Large-scale low-frequency variability has emerged as a priority for climate research, but instrumental observations are not long enough to characterize this behavior or gage its impacts on dependent geophysical or ecological systems. As the leading source of high-resolution paleoclimate information in the middle- and high-latitudes, tree rings are essential to understand low-frequency variability prior to the instrumental period. But even though tree rings possess several advantages as climate proxies, like other natural archives they also have their own particular impediments. In this lecture, Dr. St. George will describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how the fingerprint of decadal and multidecadal climate variability encoded within ancient trees varies across the hemisphere.

1. LARGE-SCALE DENDROCHRONOLOGY
AND LOW-FREQUENCY CLIMATE VARIABILITY
KlimaCampus Colloquium, University of Hamburg | July 9 2015
Sco St. George
University of Minnesota

4. DECADAL
VARIABILITY

5. Source: Mohino et al., Climate Dynamics, 2011
SAHEL PRECIPITATION ANOMALIES
(FILTERED TO EMPHASIZE LOW-FREQUENCY VARIABILITY)

6. PACIFIC
DECADAL
OSCILLATION

7. 1900 1920 1940 1960 1980 2000 2020
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
discharge (cfs) at Grand Forks, North Dakota
Source: United States Geological Survey
THE RED RIVER OF THE NORTH,
LEAST STATIONARY RIVER IN THE USA

8. DECADAL PREDICTION,
A NEW FIELD OF STUDY,
FOCUSES ON TIME-EVOLVING
REGIONAL CLIMATE CONDITIONS
OVER THE NEXT 10-30 YR,
WHICH IS A TIME PERIOD OF INTEREST
TO INFRASTRUCTURE PLANNERS,
WATER RESOURCES MANAGERS, AND OTHERS.
“ ”
Meehl et al., 2009
Bulletin of the American Meteorological Society

9. INSTRUMENTAL CLIMATE
OBSERVATIONS

10. -34°CFORT SNELLING, MINNESOTA
30.1.1820

11. 1900 1920 1940 1960 1980 2000 2020
-4
-3
-2
-1
0
1
2
3
4
Source: Dr. Nate Mantua, University of Washington
LOW-FREQUENCY VARIABILITY IN THE NORTH PACIFIC
AS REPRESENTED BY THE PACIFIC DECADAL OSCILLATION INDEX

12. A LIMITATION OF
THE INSTRUMENTAL RECORD
IS THAT IT SPANS
AT MOST
A FEW REALIZATIONS
OF DECADAL VARIABILITY.
“ ”
Solomon et al., 2011
Bulletin of the American Meteorological Society

13. Source: Deser et al., Annual Review of Marine Science, 2010
DISTRIBUTION OF SEA-SURFACE TEMPERATURE OBSERVATIONS
FROM THE INTERNATIONAL COMPREHENSIVE
OCEAN ATMOSPHERE DATA SET
Percentage of months with at least one measurement

14. MODEL SIMULATIONS

16. Source: Delworth and Zeng, Geophysical Research Le ers, 2012
INVESTIGATING DECADAL TO MULTICENTENNIAL VARIABILITY
OF NORTHERN HEMISPHERE SURFACE AIR TEMPERATURES
IN A 4000-YR CONTROL SIMULATION

17. IN CCSM4, CENTENNIAL VARIABILITY ARISES PRIMARILY
AS A THERMODYNAMIC RESPONSE TO EXPLOSIVE VOLCANISM.
Source: Ault et al., Geophysical Research Le ers, 2013

18. … 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

20. Because temperate and boreal forests are so extensive,
trees that form annual rings are very common.
Trees routinely a ain ages in excess
of several hundred years.
ADVANTAGES OF TREE-RING WIDTHS
AS CLIMATE PROXIES
Source: St. George, Quaternary Science Reviews, 2014
Tree-ring records have annual resolution and
the accuracy of their dating is confirmed by a
rigorous cross-comparison procedure.

21. Tree-ring display at elementary school
Photograph:Tom Swetnam

22. Dr. David Meko University of Arizona

23. Source: Meko et al., Geophysical Research Le ers, 2007
MULTI-CENTURY RECONSTRUCTIONS OF COLORADO RIVER FLOW
FROM TREE-RING WIDTHS

24. PROXY ARCHIVES

26. … PRECIPITATION RECONSTRUCTIONS
THAT ARE ENTIRELY BASED ON
TREE-RING WIDTH CHRONOLOGIES
MAY CONSIDERABLY OVERESTIMATE
THE TRUE PERSISTENCE
OF REGIONAL RAINFALL REGIMES.
“ ”
Bunde et al., 2013
Nature Climate Change

28. 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

29. 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”

30. Dr. Toby Ault Cornell University

31. 1DECVAR ALONG THE CENTRAL PACIFIC COAST

32. 2THE FIDELITY OF PALEO-PDO ESTIMATES

33. 3STRATEGIES TO TRACK PALEO-DECVAR

35. RINGS
IN THE BRANCHES OF
SAWED TREES SHOW
THE NUMBER OF YEARS
AND, ACCORDING TO THEIR
THICKNESS,
THE YEARS WHICH WERE
MORE OR LESS
DRY.
“ ”
Leonardo da Vinci

36. 36
EARLYWOOD
LATEWOOD
ONE GROWTH RING

37. HOW MANY
(COMPLETE) TREE RINGS
ARE VISIBLE
IN THIS MICROPHOTOGRAPH?

39. HOW MANY
(COMPLETE) TREE RINGS
ARE VISIBLE
IN THIS MICROPHOTOGRAPH?

40. 1871 1872 1873 1874
Source: Dr. Dan Griffin, University of Minnesota

41. Source: Dr. Dan Griffin, University of Minnesota
NORTHWESTERN NEW MEXICO

42. CRATER LAKE NATIONAL PARK

43. 1809 1811 181218081807
Source: Sarah Appleton, University of Minnesota

46. IF NO RING WAS FORMED IN A GIVEN YEAR
THAT CREATES A FURTHER COMPLICATION
INTRODUCING AN ERROR
IN THE CHRONOLOGY ESTABLISHED BY
COUNTING RINGS
BACK IN TIME.
“ ”
Dr. Michael Mann
Penn State News, February 6. 2012

47. Source: Esper et al., Dendrochronologia, 2013
If tree-ring records from Europe are shi ed back one year,
their strong correlation with long temperature records disappears.

48. 0%
2%
4%
6%
8%
20°N
40°N
60°N
80°N
Latitude
Percentage of locally-absent rings
b
Picea Quercus
Pinus Pseudotsuga
Larix Other genera
Source: St. George et al., Geophysical Research Le ers, 2013

50. Source: Büntgen et al., Nature Climate Change, 2014
Radiocarbon measurements of a subfossil pine (Pinus cembra)
show the same 1.2% increase in 14C from AD 774 to 775.

51. ±0

52. 1DECVAR ALONG THE CENTRAL PACIFIC COAST

53. Source: Dr. Greg Brooks, Geological Survey of Canada
RED RIVER, CENTRAL CANADA

54. Source: Flickr user kc7cbf

55. ‘WHITE’
total annual precipitation (mm)
ANNUAL PRECIPITATION IN DES MOINES, IOWA
Source: Global Historical Climate Network

56. Central Pacific Coast

57. 1920 1960 2000
−400
0
400
Regional winter precipitation anomalies (mm)
Ault and St. George, Journal of Climate, 2010
CENTRAL PACIFIC COAST

58. 1920 1960 2000
−400
0
400
Regional winter precipitation anomalies (mm)
Ault and St. George, Journal of Climate, 2010
CENTRAL PACIFIC COAST

59. THE HISTORY OF METEOROLOGY
IS LITTERED WITH
THE WHITENED BONES OF CLAIMS
TO HAVE DEMONSTRATED
THE EXISTENCE OF RELIABLE CYCLES
IN THE WEATHER.
“ ”
William James Burroughs
Weather Cycles: Real or Imaginary?

61. Source: California Department of Water Resources
Florsheim, JL, De inger, MD, 2007. Climate and
floods still govern California levee breaks.
Geophysical Research Le ers.

62. Source: Ault and St. George, Journal of Climate, 2010
STRONG DECADAL VARIABILITY SYNCHRONIZES
RAINFALL, STREAMFLOW, AND HAZARDS IN NORTHERN CALIFORNIA.

63. A STRONG ATMOSPHERIC RIVER
CAN TRANSPORT 7-15X
THE WATER IN THE MISSISSIPPI RIVER

64. … IN TODAY’S EMBANKED SYSTEM,
81% OF LEVEE BREAKS
ALONG CENTRAL VALLEY RIVERS
OCCURRED FLOODS GENERATED BY
WINTERTIME [ATMOSPHERIC RIVERS]
WITH ONLY 15% OCCURRING
DURING SNOWMELT FLOODS.
“ ”
Florsheim and De inger, 2015
Geomorphic Approaches to Integrated Floodplain Management
of Lowland Fluvial Systems in North America and Europe,

66. UNDER THE ‘HASSELMANN’ PARADIGM,
THE LOW-FREQUENCY COMPONENTS
ARE DRIVEN BY
THE STOCHASTIC HIGHER-FREQUENCY ONES
AND ARE NOT PREDICTABLE.
days
TIMESCALE
VARIANCE
decades
high
low
months

67. ARE
TREE-RING WIDTH RECORDS
ABLE TO TRACK
THIS PARTICULAR
NARROWBAND FEATURE?

68. CRATER LAKE NATIONAL PARK

69. ) Winter precipitation
Source: St. George, Quaternary Science Reviews, 2014
WINTER PRECIPITATION

70. Source: Dr. Dan Griffin, University of Minnesota
QUERCUS DOUGLASII

71. 1700 1750 1800 1850 1900 1950 2000
Tree growth (anomalies)
−0.4
0.4
0
1650
ring-width records
mean of set
Source: St. George and Ault, Journal of Geophysical Research - Atmospheres, 2011
TREE-RING WIDTH RECORDS FROM BLUE OAKS
INDICATE THE 20TH CENTURY WAS UNUSUALLY DECADAL.

72. Source: Dr. Kevin Anchukaitis, University of Arizona
✔

73. days decadesmonths
UNDER THE ‘BJERKNES’ PARADIGM,
THE LONGER TIMESCALES MODULATE THE SHORTER ONES
THROUGH OCEAN PROCESSES
AND THEREFORE MAY BE PREDICTABLE.
TIMESCALE
VARIANCE
high
low

74. Source: NASA

75. 2THE FIDELITY OF PALEO-PDO ESTIMATES

77. PEYTO LAKE, CANADA

78. (c) Summer temperat
Source: St. George, Quaternary Science Reviews, 2014
SUMMER TEMPERATURE

79. Source: Fri s et al., Journal of Applied Meteorology, 1971
SEASONAL PRESSURE ANOMALIES OVER THE NORTH AMERICAN SECTOR
RECONSTRUCTED FROM 49 RING-WIDTH RECORDS

80. A LONG CLIMATIC RECORD
CAN SERVE TO IDENTIFY
THE RANGE OF POSSIBLE CLIMATES
AND THE CHARACTERISTICS OF
POSSIBLE CLIMATE “MODES”.
“ ”
Fri s et al., 1971
Journal of Applied Meteorology

82. Source: St. George, Quaternary Science Reviews, 2014
ENSO

83. PACIFIC
DECADAL
OSCILLATION

84. PDO
D’ARRIGO AND WILSON, 2006
“ON THE ASIAN EXPRESSION OF THE PDO”
D’ARRIGO ET AL., 2001
“TREE-RING ESTIMATES OF
PACIFIC DECADAL CLIMATE VARIABILITY”
BIONDI ET AL., 2001
“NORTH PACIFIC DECADAL CLIMATE VARIABILITY
SINCE 1661”
GEDALOF AND SMITH, 2001
“INTERDECADAL CLIMATE VARIABILITY AND
REGIME-SCALE SHIFTS IN PACIFIC NORTH AMERICA”
MACDONALD AND CASE, 2005
“VARIATIONS IN THE PACIFIC DECADAL OSCILLATION
OF THE PAST MILLENNIUM”

85. Source: Newman et al,, in revision

87. … DROUGHTS OCCURRED
DURING PERIODS OF BOTH WARM AND COOL
KUROSHIO EXTENSION SSTS
AND PERHAPS DURING
POSITIVE AND NEGATIVE PDO,
ALTHOUGH THIS IS DEPENDENT ON
WHICH PDO RECONSTRUCTION IS USED.
“ ”
McCabe-Glynn et al., 2013
Nature Geoscience

88. Source: Newman et al,, in revision
POOR REPRODUCIBILITY BETWEEN VARIOUS PDO RECONSTRUCTIONS
CALLS TO QUESTION THEIR COLLECTIVE FIDELITY.

89. Source: Michael Chow
BOULDER, COLORADO

90. Source: Kipfmueller et al., Geophysical Research Le ers, 2012
BLACK : WARM PHASE
WHITE: COLD PHASE
GREY: NO DATA
ANY CONCLUSION THAT EXTENSIVE WILDFIRES ARE MORE OR LESS COMMON
WHEN THE PDO IS IN ONE PHASE OR THE OTHER
DEPENDS ENTIRELY ON THE CHOICE OF PDO RECONSTRUCTION.

91. WHY HAS IT BEEN
SUCH A CHALLENGE
TO RECONSTRUCT THIS ASPECT
OF DECADAL VARIABILITY
IN THE NORTH PACIFIC?

93. OCEAN SURFACE HEAT FLUX (VIA THE ALEUTIAN LOW)
OCEAN MEMORY
THE KUROSHIO-OYASHIO CURRENT
+
+
THE PDO
=
Source: Newman et al,, in revision

94. SMALL SETS
OF TREE-RING WIDTH
DATA
LARGE-SCALE
GEOPHYSICAL
PHENOMENA

95. Source: St. George, Quaternary Science Reviews, 2014
PDO

96. Pinus
Picea
Quercus
Pseudotsuga
Larix
Nothofagus
Austrocedris
Phyllocladus
Agathis
Source: St. George, PAGES Magazine, 2014
There are more than 3,200 publicly-available tree-ring records
(and many more held by individual investigators).

99. 3STRATEGIES TO TRACK PALEO-DECVAR

100. Source: Gray et al., Geophysical Research Le ers, 2003
Most dendroclimatic studies first reconstruct an annually-resolved target
variable, and then apply some form of filter to emphasize decadal behavior.

101. IMPROVING ESTIMATES
OF INTERMEDIATE-SCALE
VARIABILITY

102. TREE-RING WIDTHS BECOME SMALLER
AS THE TREE GETS OLDER
BECAUSE OF THE GEOMETRICAL CONSTRAINT CREATED
BY ADDING A VOLUME OF WOOD
TO A STEM OF INCREASING RADIUS.

103. [AGE-SIZE TRENDS IN TREE-RING WIDTH]
SHOULD BE THOUGHT OF AS
A NONSTATIONARY, STOCHASTIC PROCESS
THAT MAY, AS A SPECIAL CASE,
BE MODELED AS
A DETERMINISTIC PROCESS.
“ ”
Cook and Briffa, 1990
Methods of Dendrochronology

104. (A) the ‘raw’
ring-width data

105. (B) the ‘detrended’
ring-width
index

106. 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

109. PRESERVING
DECADAL VARIANCE
IN DENDROCLIMATIC
RECONSTRUCTIONS

110. Dr. Toby Ault Cornell University

111. CHRONOLOGY RECONSTRUCTION
mean-value function
representing annual tree growth
across many dozens or hundreds of trees
quantitative estimate
of a climate variable
derived from
one or several tree-ring chronologies

112. 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.

113. Chronology ‘A’
Chronology ‘B’
Chronology ‘C’
Chronology ‘D’
Chronology ‘E’
Chronology ‘F’
Chronology ‘G’
Chronology ‘H’
Chronology ‘I’
Chronology ‘J’
Reconstruction
10 predictors76421
THE NESTED RECONSTRUCTION APPROACH
GENERATES A NEW MODEL FOR EACH SUBSET OF PREDICTORS.

114. Source: Cook et al., Journal of Quaternary Sciences, 2010
THE NORTH AMERICAN DROUGHT ATLAS USES A NETWORK OF MOISTURE-
SENSITIVE TREE-RING RECORDS TO ESTIMATE CHANGES IN DROUGHT CONDITIONS
ACROSS THE CONTINENT.

115. 450 km
A FIXED SEARCH RADIUS AROUND EACH GRID POINT
DEFINES THE ZONE OF LOCAL CONTROL
EXERCISED BY THE METHOD IN SELECTING
CANDIDATE TREE-RING PREDICTORS
OF PDSI.
Source: Cook et al., Journal of Climate, 1999

116. CHOOSING
ALTERNATIVE DECADAL TARGETS
FOR RECONSTRUCTION

117. OCEAN SURFACE HEAT FLUX (VIA THE ALEUTIAN LOW)
OCEAN MEMORY
THE KUROSHIO-OYASHIO CURRENT
+
+
THE PDO
=
Source: Newman et al,, in revision

118. IF THE RELATIVE IMPORTANCE
OF THESE CONTRIBUTIONS VARIES,
THEN THE APPARENT TELECONNECTION
FROM THEIR SUM (THE PDO) COULD BE
NONSTATIONARY
EVEN IF TELECONNECTIONS
TO THE INDIVIDUAL PDO PROCESSES
WERE FIXED.
“ ”
Newman et al., in revision
Bulletin of the American Meteorological Society

120. Source: Zanche in et al., Climate of the Past, 2015
PACIFIC/
NORTH AMERICAN
PATTERN

121. THESE RESULTS CALL FOR
STRENGTHENED COOPERATION
BETWEEN THE CLIMATE PROXY
AND CLIMATE MODELING COMMUNITIES
IN ORDER TO IMPROVE OUR KNOWLEDGE
ABOUT THE EARLY 19TH-CENTURY PNA
AND TO SOLVE THE RELATED
RECONSTRUCTION-SIMULATED DISCREPANCY.
“ ”
Zanche in et al., 2015
Climate of the Past

123. Dr. David Meko University of Arizona

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

125. TREE-RING RECORDS ARE ABLE TO TRACK
DECADAL CLIMATE VARIABILITY, AT LEAST IN SOME CASES.
BUT WE NEED TO SPECIFICALLY TEST
THEIR FIDELITY AT THOSE TIMESCALES.

126. TREE-RING ESTIMATES OF DECADAL CLIMATE MODES
ARE NOT CONSISTENT PRIOR TO THE 20TH CENTURY.
THAT LACK OF AGREEMENT COULD TELL US SOMETHING
ABOUT THE STABILITY OF TELECONNECTIONS
ASSOCIATED WITH DECADAL MODES.

127. ACCURATELY EXTRACTING DECADAL SIGNALS FROM TREE-RING PROXIES
IS A LONGSTANDING PROBLEM.
THE PALEO-COMMUNITY MIGHT NEED TO ADOPT (AND TEST)
NEW STRATEGIES TO DEAL WITH
OUR PARTICULAR DECADAL ‘CONUNDRUM’.

128. SCOTT ST. GEORGE
DEPARTMENT OF GEOGRAPHY, ENVIRONMENT AND SOCIETY
UNIVERSITY OF MINNESOTA
@SCOTTSTGEORGE