Even after more than a century of coordinated monitoring, instrumental weather observations are still too short to adequately constrain decadal or multidecadal behavior in the Earth’s climate system. Leading climatologists and climate modelers have called for the wider application of high-resolution proxy records to decadal variability and prediction studies, and our community has responded by producing new paleoclimate products that specifically target this type of ‘intermediate-term’ behavior. But we now also know our medium changes that message: the biological and geological systems that encode climate information into natural archives often also alter the original ‘input’, usually due to either seasonal filtering or non-climatic persistence. In this talk, we’ll discuss some of the challenges inherent to the use of high-resolution proxies to study decadal or multi-decadal climate variability, and suggest strategies that might clarify how climate acts on those timescales. And we’ll also present a new theoretical framework that could help paleo-scientists evaluate competing ideas about the causes of decadal- or multi-decadal events known to have occurred during the past one or two millennia.

1. DISENTANGLING
THE DECADAL ‘KNOT’
IN HIGH-RESOLUTION PALEOCLIMATOLOGY
SCOTT ST. GEORGE TOBY AULT MARA McPARTLAND
Second International TERENO Conference | Berlin, Germany | October 10, 2018

2. LONG
TERM

4. Source: Estes et al., Nature Ecology and Evolution, 2018
MOST OBSERVATIONAL STUDIES IN ECOLOGY BASED ON AUTOMATED SENSORS (A), REMOTE
SENSING (R), OR FIELD STUDIES (F) ARE CONDUCTED OVER A FEW YEARS OR LESS.

6. Source: LACCORE, University of Minnesota

8. WHAT IS THERE TO BE GAINED
BY LOOKING INTO THE PAST?

9. SLOWALIENRARE

10. HIGH-RESOLUTION BI0- AND GEO-ARCHIVES
CAN HELP SHED LIGHT ON DECADAL PHENOMENON
AND THEIR UNDERLYING PROCESSES…
…BUT THESE APPLICATIONS REQUIRE US TO ADDRESS
SEVERAL CHALLENGES INVOLVED WITH RECOVERING
’SLOW’ CLIMATE SIGNALS FROM NATURAL RECORDERS.

12. MITCHELL
1976

13. CLIMATE
IS NOW RECOGNIZED
AS BEING CONTINUOUSLY VARIABLE,
ON ALL SCALES OF TIME.
“ ”
J. Murray Mitchell
Quaternary Research, 1976

14. Source: Huybers and Curry, Nature, 2006

15. … THE CENTURY-LONG SPAN
OF TYPICAL CLIMATE CHANGE PROJECTIONS
DOES NOT FIT
THE DECADAL OUTLOOK
OF RESOURCE MANAGERS
AND THOSE PLANNING INFRASTRUCTURE INVESTMENTS.
“ ”
Mark Cane
Nature Geoscience, 2010

16. MANDELBROT
WALLIS
1968

18. WE SHALL SPEAK OF
“JOSEPH-WILD” BEHAVIOR
WHEN
THE WETTEST DECADE
WITHIN A CENTURY INCLUDES
AN EXTRAORDINARY “TERM”
OF WET YEARS.
“ ”
Benoit Mandelbrot and James Wallis
Water Resources Research, 1968

19. DECADAL/
MULTI-DECADAL
VARIABILITY

21. 1900 1920 1940 1960 1980 2000
-3
-2
-1
0
1
2
3
cm/month
SINCE THE BEGINNING OF THE 20TH CENTURY,
THE SAHEL REGION HAS EXPERIENCED SEVERAL DECADAL OR MULTIDECADAL ‘RUNS’
OF PERSISTENTLY HIGH OR LOW RAINY SEASON PRECIPITATION.
Source: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington

23. Source: Ault, T. R., & St George, S. (2010). The magnitude of decadal and multidecadal variability in North American precipitation. Journal of Climate, 842–850.
STRONG DECADAL VARIABILITY IN WINTERTIME CLIMATE HAS CAUSED
RAINFALL, RIVER FLOW, AND EXTREME FLOODS IN NORTHERN CALIFORNIA
TO BE HIGHLY SYNCHRONIZED SINCE THE 1930s.

24. COLORADO RIVER
Source: Ralph Earlandson

25. THE COLORADO RIVER PROVIDES WATER TO 40 MILLION PEOPLE,
BUT YEARLY FLOWS HAVE BEEN BELOW THE LEGAL ALLOCATION
FOR MOST OF THE PAST TWO DECADES.
Source: United States Bureau of Reclamation, Lower Colorado region
1920 1940 1960 1980 2000
5x106
107
1.5x107
2x107
acre-feet/yr

27. INSTRUMENTAL CLIMATE
OBSERVATIONS
MODEL SIMULATIONS

28. … 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]…
“ ”
Vikram Mehta et al., 2011
Bulletin of the American Meteorological Society

30. Source: Dan Griffen
1DECADAL EVENTS IN TERRESTRIAL SYSTEMS

31. Sources: Cook et al. (2004). Long-term aridity changes in the western United States. Science 306:1015–1018; Cook et al., (2016),
North American megadroughts in the Common Era: reconstructions and simulations. WIREs Climate Change, 7:411–432 .
DURING THE 11TH CENTURY, MORE THAN 40% OF THE WESTERN UNITED STATES
EXPERIENCED DROUGHT, EVEN WHEN AVERAGED OVER SEVERAL DECADES.

32. Source: Balanzategui, Daniel, et al., An 810-year history of cold season temperature variability for northern Poland. Boreas 47.2 (2018): 443-453.
THE 800-YR WINTER TEMPERATURE RECONSTRUCTION PRODUCED BY
THE GFZ TREE-RING LABORATORY INCLUDES SEVERAL PROLONGED RUNS
OF EXTREME COLD OR WARM YEARS IN NORTHERN POLAND.

33. 2EXTENDED RECORDS OF DECADAL CLIMATE MODES

34. Source: MacDonald, G. M., & Case, R. (2005). Variations in the Pacific Decadal Oscillation over the past millennium. Geophysical Research Le ers.
HIGH-RESOLUTION PROXIES HAVE BEEN USED TO PRODUCE MULTI-CENTURY LONG
ESTIMATES OF LEADING DECADAL CLIMATE MODES SUCH AS THE PDO.

36. KEITH BRIFFA

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

38. SIGNAL FIDELITY

39. DAW06
DAR01
BIO01
MAC05
G&S01
1700 1750 1800 1850 1900 1950 2000
Source: Kipfmueller, K. F., Larson, E. R., & St George, S. (2012). Does proxy uncertainty affect the relations inferred between the Pacific Decadal
Oscillation and wildfire activity in the western United States? Geophysical Research Le ers, 39(4), L04703.
INDEPENDENT PROXY ESTIMATES OF THE PACIFIC DECADAL OSCILLATION INDEX
DO NOT AGREE WITH EACH OTHER DURING THE 18TH AND 19TH CENTURIES.
PDO Positive (white) | PDO Negative (black)

40. AS IT STANDS,
THE CURRENT DISAGREEMENT
AMONG THE EXISTING PDO RECONSTRUCTIONS
IS PROBLEMATIC
FOR ANY ASSESSMENT
OF PDO VARIABILITY
AND PDO-RELATED IMPACTS
OVER THE LAST SEVERAL HUNDRED YEARS.
“ ”
Ma hew Newman et al., 2016
Journal of Climate

41. SIGNAL DISTORTION

42. MARSHALL McLUHAN

43. BIOLOGY

44. MATALAS
1962

45. 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.
“ ”
Nicholas Matalas, 1962
International Association of Scientific Hydrology Bulletin

46. STORAGE

47. HUYBERS
ET AL
2015

48. Source: Huybers, K., Rupper, S., & Roe, G. H. (2015). Response of closed basin lakes to interannual climate variability. Climate Dynamics, 1–15.
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.

49. WE FIND THAT
INTERANNUAL CLIMATE VARIABILITY ALONE
CAN EXPLAIN MUCH OF THE
DECADAL-TO-CENTENNIAL VARIATIONS
IN THE LAKE-LEVEL RECORD.
“ ”
Kathleen Huybers et al., 2015
Climate Dynamics

50. DECADAL
“KNOT”

52. PROGRESS ON THE INTERPRETATION OF
OCEAN-LAND CONNECTIVITY
WOULD GAIN FROM
STUDYING THE RELATIONSHIP
BETWEEN LAND (E.G., TREE RINGS)
AND OCEAN PROXIES (E.G., CORALS AND SHELLS).
“ ”
Christophe Cassou et al.
Bulletin of the American Meteorological Society, 2018

53. IIMPROVING ACCESS
TO GLOBAL MULTIPROXY NETWORKS

56. Sources: Emile-Geay, J., Mckay, N. P., Kaufman, D. S., Gunten, Von, L., Wang, J., Anchukaitis, K. J., et al. (2017). Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era. Scientific Data, 4, 1–33.
Map created by Lara Klippel, Johannes Gutenberg University
THE PAGES 2K CONSORTIUM HAS RELEASED A GLOBAL DATASET WITH
MORE THAN 690 TEMPERATURE-SENSITIVE PROXIES SPANNING THE COMMON ERA.

57. CORAL-HYDRO2K
MULTICHRON
Constraining modeled multidecadal climate variability
in the Atlantic using proxies derived from marine
bivalve shells and coralline algae
Tropical ocean hydroclimate and temperature
from coral archives

58. IIADOPTING A “MORE NUANCED” APPROACH
TO DECADAL CLIMATE MODES

59. PACIFIC
DECADAL
OSCILLATION

60. Source: Newman, M., Alexander, M. A., Ault, T. R., Cobb, K. M., Deser, C., Di Lorenzo, E., et al. (2016). The Pacific Decadal Oscillation, Revisited. Journal of Climate, 29(12), 4399–4427.

61. A MORE NUANCED APPROACH
THAT TARGETS ONE OR MORE
OF THE DIFFERENT PROCESSES
THAT CONTRIBUTE TO PDO-RELATED VARIABILITY
WOULD LIKELY LEAD TO AN UNDERSTANDING
ABOUT HOW SUCH PROCESSES HAVE VARIED IN THE PAST,
AND THEIR POTENTIAL INTERRELATIONSHIPS.
“ ”
Ma hew Newman et al.
Journal of Climate, 2016

62. IIISUPPORTING PALEOCLIMATE INTERPRETATION
VIA EXPLICIT HYPOTHESIS TESTING

63. Source: Cook et al., 2014: Pan-continental droughts in North America over the last millennium. Journal of Climate, 27, 383–397.
HIGH-RESOLUTION PROXIES OFTEN FEATURE DECADAL OR MULTIDECADAL EVENTS,
BUT IT’S NOT CLEAR WHETHER LONG-LASTING CLIMATE EXCURSIONS ARE THE
PRODUCT OF UNUSUAL EXTERNAL FORCINGS.

64. INTERANNUAL VARIABILITY
+ TIME
OUT-OF-SAMPLE
CLIMATE STATES

65. NULL HYPOTHESISThe characteristics of megadrought in the western US (as reconstructed by
tree rings) are consistent with those arising from a stochastically forced,
linearly damped system with stationary statistics.

66. Drought Area Index (%)
Source: Ault, T. R., St George, S., Smerdon, J. E., Coats, S., Mankin, J. S., Carrillo, C. M., et al. (2018). A robust null hypothesis for the potential causes of megadrought in western North America. Journal of Climate, 31(1), 3–24.
EVEN WHEN STATISTICAL MODELS ARE CONDITIONED ON CLIMATE DATA FROM THE
LATE 20TH CENTURY (ONLY), THEY STILL PRODUCE SYNTHETIC MEGADROUGHTS
WHEN ALLOWED TO RUN FOR A MILLENNIUM.

67. 1000YEARS

68. DECADAL/
MULTI-DECADAL
VARIABILITY

69. THE FAMINE STELA
Source: WIkipedia User Morburre

70. GILGAMESH AND THE BULL OF HEAVEN

71. JOSEPH INTERPRETING PHARAOH'S DREAM

72. PROXY ARCHIVES

73. HIGH-RESOLUTION BI0- AND GEO-ARCHIVES
CAN HELP SHED LIGHT ON DECADAL PHENOMENON
AND THEIR UNDERLYING PROCESSES…
…BUT THESE APPLICATIONS REQUIRE US TO ADDRESS
SEVERAL CHALLENGES INVOLVED WITH RECOVERING
’SLOW’ CLIMATE SIGNALS FROM NATURAL RECORDERS.

74. @sco stgeorge