Figure 1.5

Figure 1.5. An annually dated ice core record from central Greenland that reveals changes in: the extent of polar atmospheric circulation (PCI; high values indicate more of the northern hemisphere covered by polar air-masses) with an approximately 2600-year repeating cycle (O'Brien et al., 1995); accumulation of snow (Meese et al., 1994); methane (CH4) (Blunier et al., 1995) and _18O (Dansgaard et al., 1993); worldwide glacier expansions and their relative magnitudes (Denton and Karlen, 1973); various climate proxy records (Harvey, 1980); the Cockburn glacier advance in North America and the Younger Dryas (Figure 1.4). Letters represent peaks in each cycle with A equivalent to the Little Ice Age. GISP2 is the U.S.- sponsored Greenland Ice Sheet Project Two and GRIP is its European counterpart, the Greenland Icecore Project.