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Abrupt Climate Change: Inevitable Surprises
to gradual climate change, the impacts of abrupt climate change are expected to be greater.
Wetlands are among the most important ecosystems on earth, due to their many “ecosystem services.” They serve as “kidneys of the landscape” by cleansing polluted waters, recharging aquifers, and protecting shorelines (Mitsch and Gosselink, 2000). Wetlands, including estuaries, provide protection for organisms and serve as nurseries for the young of many oceanic food chain species. Furthermore, wetlands can be important carbon sinks. Only recently valued for stabilization of water supplies, wetlands have been filled, drained, or ditched throughout history. In the United States, over half of wetland areas have been drained (Mitch and Gosselink, 2000).
Wetlands are particularly vulnerable to abrupt climate change, especially droughts. Along with lakes and rivers, wetlands are dependent on precipitation for the health of their associated ecosystems. The paleorecord of droughts recorded by wetlands provides an indication of the sensitivity of these areas to climate change. These records are useful for predicting the frequency of abrupt climate change and the sensitivity of water bodies to future climate change. The impacts of abrupt climate changes will be exacerbated because of alteration to the natural environment from the impoundment of rivers, depletion of fossil groundwater, and draining of wetlands.
Montane glaciers are among the most responsive indicators of climate change. Past records of glacial advance and retreat are important for understanding relative magnitudes of abrupt climate change. These records show that the global altitude drop of the equilibrium snow line during abrupt climate changes was of similar magnitude at widely scattered locations, implying that an overall cooling of the atmosphere took place, not a redistribution of the heat balance (Broecker and Denton, 1989; Lowell, 2000; Broecker, 2001). Loss of montane glacier volume has been more or less continuous since the nineteenth century, but loss in the last decade has accelerated (Dyurgerov and Meier, 2000). The loss of montane glaciers in the tropics is dramatic, and in a warmer world this loss may extend to many temperate locations used for recreation.
Ice sheets are linked to abrupt climate change because melting of Greenland or the West Antarctic ice sheet would add directly to global sea level rise and to possible changes in the thermohaline circulation (Manabe and Stouffer, 1997). Much attention has been focused on the possibility of a rapid collapse of the West Antarctic ice sheet. Recent geological and glaciological evidence points to a stable but net decay since the last ice age (Conway et al., 1999), but with considerable uncertainty about future trends