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DECADAL VARIABILITY IN TREE-RING RECORDS
SCOTT ST. GEORGE | UNIVERSITY OF MINNESOTA
Source: Laura Anne Heller
Decadal-To-Multidecadal Variability In The Earths Climate Viewed Through The Lens Of Ancient Trees
University of Minnesota Johannes Gutenberg-Universitt Mainz
Helmholtz-Zentrum Geesthacht
?WHY DO TREE-RING WIDTHSEXHIBIT SO MUCH VARIANCE ON DECADAL AND MULTIDECADAL TIMESCALES?
BIOLOGY
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
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
CLIMATE
PACIFIC DECADAL
OSCILLATION
Mean summer (JJA) PDSI
LAG-1 AC
DR. EDWARD COOK DR. DAVID STAHLE
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
CLIMATEBIOLOGY
DR. DAVID MEKO UNIVERSITY OF ARIZONA
Source: Meko, Ph.D. dissertation, 1981
1Are decadal or multidecadal pa!erns spatially coherent across large tree-ring networks?
MAP COLORADOUPPER COLORADO BASIN
Source: Nevada Tourism Media Relations
COLORADO RIVER
DR. TOBY AULT CORNELL UNIVERSITY
HOW DOES BETWEEN-CHRONOLOGY COHERENCE VARY ACROSS TIMESCALES?
Source: Meko et al., Geophysical Research Le!ers, 2007
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.
INTERANNUAL (H) DECADAL (M),
MULTIDECADAL AND CENTENNIAL (L)
MOST RECORDS SHOW STRONG COHERENCE AT HIGHER FREQUENCIES, BUT WEAKER AGREEMENT AT LOWER FREQUENCIES.
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.
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
2What detrending methods are best when trying to recover these intermediate frequency signals?
NAM2K PHASE 2 TREE-RING NETWORK
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.05
0.1
0.15
0.2
0.25
0.3Mean 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.
UPPER MISSOURI BASIN
-0.15 -0.1 -0.05 0.05 0.1 0.150
20406080
100120
Standard chronologies
Signal-free chronologies0. 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
0 0.1 0.2 0.3 0.4 0.50.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24Median 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.
DECADAL VARIABILITY
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
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
DR. BENOIT MANDELBROT MARCH 2007
Source: Baillie, Journal of Econometrics, 1996
TREE-RING WIDTHS HAVE OFTEN USED TO ILLUSTRATE LONG-MEMORY BEHAVIOR IN NATURE.