Much of what we know regarding variations in Earth's climate during the past millennium comes from tree rings. But tree rings, like other proxies, attenuate some climate signals but amplify others, and their fidelity at longer timescales is difficult to gage. Even though dendroclimatology is well-established, questions remain about the climate clues encoded in tree rings — particularly at decadal-to-centennial timescales.

1. HOW LONG DO TREES REMEMBER?
Climate Variability Across Scales Working Group | PAGES (Past Global Changes) | August 13, 2020

2. MUCH OF WHAT WE KNOW REGARDING VARIATIONS IN EARTH'S
CLIMATE DURING THE PAST MILLENNIUM COMES FROM TREE RINGS.
TREE RINGS, LIKE OTHER PROXIES, ATTENUATE SOME CLIMATE
SIGNALS BUT AMPLIFY OTHERS, AND THEIR FIDELITY AT LONGER
TIMESCALES IS DIFFICULT TO GAGE.
DENDROCLIMATOLOGY IS WELL-ESTABLISHED BUT QUESTIONS
REMAIN ABOUT THE CLIMATE CLUES ENCODED IN TREE RINGS —
PARTICULARLY AT DECADAL-TO-CENTENNIAL TIMESCALES.

5. MUCH OF WHAT WE KNOW
REGARDING VARIATIONS
IN EARTH'S CLIMATE
DURING THE PAST MILLENNIUM
COMES FROM TREE RINGS.

6. NEUKOM
ET AL
2019
NO EVIDENCE FOR
GLOBALLY COHERENT
WARM AND COLD PERIODS
OVER THE
PRE-INDUSTRIAL
COMMON ERA

8. Source: Emile-Geay et al., Scientific Data (2017)
IN 2017, THE PAGES 2K INITIATIVE RELEASED A GLOBAL, COMMUNITY-SOURCED DATABASE OF
TEMPERATURE-SENSITIVE PROXIES SPANNING THE PAST TWO MILLENNIA.

9. Source: Emile-Geay et al., Scientific Data (2017)

11. HURST
1956
THE PROBLEM OF
LONG-TERM STORAGE
IN RESERVOIRS

12. Source: Hurst, Hydrological Sciences Journal (1956)
TREE-RING WIDTHS WERE AMONG THE INITIAL TYPES OF EVIDENCE USED BY HURST TO DESCRIBE
LONG-RANGE PERSISTENCE IN HYDROLOGICAL AND GEOPHYSICAL TIME SERIES.

13. LOVEJOY
SCHERTZER
2012
STOCHASTIC AND SCALING
CLIMATE SENSITIVITIES: SOLAR,
VOLCANIC AND ORBITAL FORCINGS

14. Source: Lovejoy and Schertzer, Geophysical Research Le ers (2012)
BETWEEN 1 AND 500 YR, THEIR STOCHASTIC ESTIMATE OF CLIMATE SENSITIVITY
LEANS HEAVILY ON RECONSTRUCTIONS DERIVED MAINLY FROM TREE RINGS.

15. INTERNATIONAL
TREE-RING
DATABANK4,949 TOTAL RING-WIDTH
621 LATEWOOD WIDTH
619 EARLYWOOD WIDTH
575 MAXIMUM LATEWOOD DENSITY
31 OXYGEN-18
26 BLUE INTENSITY
24 CARBON-13
Accessed August 6, 2020

17. TREES
ARE NOT
THERMOMETERS
OR RAIN GAUGES.
“ ”
Keith Briffa and colleagues
Climate Variations and Forcing Mechanisms of the Last 2000 Years, 1996

18. TREE RINGS, LIKE OTHER
PROXIES, ATTENUATE SOME
CLIMATE SIGNALS BUT AMPLIFY
OTHERS, AND THEIR FIDELITY AT
LONGER TIMESCALES IS
DIFFICULT TO GAGE.

20. AGE/SIZE PERSISTENCE

21. Tree age
Ring width
AS TREES GROW LARGER WITH AGE, THEY ARE OBLIGED TO FORM NEW WOOD
ABOUT THE EVER-INCREASING CIRCUMFERENCE OF THEIR BOLE.

22. Source: Björkland et al., New Phytologist (2017)
MAXIMUM LATEWOOD DENSITY INCREASES AS TREES TRANSITION FROM JUVENILE TO MATURE
WOOD, BUT LATER DECREASES AS FEWER RESOURCES ARE USED TO THICKEN CELL WALLS.

23. COOK
ET AL
1995
THE ‘SEGMENT-LENGTH CURSE’
IN LONG TREE-RING
CHRONOLOGY DEVELOPMENT
FOR PALEOCLIMATIC STUDIES

24. TRADITIONAL TREE-RING STANDARDIZATION METHODS
WOULD SEEM TO
PLACE A FUNDAMENTAL LIMIT
ON THE RESOLVABILITY OF
VERY LOW-FREQUENCY CLIMATE FLUCTUATIONS
FROM TREE RINGS
WHEN CLIMATE CHANGES MORE SLOWLY
THAN THE TYPICAL LIFESPAN
OF THE TREES BEING STUDIED.
“ ”
Ed Cook et al., 1995
The Holocene

25. KLIPPEL
ET AL
2020
DIFFERING PRE-
INDUSTRIAL COOLING
TRENDS BETWEEN
TREE RINGS AND
LOWER-RESOLUTION
TEMPERATURE
PROXIES

26. Source: Klippel et al., Climate of the Past (2020)
COMPOSITES OF MARINE SEDIMENTS (ORANGE), LAKE SEDIMENTS (RED), AND GLACIAL ICE CORES
(BLUE) HAVE STRONG PRE-INDUSTRIAL COOLING TRENDS. BUT TREE RINGS (GREEN) DON’T!

27. AGE/SIZE PERSISTENCE

30. COULTHARD
ET AL
2020
THE LIMITS OF
FREELY-AVAILABLE
TREE-RING
CHRONOLOGIES

31. Source: Coulthard et al., Quaternary Science Reviews (2020)
TREE-RING SEQUENCES USUALLY EXHIBIT HIGH PERSISTENCE OVER SEVERAL YEARS DUE TO
BIOLOGY (ARISING FROM CARBOHYDRATE STORAGE OR NEEDLE RETENTION) OR CLIMATE (DRIVEN
BY LAGS IN TEMPERATURE OR HYDROLOGY).

32. REDSHIFT

33. TREE RINGS
ARE NOT
THE ONLY PROXY
WITH THESE KINDS
OF PROBLEMS…( )

34. HUYBERS
ET AL
2015
RESPONSE OF
CLOSED BASIN LAKES
TO INTERANNUAL
CLIMATE VARIABILITY

35. Source: Huybers et al.,Climate Dynamics (2015)
EVEN IF THE CLIMATIC ‘INPUTS’ TO A CLOSED BASIN HAVE LITTLE OR NO PERSISTENCE,
LAKE LEVELS WILL EXHIBIT STRONG LONG-TERM MEMORY
DUE TO HYDROLOGICAL STORAGE.

37. IN PRINCIPLE,
PROXY AND GCM DATA
SHOULD YIELD A CONSISTENT VIEW
OF THE CLIMATE SYSTEM
ON [DECADAL AND LONGER] TIMESCALES.
IN PRACTICE…
“ ”
Toby Ault
CLIVAR Exchanges/Past Global Changes Magazine, 2017

38. Source: Chase et al., Elements (2018)
THE ELDERFIELD CURVE OF HOW CONFIDENCE IN A GIVEN PROXY EVOLVES OVER TIME
old-fashioned
phase?

39. DENDROCLIMATOLOGY IS WELL-
ESTABLISHED BUT QUESTIONS
REMAIN ABOUT THE CLIMATE
CLUES ENCODED IN TREE RINGS
— PARTICULARLY AT DECADAL-
TO-CENTENNIAL TIMESCALES.

40. FIRST LAW
OF GEOGRAPHY

41. EVERYTHING IS RELATED
TO EVERYTHING ELSE,
BUT NEAR THINGS
ARE MORE RELATED
THAN DISTANT THINGS.
“ ”
Waldo Tobler
University of California, Santa Barbara

42. Widespread drought caused narrow rings
to form across the southwest USA
during 1748 and 1750.
Source: Kurt Kipfmueller, University of Minnesota

43. HOW DOES THE AGREEMENT
BETWEEN TREE-RING RECORDS
AT DECADAL FREQUENCIES
AND LONGER
VARY ACROSS SPACE AND TIME?
and what is a reasonable expectation
(null hypothesis) for that behavior?

44. SIGNAL-
FREE”
“

45. McPARTLAND
ET AL
TBD
DOES SIGNAL-FREE
DETRENDING
INCREASE CHRONOLOGY
COHERENCE IN LARGE
TREE-RING NETWORKS?

46. Signal-free detrending can
make tree-ring chronologies
more coherent with their
neighbors (➡), but in other
cases, it appears to introduce
low-frequency noise ( ).
Source: McPartland et al., Dendrochronologia (revision submi ed)
➡ ➡

47. IS IT POSSIBLE
TO IDENTIFY AN OPTIMAL DETRENDING
FOR THE RECOVERY OF
LOW-FREQUENCY PATTERNS
FROM TREE-RING NETWORKS OF VARIOUS
SIZES AND COMPOSITIONS?
and is it a good idea to do that?

48. PROCESS
MODELS

49. …ONE MAY MODEL
THE FORMATION OF THE RECORD
BY EXPLICITLY REPRESENTING
THE CHAIN OF PHYSICAL AND BIOLOGICAL PROCESSES
WHICH LIE BETWEEN
THE CLIMATIC INFORMATION
AND THE OBSERVED SIGNAL.
“ ”
Joël Guiot
Past Global Changes Magazine, 2017

50. DEE
ET AL
2017
IMPROVED SPECTRAL
COMPARISONS OF
PALEOCLIMATE MODELS
AND OBSERVATIONS VIA
PROXY SYSTEM MODELING:
IMPLICATIONS FOR MULTI-
DECADAL VARIABILITY

51. Source: Dee et al., Earth and Planetary Science Le ers (2017)
THE SPECTRA OF SYNTHETIC TREE-RING WIDTHS GENERATED BY PROCESS MODELS (GREEN LINE,
GRAY ERROR ESTIMATES) GENERALLY MATCH THE BEHAVIOR OF THE REAL DATA (BLACK LINE).

52. CAN WE USE PROCESS MODELS
TO CONSTRAIN
THE UPPER OR LOWER LIMITS OF
DECADAL-TO-CENTENNIAL
CLIMATE VARIABILITY
DURING THE PAST TWO MILLENNIUM?

53. Source: Kevin Anchukaitis, University of Arizona

55. @sco stgeorge