Strong variance at decadal and multidecadal timescales is a common feature of most tree-ring width records. But does this aspect of tree growth exhibit such long-memory behavior due to biology, climate, or some combination of the two factors? Understanding the origins of this behavior is crucial for efforts to evaluate the causes of decadal variability in the climate system. Presentation at Johann Gutenburg University (Mainz) on February 16, 2017.

1. DECADAL VARIABILITY
IN TREE-RING RECORDS
SCOTT ST. GEORGE | UNIVERSITY OF MINNESOTA

2. Source: Laura Anne Heller

4. Decadal-To-Multidecadal Variability In The Earth’s Climate
Viewed Through The Lens Of Ancient Trees
University of Minnesota
Johannes Gutenberg-Universität Mainz
Helmholtz-Zentrum Geesthacht

5. ?WHY DO TREE-RING WIDTHS
EXHIBIT SO MUCH VARIANCE
ON DECADAL AND MULTIDECADAL TIMESCALES?

7. BIOLOGY

9. WE FOUND
PERVASIVE AND SUBSTANTIAL
“LEGACY EFFECTS”
OF REDUCED GROWTH AND INCOMPLETE RECOVERY
FOR 1 TO 4 YEARS
AFTER SEVERE DROUGHT.
“ ”
Anderegg et al., 2015
Science

11. 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.
“ ”
Matalas, 1962
International Association of Scientific Hydrology Bulletin

12. CLIMATE

13. PACIFIC
DECADAL
OSCILLATION

15. Mean summer
(JJA) PDSI
LAG-1 AC

16. DR. EDWARD COOK DR. DAVID STAHLE

17. THE AR MODEL
OF THE INSTRUMENTAL PDSI
WAS ADDED TO
THE PREWHITENED TREE-RING ESTIMATES
AND THE RESULTING RECONSTRUCTION EXPLAINS
62% OF THE VARIANCE IN THE OBSERVED PDSI.
“ ”
Stahle et al., 2011
Geophysical Research Le ers

18. CLIMATEBIOLOGY

19. DR. DAVID MEKO UNIVERSITY OF ARIZONA

20. Source: Meko, Ph.D. dissertation, 1981

21. 1Are decadal or multidecadal pa erns spatially coherent
across large tree-ring networks?

22. MAP COLORADO
UPPER COLORADO BASIN

23. Source: Nevada Tourism Media Relations
COLORADO RIVER

24. DR. TOBY AULT CORNELL UNIVERSITY

25. HOW DOES BETWEEN-CHRONOLOGY COHERENCE
VARY ACROSS TIMESCALES?
Source: Meko et al., Geophysical Research Le ers, 2007

26. WE USE THE RBAR STATISTIC TO GAUGE THE MEAN CORRELATION BETWEEN A SINGLE TREE- RING
RECORD AND ALL OTHERS IN THE NETWORK AT INTERANNUAL (H), DECADAL (M), AND
MULTIDECADAL AND CENTENNIAL (L) TIMESCALES.

27. INTERANNUAL (H)
DECADAL (M),
MULTIDECADAL AND CENTENNIAL (L)
MOST RECORDS SHOW STRONG COHERENCE AT HIGHER FREQUENCIES, BUT WEAKER
AGREEMENT AT LOWER FREQUENCIES.

28. Source: Adapted from Ault et al., Journal of Climate, 2013
PALEO-PRECIPITATION RECONSTRUCTIONS FROM TREE RINGS HAVE LESS VARIANCE
AT LOW FREQUENCIES THAN THE ORIGINAL TREE-RING CHRONOLOGIES.

29. THE MOST OBVIOUS SOURCE OF
NONCLIMATIC PERSISTENCE
IN TREE-RING DATA
IS ERROR IN REMOVAL OF
THE GROWTH TREND
WHEN CONVERTING ANNUAL RING WIDTHS
TO TREE-RING INDICES.
“ ”
Meko, 1981
Doctoral dissertation, University of Arizona

30. 2What detrending methods are best when trying to
recover these ‘intermediate’ frequency signals?

32. NAM2K PHASE 2 TREE-RING NETWORK

34. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
0.05
0.1
0.15
0.2
0.25
0.3
Mean squared coherence
Frequency (1/f)
Signal-free version
of the age-dependent
spline-detrended chronology
Variance-stabilized standard version
of the age-dependent
spline-detrended chronology
Standard version
of the age-dependent
spline-detrended chronology
Variance-stabilized
signal-free version
of the age-dependent
spline-detrended chronology
Negative exponential chronology
FOR THESE TEMPERATURE-SENSITIVE TREES,
SIGNAL-FREE DETRENDING DOES INCREASE THE BETWEEN-
CHRONOLOGY COHERENCE AT LOW FREQUENCIES.

35. UPPER MISSOURI BASIN

36. -0.15 -0.1 -0.05 0.05 0.1 0.15
0
20
40
60
80
100
120
Standard chronologies
Signal-free chronologies
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
Number of chronologies
Between-tree correlation
Difference in RBAR
RBAR higher in SigFreeRBAR higher in Std

37. 0 0.1 0.2 0.3 0.4 0.5
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
Median coherence between neighboring chronologies
Negative-exponential detrended
Signal-free detrended
MEAN SQUARED
COHERENCE
BUT FOR MOISTURE-SENSITIVE TREES, SIGNAL-FREE DETRENDING DOES NOT AFFECT
THEIR AGREEMENT WITH NEIGHBORING CHRONOLOGIES ONE BIT.

38. DECADAL
VARIABILITY

39. … 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]…
“ ”
Mehta et al., 2011
Bulletin of the American Meteorological Society

40. ADVANTAGE
DISADVANTAGE
Short relative to
decadal timescales
Firmly grounded
in reality
Too sensitive to
volcanic forcing?
Simulations are much longer
than the timescale of interest
Long records
grounded in reality
Proxy systems may distort
or exaggerate decadal signals
THE DECADAL CLIMATE “CONUNDRUM”

41. DR. BENOIT MANDELBROT MARCH 2007

43. Source: Baillie, Journal of Econometrics, 1996
TREE-RING WIDTHS HAVE OFTEN USED TO ILLUSTRATE
LONG-MEMORY BEHAVIOR IN NATURE.