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Disentangling the decadal ‘knot’ in high-resolution paleoclimatology

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Even after more than a century of coordinated monitoring, instrumental weather observations are still too short to adequately constrain decadal or multidecadal behavior in the Earth’s climate system. Leading climatologists and climate modelers have called for the wider application of high-resolution proxy records to decadal variability and prediction studies, and our community has responded by producing new paleoclimate products that specifically target this type of ‘intermediate-term’ behavior. But we now also know our medium changes that message: the biological and geological systems that encode climate information into natural archives often also alter the original ‘input’, usually due to either seasonal filtering or non-climatic persistence. In this talk, we’ll discuss some of the challenges inherent to the use of high-resolution proxies to study decadal or multi-decadal climate variability, and suggest strategies that might clarify how climate acts on those timescales. And we’ll also present a new theoretical framework that could help paleo-scientists evaluate competing ideas about the causes of decadal- or multi-decadal events known to have occurred during the past one or two millennia.

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Disentangling the decadal ‘knot’ in high-resolution paleoclimatology

  1. 1. DISENTANGLING THE DECADAL ‘KNOT’ IN HIGH-RESOLUTION PALEOCLIMATOLOGY SCOTT ST. GEORGE TOBY AULT MARA McPARTLAND Second International TERENO Conference | Berlin, Germany | October 10, 2018
  2. 2. LONG TERM
  3. 3. Source: Estes et al., Nature Ecology and Evolution, 2018 MOST OBSERVATIONAL STUDIES IN ECOLOGY BASED ON AUTOMATED SENSORS (A), REMOTE SENSING (R), OR FIELD STUDIES (F) ARE CONDUCTED OVER A FEW YEARS OR LESS.
  4. 4. Source: LACCORE, University of Minnesota
  5. 5. WHAT IS THERE TO BE GAINED BY LOOKING INTO THE PAST?
  6. 6. SLOWALIENRARE
  7. 7. HIGH-RESOLUTION BI0- AND GEO-ARCHIVES CAN HELP SHED LIGHT ON DECADAL PHENOMENON AND THEIR UNDERLYING PROCESSES… …BUT THESE APPLICATIONS REQUIRE US TO ADDRESS SEVERAL CHALLENGES INVOLVED WITH RECOVERING ’SLOW’ CLIMATE SIGNALS FROM NATURAL RECORDERS.
  8. 8. MITCHELL 1976
  9. 9. CLIMATE IS NOW RECOGNIZED AS BEING CONTINUOUSLY VARIABLE, ON ALL SCALES OF TIME. “ ” J. Murray Mitchell Quaternary Research, 1976
  10. 10. Source: Huybers and Curry, Nature, 2006
  11. 11. … THE CENTURY-LONG SPAN OF TYPICAL CLIMATE CHANGE PROJECTIONS DOES NOT FIT THE DECADAL OUTLOOK OF RESOURCE MANAGERS AND THOSE PLANNING INFRASTRUCTURE INVESTMENTS. “ ” Mark Cane Nature Geoscience, 2010
  12. 12. MANDELBROT WALLIS 1968
  13. 13. WE SHALL SPEAK OF “JOSEPH-WILD” BEHAVIOR WHEN THE WETTEST DECADE WITHIN A CENTURY INCLUDES AN EXTRAORDINARY “TERM” OF WET YEARS. “ ” Benoit Mandelbrot and James Wallis Water Resources Research, 1968
  14. 14. DECADAL/ MULTI-DECADAL VARIABILITY
  15. 15. 1900 1920 1940 1960 1980 2000 -3 -2 -1 0 1 2 3 cm/month SINCE THE BEGINNING OF THE 20TH CENTURY, THE SAHEL REGION HAS EXPERIENCED SEVERAL DECADAL OR MULTIDECADAL ‘RUNS’ OF PERSISTENTLY HIGH OR LOW RAINY SEASON PRECIPITATION. Source: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington
  16. 16. Source: Ault, T. R., & St George, S. (2010). The magnitude of decadal and multidecadal variability in North American precipitation. Journal of Climate, 842–850. STRONG DECADAL VARIABILITY IN WINTERTIME CLIMATE HAS CAUSED RAINFALL, RIVER FLOW, AND EXTREME FLOODS IN NORTHERN CALIFORNIA TO BE HIGHLY SYNCHRONIZED SINCE THE 1930s.
  17. 17. COLORADO RIVER Source: Ralph Earlandson
  18. 18. THE COLORADO RIVER PROVIDES WATER TO 40 MILLION PEOPLE, BUT YEARLY FLOWS HAVE BEEN BELOW THE LEGAL ALLOCATION FOR MOST OF THE PAST TWO DECADES. Source: United States Bureau of Reclamation, Lower Colorado region 1920 1940 1960 1980 2000 5x106 107 1.5x107 2x107 acre-feet/yr
  19. 19. INSTRUMENTAL CLIMATE OBSERVATIONS MODEL SIMULATIONS
  20. 20. … THE USE OF HIGH-RESOLUTION PROXY DATA SHOULD BE EXPANDED BECAUSE THE SHORT OBSERVATIONAL RECORD AND MODEL UNCERTAINTY ARE UNABLE TO SIMULATE [DECADAL CLIMATE VARIABILITY]… “ ” Vikram Mehta et al., 2011 Bulletin of the American Meteorological Society
  21. 21. Source: Dan Griffen 1DECADAL EVENTS IN TERRESTRIAL SYSTEMS
  22. 22. 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 . DURING THE 11TH CENTURY, MORE THAN 40% OF THE WESTERN UNITED STATES EXPERIENCED DROUGHT, EVEN WHEN AVERAGED OVER SEVERAL DECADES.
  23. 23. Source: Balanzategui, Daniel, et al., An 810-year history of cold season temperature variability for northern Poland. Boreas 47.2 (2018): 443-453. THE 800-YR WINTER TEMPERATURE RECONSTRUCTION PRODUCED BY THE GFZ TREE-RING LABORATORY INCLUDES SEVERAL PROLONGED RUNS OF EXTREME COLD OR WARM YEARS IN NORTHERN POLAND.
  24. 24. 2EXTENDED RECORDS OF DECADAL CLIMATE MODES
  25. 25. Source: MacDonald, G. M., & Case, R. (2005). Variations in the Pacific Decadal Oscillation over the past millennium. Geophysical Research Le ers. HIGH-RESOLUTION PROXIES HAVE BEEN USED TO PRODUCE MULTI-CENTURY LONG ESTIMATES OF LEADING DECADAL CLIMATE MODES SUCH AS THE PDO.
  26. 26. KEITH BRIFFA
  27. 27. TREE RINGS ARE NOT THERMOMETERS OR RAIN GAUGES. “ ” Keith Briffa and colleagues Climate Variations and Forcing Mechanisms of the Last 2000 Years, 1996
  28. 28. SIGNAL FIDELITY
  29. 29. DAW06 DAR01 BIO01 MAC05 G&S01 1700 1750 1800 1850 1900 1950 2000 Source: Kipfmueller, K. F., Larson, E. R., & St George, S. (2012). Does proxy uncertainty affect the relations inferred between the Pacific Decadal Oscillation and wildfire activity in the western United States? Geophysical Research Le ers, 39(4), L04703. INDEPENDENT PROXY ESTIMATES OF THE PACIFIC DECADAL OSCILLATION INDEX DO NOT AGREE WITH EACH OTHER DURING THE 18TH AND 19TH CENTURIES. PDO Positive (white) | PDO Negative (black)
  30. 30. AS IT STANDS, THE CURRENT DISAGREEMENT AMONG THE EXISTING PDO RECONSTRUCTIONS IS PROBLEMATIC FOR ANY ASSESSMENT OF PDO VARIABILITY AND PDO-RELATED IMPACTS OVER THE LAST SEVERAL HUNDRED YEARS. “ ” Ma hew Newman et al., 2016 Journal of Climate
  31. 31. SIGNAL DISTORTION
  32. 32. MARSHALL McLUHAN
  33. 33. BIOLOGY
  34. 34. MATALAS 1962
  35. 35. THESE LARGE VALUES OF SERIAL CORRELATION SUGGEST THAT THE NON-RANDOMNESS OF TREE-RING SEQUENCES IS DUE TO THE STORAGE OF FOOD PRODUCTS IN THE TREE RATHER THAN THE YEAR TO YEAR VARIATIONS OF RAINFALL OR SOIL MOISTURE. “ ” Nicholas Matalas, 1962 International Association of Scientific Hydrology Bulletin
  36. 36. STORAGE
  37. 37. HUYBERS ET AL 2015
  38. 38. Source: Huybers, K., Rupper, S., & Roe, G. H. (2015). Response of closed basin lakes to interannual climate variability. Climate Dynamics, 1–15. EVEN IF THE CLIMATIC ‘INPUTS’ TO A CLOSED BASIN HAVE LITTLE OR NO PERSISTENCE, LAKE LEVELS WILL EXHIBIT STRONG LONG-TERM MEMORY DUE TO HYDROLOGICAL STORAGE.
  39. 39. WE FIND THAT INTERANNUAL CLIMATE VARIABILITY ALONE CAN EXPLAIN MUCH OF THE DECADAL-TO-CENTENNIAL VARIATIONS IN THE LAKE-LEVEL RECORD. “ ” Kathleen Huybers et al., 2015 Climate Dynamics
  40. 40. DECADAL “KNOT”
  41. 41. PROGRESS ON THE INTERPRETATION OF OCEAN-LAND CONNECTIVITY WOULD GAIN FROM STUDYING THE RELATIONSHIP BETWEEN LAND (E.G., TREE RINGS) AND OCEAN PROXIES (E.G., CORALS AND SHELLS). “ ” Christophe Cassou et al. Bulletin of the American Meteorological Society, 2018
  42. 42. IIMPROVING ACCESS TO GLOBAL MULTIPROXY NETWORKS
  43. 43. Sources: Emile-Geay, J., Mckay, N. P., Kaufman, D. S., Gunten, Von, L., Wang, J., Anchukaitis, K. J., et al. (2017). Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era. Scientific Data, 4, 1–33. Map created by Lara Klippel, Johannes Gutenberg University THE PAGES 2K CONSORTIUM HAS RELEASED A GLOBAL DATASET WITH MORE THAN 690 TEMPERATURE-SENSITIVE PROXIES SPANNING THE COMMON ERA.
  44. 44. CORAL-HYDRO2K MULTICHRON Constraining modeled multidecadal climate variability in the Atlantic using proxies derived from marine bivalve shells and coralline algae Tropical ocean hydroclimate and temperature from coral archives
  45. 45. IIADOPTING A “MORE NUANCED” APPROACH TO DECADAL CLIMATE MODES
  46. 46. PACIFIC DECADAL OSCILLATION
  47. 47. Source: Newman, M., Alexander, M. A., Ault, T. R., Cobb, K. M., Deser, C., Di Lorenzo, E., et al. (2016). The Pacific Decadal Oscillation, Revisited. Journal of Climate, 29(12), 4399–4427.
  48. 48. A MORE NUANCED APPROACH THAT TARGETS ONE OR MORE OF THE DIFFERENT PROCESSES THAT CONTRIBUTE TO PDO-RELATED VARIABILITY WOULD LIKELY LEAD TO AN UNDERSTANDING ABOUT HOW SUCH PROCESSES HAVE VARIED IN THE PAST, AND THEIR POTENTIAL INTERRELATIONSHIPS. “ ” Ma hew Newman et al. Journal of Climate, 2016
  49. 49. IIISUPPORTING PALEOCLIMATE INTERPRETATION VIA EXPLICIT HYPOTHESIS TESTING
  50. 50. Source: Cook et al., 2014: Pan-continental droughts in North America over the last millennium. Journal of Climate, 27, 383–397. HIGH-RESOLUTION PROXIES OFTEN FEATURE DECADAL OR MULTIDECADAL EVENTS, BUT IT’S NOT CLEAR WHETHER LONG-LASTING CLIMATE EXCURSIONS ARE THE PRODUCT OF UNUSUAL EXTERNAL FORCINGS.
  51. 51. INTERANNUAL VARIABILITY + TIME OUT-OF-SAMPLE CLIMATE STATES
  52. 52. NULL HYPOTHESISThe characteristics of megadrought in the western US (as reconstructed by tree rings) are consistent with those arising from a stochastically forced, linearly damped system with stationary statistics.
  53. 53. Drought Area Index (%) Source: Ault, T. R., St George, S., Smerdon, J. E., Coats, S., Mankin, J. S., Carrillo, C. M., et al. (2018). A robust null hypothesis for the potential causes of megadrought in western North America. Journal of Climate, 31(1), 3–24. EVEN WHEN STATISTICAL MODELS ARE CONDITIONED ON CLIMATE DATA FROM THE LATE 20TH CENTURY (ONLY), THEY STILL PRODUCE SYNTHETIC MEGADROUGHTS WHEN ALLOWED TO RUN FOR A MILLENNIUM.
  54. 54. 1000YEARS
  55. 55. DECADAL/ MULTI-DECADAL VARIABILITY
  56. 56. THE FAMINE STELA Source: WIkipedia User Morburre
  57. 57. GILGAMESH AND THE BULL OF HEAVEN
  58. 58. JOSEPH INTERPRETING PHARAOH'S DREAM
  59. 59. PROXY ARCHIVES
  60. 60. HIGH-RESOLUTION BI0- AND GEO-ARCHIVES CAN HELP SHED LIGHT ON DECADAL PHENOMENON AND THEIR UNDERLYING PROCESSES… …BUT THESE APPLICATIONS REQUIRE US TO ADDRESS SEVERAL CHALLENGES INVOLVED WITH RECOVERING ’SLOW’ CLIMATE SIGNALS FROM NATURAL RECORDERS.
  61. 61. @sco stgeorge

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