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.