Figure 1.4

Figure 1.4. Left: As deduced from an ice core in central Greenland the Younger Dryas was an abrupt return to near glacial conditions (15 +/- 3oC cooling relative to today from the _18O record (left) which is a proxy for temperature where more negative values equal colder temperature), decreased accumulation of snow, decreased methane (CH4) and increased atmospheric dust that lasted approximately 1300 years and punctuated the transition from glacial to interglacial climates. Figure modified from Alley et al. (1993), Grootes et al. (1993), Brook et al. (1996). Right: This high resolution calcium record from the same ice core indicates the relative amount of dust in the atmosphere over Greenland and thus documents other abrupt, frequent and massive changes in climate that characterized the glacial portion of the ice core record. Figure modified from Mayewski et al. (1997).