the central role of Milankovitch forcing, along with the response of the climate system to this forcing, in explaining much of the observed low-frequency climatic variance of the last 18 kyrs [ COHMAP, 1988; Markgraf et al., 1992; Porter et al., 1992; Jarvis, 1993; R. Webb et al., 1993; Wright et al., 1993].
Despite remarkable progress toward understanding how forcing both
external and internal to the climate system generated the observed patterns
of change during the late Quaternary, puzzles still remain. Many areas of
the Earth outside mid-latitude North America and Europe still lack
well-dated networks of data. Controversy over the thermal history of the
low-latitude surface oceans continues [ Webster and Streten, 1978;
Bush and Colinvaux, 1990; Anderson and Webb, 1994;
Guilderson et al., 1994; Sikes and Keigwin, 1994;
 Thunell et al., 1994]. Uncertainty over the last 20 kyrs of sea level and ice-sheet history has been greatly reduced, although the glacial volumes of the East Antarctic and North American ice-sheets are still uncertain [ Fairbanks, 1989; Ruddiman, 1994].