FIGURE 2.3 Climate data from the GISP2 core, central Greenland, showing changes about 8,200 years ago probably caused by outburst flooding from around the melting ice sheet in Hudson Bay (Barber et al., 1999) and affecting widespread regions of the globe. The event punctuated generally warm conditions not too different from recently, so warmth is not a guarantee of climate stability. Accumulation and temperature reflect conditions in Greenland, chloride is wind-blown sea-salt from beyond Greenland, and calcium is continental dust probably from Asia (Biscaye et al., 1997). Forest-fire smoke likely is from North America, and methane probably records global wetland area. Data are shown as approximately 50-year running means. Accumulation from Alley et al. (1993) and Spinelli (1996), chloride and calcium from O’Brien et al. (1995), and fire data shown as a 50-year histogram of frequency of fallout from fires (Taylor et al., 1996), expressed as ratios to their average values during the approximately 2,000 years just prior to the Little Ice Age. Temperature is calculated as a deviation from the average over the same 2,000 years, from oxygen-isotopic data of ice (Stuiver et al., 1995), assuming a calibration of 0.33 per mil per degree C (Cuffey et al., 1995). Methane concentrations from the GISP2 core (heavier line; Brook et al., 1996) and the GRIP core (Blunier et al., 1995) are shown in parts per billion by volume (ppb). Note that some scales increase upward and others downward, as indicated, so that all curves vary together at the major events. Modified from Alley et al. (1997).

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