Abrupt Climate Change Ernie Agee 6 April 2005

 Abrupt Climate Change (ACC) Periodic and extreme shifts in the climate system in one decade or less (during the past 100,000 years of climate record).  ACC could happen today, resulting in far-reaching impacts for human society and ecosystems - including energy consumption and water supply demands.  Key Research Areas for Understanding ACC a) ocean circulation, b) sea-ice/land-ice behavior, c) hydrologic cycle, d) dynamical modes of atmosphere/nonlinear (chaotic) effects, e) climate models that reorganize the thermohaline circulation (THC) employing high resolution ocean components.  Chronic 'vs.' (Acute) Abrupt Climate Change Chronic - Milankovitch, Volcanoes, Solar, GHG etc. Acute - Volcanoes, GHG, etc.  Examples of Chronic: Wisconsin Glacier (Milankovitch); Little Ice Ages (Solar); 20th Century Warming (Volcanoes; GHG)  Examples of Acute: Year Without a Summer (Tambora /1816); "Glacial" Winter in Eastern 2/3 N. America in 76/77 (dynamical mode/14 day westward propagating wave); Dec '89; 2004 Florida Hurricane Season (?) (Dustbowl Era remains unexplained!)

 It is very normal to have abnormal weather; and climate is the statistical ensemble of weather events.  ACC crosses the threshold of "normal" variation; and generally requires a trigger mechanism such as, a) a perturbation in a chaotic dynamical system, b) reorganization of the THC, c) volcano, d) solar  External forcing mechanisms can damp out chaotic behaviors over time; chronic changes can produce ACC (e.g., freshwater balance of the N. Atlantic due to CO2 warming).  Climate models may fail to anticipate ACC.  Solar variability cannot be ignored. Although thermal forcing by GHG to Solar is 4 to 1, there are no precise models that predict the solar luminosity and its variability (i.e., the Solar Parameter); 11-year cycle, 22-year cycle; Gleissberg Cycle; Quiet Periods; Plages 'vs.' Sunspots; Solar Max Mission Satellite).  Climate Model Prediction "must" pass all tests posed by available data sets; and climate change predictions "must stand the test of time." There is no room for "Heliogeophysical Enthusiasts"!