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Guarding against false discovery in large-scale dendroclimatology

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Measurements of tree-ring widths are the most widely-distributed and best replicated source of surrogate environmental information on the planet, and are one of the main archives used to estimate changes in regional and global climate during the past several centuries or millennia. Because the Northern Hemisphere ring-width network is now so large, it is more crucial than ever to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude certain records. It may be the case that a particular set of ring-width records are, for whatever reason, more tightly coupled to a particular climate factor than other records from the same region or species and, as a result, may be superior estimators of that factor’s past behavior. At the same time, it is known that selecting a small number of predictors from a large pool of potential candidates increases the likelihood of a Type I error. That effect may be particularly relevant to dendroclimatology because the total number of available ring-width records is often much larger than the number of records used to produce reconstructions of large-scale climate features. As an initial step, it would be helpful if paleoclimate reconstructions derived from tree rings described more explicitly the criteria used to select ring-width records as potential predictors and specified those records excluded by that screening. By comparing ring-width chronologies and their relations with climate against the standard set by thousands of records across the hemisphere, we should be better able to distinguish climate signals from proxy noise and produce more accurate reconstructions of climate during the late Holocene.

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Guarding against false discovery in large-scale dendroclimatology

  1. 1. GUARDING AGAINST FALSE DISCOVERY IN LARGE-SCALE DENDRO CHRONOLOGY Sco! St. George University of Minnesota Understanding Uncertainties in Paleoclimate and Paleoecology: Age Models, Proxy Processes, and Beyond | December 18, 2014
  2. 2. 3ASSERTIONS BASED ON TREE-RING DATA
  3. 3. COSMIC RAYS
  4. 4. “ … THERE WAS A CONSISTANT ” AND SIGNIFICANT RELATIONSHIP BETWEEN GROWTH OF THE TREES AND THE FLUX DENSITY OF GALACTIC COSMIC RADIATION. Dengel et al., 2009 New Phytologist
  5. 5. SOLAR CYCLE
  6. 6. “ SPECTRAL ANALYSIS ALSO SHOW ” THAT SIGNIFICANT PERIODICITIES OF ~11 YEAR, 54 YEAR, AND 204 YEAR PEAKS [IN TREE-RING DENSITY RECORDS] RESPOND TO THE SCHWABE CYCLE, THE FOURTH HARMONIC OF THE SUESS CYCLE, AND THE SUESS CYCLE, RESPECTIVELY. Duan and Zhang, 2014 Journal of Geophysical Research - Atmospheres
  7. 7. ATLANTIC MULTIDECADAL OSCILLATION
  8. 8. “ TUPELO HONEY YIELD-PER-HIVE ” [RECONSTRUCTED FROM TREE-RING WIDTHS] HAS OSCILLATED BETWEEN MULTIDECADAL-LENGTH PERIODS OF LOW AND HIGH YIELDS DURING THE PAST 211 YEARS AND IS ASSOCIATED WITH THE ATLANTIC MULTIDECADAL OSCILLATION. Maxwell et al., 2013 Agricultural and Forest Meteorology
  9. 9. LARGE-SCALE GEOPHYSICAL PHENOMENA SMALL SETS OF TREE-RING WIDTH DATA
  10. 10. BOTTOM-UP APPROACH
  11. 11. JUNE TEMPERATURE JULY TEMPERATURE AUGUST TEMPERATURE SEPTEMBER TEMPERATURE OCTOBER TEMPERATURE NOVEMBER TEMPERATURE DECEMBER TEMPERATURE JANUARY TEMPERATURE FEBRUARY TEMPERATURE MARCH TEMPERATURE APRIL TEMPERATURE MAY TEMPERATURE JUNE TEMPERATURE JULY TEMPERATURE AUGUST TEMPERATURE SEPTEMBER TEMPERATURE
  12. 12. p > 0.05
  13. 13. TYPE 1 ERROR
  14. 14. There are more than 3,200 publicly-available tree-ring records Pinus Picea Quercus Pseudotsuga Larix Nothofagus Austrocedris Phyllocladus Agathis Source: St. George, PAGES News, 2014 (and many more held by individual investigators).
  15. 15. FALSE DISCOVERY RATE
  16. 16. “ … THE EXPECTED PROPORTION ” OF REJECTED LOCAL NULL HYPOTHESIS THAT ARE ACTUALLY TRUE. Wilks, 2006 Journal of Applied Meteorology and Climatology
  17. 17. SYNOPTIC APPROACH
  18. 18. Pinus Picea Pseudotsuga Quercus Larix A This map illustrates the reasonably-large subset of the North American tree-ring width network C 36ºN 18ºN records records B 54ºN 72ºN 90ºN 180ºW 120ºW 60ºW 0º 60ºE 120ºE 180ºW 2000 1000 12% 6% 0º Source: St. George et al., Geophysical Research Le!ers, 2013 analyzed by this study.
  19. 19. STRONG WIDESPREAD DIRECT
  20. 20. -0.8 -0.6 -0.4 -0.2 +0.2 +0.4 +0.6 +0.8 correlation coefficient (ring-width vs. climate)
  21. 21. (a) Winter precipitation WINTER PRECIPITATION Source: St. George, Quaternary Science Reviews, 2014
  22. 22. Fri!s, H.C. Growth-rings of trees: their correlation with climate. Science 154, 973-975 (1966).
  23. 23. EL NIÑO SOUTHERN OSCILLATION
  24. 24. ENSO Source: St. George, Quaternary Science Reviews, 2014
  25. 25. WEAK(ER) UNCOMMON INDIRECT
  26. 26. ATLANTIC MULTIDECADAL OSCILLATION
  27. 27. Source: St. George, Quaternary Science Reviews, 2014 ATLANTIC MULTIDECADAL OSCILLATION
  28. 28. PACIFIC/ NORTH AMERICAN PATTERN
  29. 29. (d) Pacific/North-American PACIFIC/NORTH AMERICAN PATTERN Source: St. George, Quaternary Science Reviews, 2014
  30. 30. ENSO PNA 475/2270 139/2270 records records
  31. 31. p > 0.05
  32. 32. TYPE 1 ERROR
  33. 33. 3 POTENTIALLY-USEFUL APPROACHES TO ADDRESS THIS CHALLENGE
  34. 34. STA1TISTICAL SIMULATIONS
  35. 35. Dr. Dave Meko University of Arizona
  36. 36. EXACT SIMULATION
  37. 37. +200 0 precipitation anomaly (mm) -200 decadal target decadal ‘noise’ 1900 1920 1940 1960 1980 2000 Source: St. George and Ault, Journal of Geophysical Research - Atmospheres, 2011
  38. 38. FO2RWARD MODELLING
  39. 39. Dr. Eugene Vaganov Siberian Federal University
  40. 40. Source: Vaganov et al., In Dendroclimatology, 2010
  41. 41. Synthetic tree-ring records generated by a forward model (and modern climate data) Can we predict how local trees should respond to weak or remote climate influences? oW 120exhibit largely the same spatial pa!erns in climate response as real trees. 60oW 0o 60oE 120oE 75oN 90oN SOIL MOISTURE : TEMPERATURE Source: Xiaolu (Grace) Li, Cornell University
  42. 42. SE3LECTION CRITERIA
  43. 43. Pinus Picea Quercus Pseudotsuga Larix Nothofagus Austrocedris Phyllocladus Agathis Source: St. George, PAGES News, 2014 Because the global ring-width network is now so large, it is crucial to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude particular records.

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