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Solar ghosts: Weighing the evidence for sunspot cycles in fossil trees

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In their study of tree rings from the Chemnitz Fossil Forest (Germany), Luthardt and Rößler (2017) claim to identify a regular near-11-yr cyclicity in growth, and present that pattern as evidence of the influence of the Schwabe solar cycle (Usokin and Mursula, 2003) on climate and forest productivity during the early Permian. If correctly interpreted, these fossil tree rings would indicate the sunspot cycle was the dominant influence on interannual variability in Earth’s climate during this period and that it has been a consistent aspect of our Sun’s behavior for at least the past 300 m.y. We argue the fossil tree-ring record from Chemnitz does not constitute reliable evidence of solar activity during the Permian because the individual tree-ring sequences are not correctly aligned (dendrochronologically dated) and, as a result, the mean ring-width composite is not a meaningful estimate of year-to-year variations in tree growth in this ancient forest.

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Solar ghosts: Weighing the evidence for sunspot cycles in fossil trees

  1. 1. WEIGHING THE EVIDENCE FOR SUNSPOT CYCLES IN FOSSIL TREES Paleoclimate Seminar | Johannes Gutenberg-Universität Mainz | November 15, 2017
  2. 2. 1613CE
  3. 3. GALILEO GALILEI Portrait by Justus Sustermans
  4. 4. JUNE 23, 1613 Source: The Galileo Project/M. Kornmesser
  5. 5. LETTERS ON SUNSPOTS (1613)
  6. 6. 1843CE
  7. 7. SAMUEL SCHWABE
  8. 8. 11-YR SOLAR CYCLE
  9. 9. WE NOW HAVE A 400-YR LONG RECORD OF SUNSPOT NUMBERS, WHICH CLEARLY SHOWS A NEAR-PERIODIC 11-YR CYCLE (AS WELL AS OTHER CHANGES). Source: Robert Rohde
  10. 10. Source: Greg Kopp, University of Colorado 1880 1900 1920 1940 1960 1980 2000 2020 1360.2 1360.4 1360.6 1360.8 1361 1361.2 1361.4 1361.6 1361.8 W/m2 TOTAL SOLAR IRRADIENCE VARIES IN PHASE WITH THE SCHWABE CYCLE WITH AN AMPLITUDE OF ABOUT 0.1% AROUND A MEAN VALUE OF 1361.5 W/M2.
  11. 11. ?WAS THE 11-YR SCHWABE CYCLE A REGULAR COMPONENT
 OF OUR SUN’S BEHAVIOR PRIOR TO CE 1600?
  12. 12. A.E. DOUGLASS Source: University of Arizona
  13. 13. PRACTICALLY ALL THE GROUPS OF TREES INVESTIGATED SHOW THE SUNSPOT CYCLE OR ITS MULTIPLES — THE SOLAR CYCLE BECOMES MORE CERTAIN AND ACCURATE AS THE AREA… INCREASES OR THE TIME OF A TREE RECORD EXTENDS FARTHER BACK… “ ” A.E. Douglass Climatic Cycles and Tree Growth, 1919
  14. 14. 1978CE
  15. 15. … LITTLE CONVINCING EVIDENCE HAS YET BEEN PRODUCED FOR REAL CORRELATIONS BETWEEN SUNSPOT CYCLES AND THE WEATHER/CLIMATE ON THE 11- AND 22-YEAR TIIMESCALES. “ ” A.B. Pi ock Reviews of Physics and Space Physics, 1978
  16. 16. DATA SELECTION AUTOCORRELATION SMOOTHING POST HOC HYPOTHESI
  17. 17. HAD [DOUGLASS] BUT KNOWN IT, THE SUNSPOT RECORD IS PROBABLY BETTER PRESERVED IN THE ISOTOPIC CHEMISTRY OF THE RINGS THAN IN THE RING-WIDTH SIGNAL! “ ” Brian Luckman Tree Rings, Environment and Humanity, 1996
  18. 18. 14C
  19. 19. RADIOCARBON MEASUREMENTS (MADE ON TREE-RING-DATED WOOD SAMPLES) HAVE BEEN USED TO RECONSTRUCT SUNSPOT NUMBERS DURING THE HOLOCENE. Source: Solanki et al., Nature, 2004
  20. 20. Pinus Picea Quercus Pseudotsuga Larix Nothofagus Austrocedris Phyllocladus Agathis Source: St. George, Past Global Changes Magazine, 2014
  21. 21. CHEMNITZ FOSSIL FOREST
  22. 22. LATE PERMIAN (260 MA) Source: Dr. Ron Blakey, Northern Arizona University
  23. 23. CHEMNITZ FOSSIL FOREST
  24. 24. Source: Luthardt and Rößler, Geology, 2017
  25. 25. Source: Luthardt and Rößler, Geology, 2017
  26. 26. 43FOSSIL TREES
  27. 27. Source: Luthardt and Rößler, Geology, 2017 AFTER ALIGNING TREE-RING WIDTH SEQUENCES FROM 11 TREES, LUTHARDT AND RÖßLER CLAIMED TO IDENTIFY A REGULAR NEAR-11-YR CYCLICITY IN GROWTH.
  28. 28. LIKE TODAY SUNSPOT ACTIVITY CAUSED FLUCTUATIONS OF COSMIC RADIATION INPUT TO THE ATMOSPHERE, AFFECTING CLOUD FORMATION AND ANNUAL RATES OF PRECIPITATION, WHICH ARE REFLECTED IN THE TREE-RING ARCHIVE. “ ” Luthardt and Rößler Geology, 2017
  29. 29. 11-YR CYCLE 300MILLION YEARS
  30. 30. THEY WERE STUNNED BY HOW CLEARLY THEY COULD SEE THE [SUNSPOT] CYCLES. “ ” The Economist January 21, 2017
  31. 31. ICH AUCH 🤔
  32. 32. WEIRD ERRORS
  33. 33. DOCUMENTATION OF SUNSPOT ACTIVITY FOR THE PAST 1 M.Y. BY 10BE AND 13C ISOTOPES IN ICE CORES AND TREE RINGS SUGGEST AN AVERAGE PERIODICITY OF 11.12 YR (USOSKIN ET AL., 2015). “ ” Luthardt and Rößler Geology, 2017
  34. 34. SHORT SERIES
  35. 35. DATING HOLOCENE TREES
  36. 36. STRONG CYCLES
  37. 37. Gleissberg (88-yrs) and de Vries (205-yrs) cycles do not occur consistently through the Holocene reconstruction4 of total solar irradiance (TSI) (Fig 3). Figure 3. Spectra of the TSI reconstruction for different time windows in the Holocene. Red points mark frequencies with significant spectral power (p=0.1). Figure 6. Blue lines - proportion of records that have significant power (p=0.1) at each frequency. Red dashed line - the expected proportion. Frequencies highlighted with a red point are significantly (p=0.1) above this background. Number of records is shown by the lower red line. Orange bands - frequencies that have significant power in TSI reconstruction. Dashed pale blue lines - 88 and 205 year-1 cycles. • No window has more records with Gleissberg (88- yrs) or de Vries (205-yrs) cycles than expected. • There are not significantly more 88 or 205 year cycles in time windows with these periods in TSI Figure 2. Distribution of tree-ring width records analysed. Records in red have significant spectral power near the Schwabe cycle. We hypothesise that if solar variability is an important determinant of climate, these cycles will occur more frequently in proxy records during time windows with the cycles in TSI. We test this with a compilation (Fig 4) of high- resolution Holocene proxy-climate records collated from various sources. Figure 4. Proxy data used in at least one time window. No tree-ring records were used. For each time window, we • Select proxy records that met standards for resolution and coverage • Identify significant frequencies (Fig 5). • Report the percent of records that have significant power at each frequency (Fig6). Figure 5. Red points - frequencies that have significant (p=0.1) spectral power in the time window 0-2000 BP. Orange bands - frequencies that have significant power in TSI. Is there robust evidence of solar variability in palaeoclimate proxy data? Richard J. Telford, Kira Rehfeld & Scott St. George Richard.Telford@uib.no Department of Biology, University of Bergen & Bjerknes Centre for Climate Research, Norway @richardjtelford kira.rehfeld@awi.de Alfred Wegner Institute, Potsdam, Germany stgeorge@umn.edu University of Minnesota @ scottstgeorge 1. Schurer et at (2014 Nat. Geosci. 7: 104–108 2. See examples at https://quantpalaeo.wordpress.com/category/solar-variability/ 3. St George (2014) Quat. Sci. Res. 95, 132-150 4. Steinhilber et al (2012) PNAS 109:5967-5971 The strength of the relationship between variations in solar activity and climate is contentious. Some authors find that solar variability has relatively little effect1, but numerous papers report evidence of the impact of solar variability on palaeo-proxy climate data. This suggests that solar variability is an important determinant of climate variability. This evidence needs to be treated with caution because of 1. methodological problems in many papers2 • eyeball-correlations of proxies • multiple testing • chronological adjustments to maximise correlations • confounding of solar variability by volcanic forcing during last millennium 2. publication bias • few papers reporting non-significant results are published To avoid these problems we undertake a systematic review of high-resolution proxy data to detect solar cycles. Figure 1. a) Spectral power of annual sunspot numbers . 90% significance level assumes the multi- taper spectrum is locally white. b) spectral power of the Herring Alpine (Alaska) tree-ring widths record. c) percentage of the ring-width records that are significant at p=0.1 by frequency. We test for the 11-year Schwabe cycle in a sample of tree-ring data3 from the World Data Centre for Paleoclimatology. • Interval AD 1750 - 1950 • 752 tree-ring width records met criteria for signal quality and sample depth • Annual sunspot counts show a clear spectral peak centred at 11 years (Fig. 1a). Some tree-ring width records have significant power at 11 years-1 (Fig. 1b), but fewer than 10% of the records exhibit significant power at p=0.1 (Fig. 1c), and these are scattered geographically (Fig 2). We conclude that we do not find robust evidence of Schwabe (11-yrs), Gleissberg (88-yrs) or de Vries (205-yrs) cycles in palaeoclimate data. We are working to increase the number of proxy records included in this analysis and perform additional tests. PDF available at https://quantpalaeo.wordpress.com/?p=1242 This work was supported by the Norwegian Research Council project PalaeoDrivers
  38. 38. ? WERE THE CHEMNITZ TREE-RING SERIES CORRECTLY-ALIGNED (DENDROCHRONOLOGICALLY DATED) AND IS THEIR MEAN RING-WIDTH CURVE A MEANINGFUL ESTIMATE OF TREE GROWTH IN THIS ANCIENT FOREST?
  39. 39. CONCURRENT WIDE OR NARROW RINGS ARE THE MOST RELIABLE CHRONOLOGICAL MARKERS IN PROPERLY DATED TREE-RING SEQUENCES .
  40. 40. WHAT A COLOR PLOT OF 100 YEARS OR SO OF A DATED TREE-RING SEQUENCE LOOKS LIKE.
  41. 41. ? WERE THE CHEMNITZ TREE-RING SERIES CORRECTLY-ALIGNED (DENDROCHRONOLOGICALLY DATED) AND IS THEIR MEAN RING-WIDTH CURVE A MEANINGFUL ESTIMATE OF TREE GROWTH IN THIS ANCIENT FOREST?
  42. 42. RING NUMBER 10 20 30 40 50 60 70 80 AVERAGE growth HIGH growth LOW growth COLOR PLOT ILLUSTRATING THE ALIGNMENT OF THE CHEMNITZ FOSSIL TREE-RING SEQUENCES SUGGESTED BY LUTHARDT AND RÖßLER (2017). Source: St. George and Telford, Geology, 2017
  43. 43. 50 60 70 80Source: St. George and Telford, Geology, 2017
  44. 44. 11TREE-RING SERIES 43FOSSIL TREES
  45. 45. -4 -2 0 2 4 1 10 20 30 40 50 60 70 80 Computed mean ring-width Mean ring-width reported by L+R17 Ring number THE MEAN RING-WIDTH COMPOSITE REPORTED IN THEIR ARTICLE DOESN’T MATCH THE AVERAGE OF THEIR 11 TREE-RING SERIES.
  46. 46. DATA SELECTION AUTOCORRELATION SMOOTHING POST HOC HYPOTHESI
  47. 47. SEQUENCES OF THE RESULTING RING INDICES WERE SMOOTHED USING A THREE-POINT MOVING AVERAGE SMOOTHER. “ ” Luthardt and Rößler Geology, 2017
  48. 48. WHITE NOISE
  49. 49. WE WANT TO UNDERLINE THE DIFFICULTY IN DIRECTLY COMPARING ANY MODERN TREES, FORESTS, AND THEIR SITUTATION WITH THAT OF EXTINCT PLANTS, THEIR PALEOGEOGRAPHIC, PALEOCLIMATIC, ENVIRONMENTAL, AND TAPHONOMIC RESPONSE. “ ” Luthardt and Rößler Geology, 2017
  50. 50. Source: Luthardt and Rößler, Geology, 2017 “THEY WERE STUNNED BY HOW CLEARLY THEY COULD SEE THE [SUNSPOT] CYCLES.”
  51. 51. WHITE NOISE
  52. 52. … SIX OF ELEVEN SEQUENCES SHOW A DISTINCT POWER PEAK AT A PERIODICITY OF 9-12 YR, WHEREAS TWO SEQUENCES (K349 AND K6044) ARE STATISTICALLY ROBUST (P < 0.05). “ ” Luthardt and Rößler Geology, 2017
  53. 53. 2TREE-RING SERIES 43FOSSIL TREES
  54. 54. … TREE-RING SEQUENCES REFLECT A SENSITIVE FEEDBACK REACTION OF EARLY PERMIAN MONSOONAL PALEOCLIMATE TO VARIATIONS OF SOLAR IRRADIANCE. “ ” Luthardt and Rößler Geology, 2017
  55. 55. SOLAR IRRADIANCE WEATHER/CLIMATE TERRESTRIAL ORGANISMS
  56. 56. “ZOMBIE” THEORIES
  57. 57. @sco stgeorge

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