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Long droughts: Using natural climate archives to gage the risks of future “megadroughts”

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In the Biblical story of Joseph, following seven years of abundance, the Kingdom of Egypt was confronted by seven years of drought and famine. In the parlance of modern climate science, intervals with several consecutive extremely dry years are described as ‘“megadroughts”. In this short talk, I’ll describe how climate scientists combine clues from natural weather archives (including corals, tree rings, lake sediments, and many other sources) to reveal the history of ancient megadroughts across our planet. And I’ll highlight new research that combines these surrogate drought records with simulations from state-of-the-art climate models to help us better anticipate the risks of unusually persistent droughts during the coming century.

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Long droughts: Using natural climate archives to gage the risks of future “megadroughts”

  1. 1. Network Meeting of the Alexander von Humboldt Foundation | Bielefeld, Germany | October 18-20, 2017 LONG DROUGHTS USING NATURAL CLIMATE ARCHIVES TO GAGE THE RISKS OF FUTURE “MEGADROUGHTS”
  2. 2. EXPERIENCE
  3. 3. EXPERIMENTAL LAKES AREA, CANADA
  4. 4. THE HILLS LOOK LIKE SAWDUST, 
 REALLY, THAT COLOUR. I’VE NEVER SEEN IT WHERE THE GRASS DIDN’T TURN GREEN IN THE SPRING BEFORE. “ ” Jerry Murphy, Elnora Alberta (Canada) Globe and Mail, 1 July 2009
  5. 5. LONG SHORT
  6. 6. BY LOOKING FARTHER INTO THE PAST,WE ARE ABLE TO UNDERSTAND HOW DYNAMIC OUR EARTH REALLY IS.
  7. 7. Source: Mina Guli VERTICAL COLUMNS HAVE BEEN USED TO MEASURE FLOODS ON THE NILE SINCE THE EARLY 8th CENTURY.
  8. 8. DENDROCHRONOLOGY
  9. 9. ALEXANDER VON HUMBOLDT
  10. 10. SEVERAL EXAMPLES… SEEM TO CONFIRM THE IDEA THAT THERE ARE STILL TREES ON THE GLOBE OF A TREMENDOUS ANTIQUITY AND PERHAPS WITNESSES TO ITS MOST RECENT PHYSICAL REVOLUTIONS. “ ” Alexander von Humboldt Views of Nature
  11. 11. QUERCUS DOUGLASII Source: Dan Griffen
  12. 12. PINUS LONGAEVA
  13. 13. MOST TREE-RING RECORDS FROM NORTH AMERICA REFLECT THE EFFECTS OF WINTER (GREEN DOTS) OR SUMMER PRECIPITATION (BLUE DOTS). Source: St> George and Ault, Quaternary Science Reviews, 2014
  14. 14. ?WHAT HAVE WE LEARNED ABOUT PAST (AND FUTURE) DROUGHTS BY READING THE RINGS OF LONG-LIVED TREES?
  15. 15. 1Tree rings (and other natural climate archives) provide clear evidence that droughts have been longer lasting during the ‘recent’ past.
  16. 16. 7 7PLENTY FAMINE
  17. 17. THESE STUMPS TOOK ROOT IN A DRY MEDIEVAL PERIOD BEFORE BEING KILLED BY INCREASED PRECIPITATION AND SUBSEQUENT FLOODING. Source: Bryce Gray
  18. 18. During the 11th century, more than 40% of the western United States experienced drought, even when averaged over several decades. Sources: Cook et al. (2004). Long-term aridity changes in the western United States. Science 306:1015–1018; Cook et al., (2016), North American megadroughts in the Common Era: reconstructions and simulations. WIREs Climate Change, 7:411–432 .
  19. 19. 2The Earth’s climate does not require any unusual conditions to produce megadroughts. It only needs time and a bit of (bad) luck.
  20. 20. In order to get prolonged megadroughts in the western United States, the climate system needs to be “pushed’ by exotic external forcings that have not occurred during the more recent instrumental period. HYPOTHESIS
  21. 21. EL NIÑOSOUTHERN OSCILLATION
  22. 22. +TIME
  23. 23. MORE THAN ONE OUT OF THREE SIMULATIONS HAD (AT LEAST) ONE EVENT AS SEVERE AS THE BIGGEST 11th CENTURY MEGADROUGHT .
  24. 24. 3In the U.S. Southwest, future warming could make megadroughts almost certain. But mitigation would cut their risks in half.
  25. 25. SOUTHWESTERN UNITED STATES
  26. 26. Source: Ault et al. Science Advances, 2016
  27. 27. EXPERIENCE

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