Click for larger image.Notes:
Fig. 1. Observed, zonally averaged, land-surface air-temperature anomalies (°C) as a function of latitude and time (7), together with the temperature record for the same interval from Upernavik, Greenland (72°47'N, 56°10'W, on the northwest coast of Greenland) (8). Global instrumental coverage is just sufficient to capture the rapid, concentrated warming at high northern latitudes in the 1920s, which is shown more dramatically at sites such as Upernavik.
Instrumental records reveal detailed, global information on abrupt, often societally disruptive, climate shifts. For example, the warming that occurred during the 20th century in many northern regions was concentrated in two rapid steps, suggestive of a juxtaposition of human-induced secular trend and interdecadal variability due to natural causes (7). The warming on the Atlantic side of the Arctic during the 1920s was 4ƒC or more in places (8) (Fig. 1). During the following decade, an extended drought often called the Dust Bowl had a lasting impact on the United States (9, 10). Such abrupt-onset, severe regional drought regimes have been infrequent in the United States during the instrumental period but more common elsewhere, including in the Sahel (11). The strong links in many regions between drought or flood and the El NiÒo-Southern Oscillation (ENSO) system (12) focus attention on ENSO regime shifts (13).
Large, abrupt, and widespread climate changes with major impacts have occurred repeatedly in the past, when the Earth system was forced across thresholds. Although abrupt climate changes can occur for many reasons, it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious. Unpredictability exhibited near climate thresholds in simple models shows that some uncertainty will always be associated with projections. In light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies
R.B. Alley, J. Marotzke, W.D. Nordhaus, J.T. Overpeck, D.M. Peteet, R.A. Pielke Jr., R.T. Pierrehumbert, P.B. Rhines, T.F. Stocker, L.D. Talley, J.M. Wallace, "Abrupt Climate Change", Science, Volume 299, Pages 2005-2010 (March 2003).
Full paper (PDF)
Document contributed by Than-Van Nguyen and assembled by Colin Rego, Northeastern University, 3/2004.
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