| Summary: | The rate of change in Northern Hemisphere temperature in the past century strongly suggests that we are now in a period of rapid global climate change. Also, the climate in the mid-Atlantic is quite sensitive to larger scale climate variation, which affects the frequency and severity of storminess, drought, and flooding. Evidence for regional scale sensitivity to larger scale variations in climate is based on modern meterological observations from the past 100 years, tree-rings from the past 300 years, and measurements from marine sediment and ice cores covering the past several thousand years. The ice-core data are particularly interesting, since they illustrate the potential for rapid reorganizations in climate. Human activity during the past century enhances sensitivity to such climate variation and change. There are increasing risks associated with climate extremes because of the anthropogenic alteration of watersheds. Due to increases in nutrient loading to watersheds, nitrogen flux per unit flow has increased over time. Wet years now have different consequences in coastal receiving waters such as Chesapeake Bay than equivalent wet years in previous centuries. In addition, increasing anthropogenic demands for water mean that regional drought can have increasing adverse impacts. Future shifts in patterns of climate variability, toward either extreme (wetter or dryer), would have big impacts in the mid- Atlantic region.
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