Abrupt Climate Change in Drought and El Niño

Julia Cole Geosciences Department University of Arizona

Drought, 1999-2004 As of May 18, 2004 • Current drought ~6 years long • Pattern extends across the midlatitudes of the northern hemisphere • Results from temperature patterns in the tropical Pacific and Indian Oceans • Dire consequences!

US Map: Drought Monitor, http://www.drought.unl.edu/dm/monitor.html Photos: Arizona Daily Star (fire) and the New York Times (Lake Powell) The “perfect ocean for drought” - a consequence of abrupt climate change?

• Global warming: warmer than usual in western Pacific and Indian Oceans – Set up by an abrupt transition in 1976 to warmer/wetter conditions

• Natural variability: cooler than usual in eastern Pacific, due to La Niña – Shift to cooler conditions in late 1998, which have persisted

Tropical SST map: M. Hoerling, NOAA CDC Sudden warming in 1976 • Seen in paleoclimate records from Pacific and Indian Ocean corals (and shorter instrumental records) • Sets the stage for “perfect ocean” and long western drought

-5.5 -5.5 Western Indian Ocean temperature (Kenya) -5.3 -5 -5.1 -4.5 -4.9 -4 -4.7

-3.5 -4.5

-4.3 -3 Western Pacific Ocean temperature (Kiribati) -4.1 -2.5 1800 1850 1900 1950 2000

Tropical SST map: M. Hoerling, NOAA CDC

Coral Data: J. Cole, U of Arizona 40-year megadrought: 1560-1589 • Transition is abrupt • Duration is long! • How would we recognize a megadrought in its 1560-1589 early stages? Dry Wet -2 -1 0 1 2 5 Summer Drought Index 4 Southwest drought reconstruction 3 2 1 0 -1 -2 -3 -4 -5 Map: D. Stahle, U. Arkansas 1200 1300 1400 1500 1600 1700 1800 1900 2000 Data: E. Cook, Columbia Univ. Tree image: H. Grissino-Mayer, UTK Take-home messages

• Abrupt change can occur anywhere • Abrupt change in one region impacts other regions • Abrupt change has consequences for southwest water • Abrupt change can result from natural and human causes • We may be feeling the effects of abrupt change now!