Plenary talk by Kim Cobb at the 2016 CLIVAR Open Science Meeting, in Qingdao, China. http://www.clivar2016.org

1. Paleo-constraints on
future tropical Pacific
climate
Kim M. Cobb
Pamela Grothe, Hussein Sayani,
Alyssa Atwood, Tianran Chen, Intan Nurhati
Earth and Atmospheric Sciences, Georgia Tech
Chris Charles, SIO, UCSD
Larry Edwards, Hai Cheng, UMN
•
Paleoclimate
Research •
GeorgiaTech
•
Cobb Lab

2. Google Earth

3. Google Earth

4. NOAA
November, 1997

5. https://socialforecasting.files.wordpress.com/2015/08/el-nino-godzilla.jpg
2015/2016 El Niño

6. ERSSTv4
1880 1900 1920 1940 1960 1980 2000
Year
-2
-1
0
1
2
3
NINO3.4SST(°
C)
Is ENSO changing?

7. ERSSTv4
1880 1900 1920 1940 1960 1980 2000
Year
-2
-1
0
1
2
3
NINO3.4SST(°
C)
Is ENSO changing?

8. Option 1
Wait 100+ years until we have enough instrumental data
(e.g. Stevenson et al., 2012)
Is ENSO changing?

9. Option 1
Wait 100+ years until we have enough instrumental data
(e.g. Stevenson et al., 2012)
Option 2
Use paleo-ENSO records to establish quantitative estimates of
pre-industrial ENSO variability, compare to recent ENSO variability
Is ENSO changing?

10. last 100+ yrs
last 7000 yrs
U/Th dated
drilled via SCUBA
storm/tsunami deposits
scattered on beaches
across the tropics

11. 1mm sampling transect for
coral oxygen isotopes (δ18O)
affords monthly resolution
Coral δ18O = SST + δ18Oseawater

12. 1mm sampling transect for
coral oxygen isotopes (δ18O)
affords monthly resolution
Coral δ18O = SST + δ18Oseawater
co-varies with SSS
(Fairbanks et al., 1997;
Conroy et al., 2014)

13. Feb 2016
OISST
Jan-Mar 2016
OLR
warm SST drives coral δ18O down
rainy conditions
drive coral δ18O down

14. 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
-5.5
-5
-4.5
-4
22
24
26
28
30
Nurhati09 Evans99 x126 x123 Minicore1 Minicore2 OISSTv2
SST(ºC)
δ18O(‰)
coral oxygen isotopes vs. SST
grey=OISST
colors=coral δ18O
Evans et al., 1999
Nurhati et al., 2009
Grothe et al., in prep
O’Connor et al., in prep

15. 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
-5.5
-5
-4.5
-4
22
24
26
28
30
Nurhati09 Evans99 x126 x123 Minicore1 Minicore2 OISSTv2
SST(ºC)
δ18O(‰)
coral oxygen isotopes vs. SST
grey=OISST
colors=coral δ18O
Evans et al., 1999
Nurhati et al., 2009
Grothe et al., in prep
O’Connor et al., in prepCoral δ18O records are
interchangeable with SST.
Replication yields better reconstruction.

16. 800 1000 1200 1400 1600 1800 2000
−5.5
−5
−4.5
−4
Year CE
Xmas coral d18O last millennium
monthly coral δ18O records
through the last millennium
2015/2016 El Niño
δ18O(‰)

17. 800 1000 1200 1400 1600 1800 2000
−5.5
−5
−4.5
−4
Year CE
Xmas coral d18O last millennium
monthly coral δ18O records
through the last millennium
2015/2016 El Niño
δ18O(‰)
Has ENSO variance changed?

18. 01000200030004000500060007000
−60
−40
−20
0
20
40
Year BP
ChangeinstdevofENSO(%)
Fanning
Christmas
Palmyra
20th century
range
Grothe et al., in prep
Cobb et al, 2013
Cobb et al., 2003
McGregor et al., 2013
Grothe et al., in prep
Woodroffeet al., 2003
1985-2005 ENSO variability
ENSO variance over the last 7,000yrs
stronger ENSO
weaker ENSO
Most pre-industrial data reflect
much weaker ENSO than present.

19. Virtually certain* that observed distribution of
interannual coral δ18O variance does not
reflect a stationary process.
* Significant of pre-industrial to modern shift in coral interannual variance is somewhat sensitive to the choice of null, and different
testing periods will give you slightly different significance levels. Full investigation of significance will be reported in Grothe et al., in
prep

20. Virtually certain* that observed distribution of
interannual coral δ18O variance does not
reflect a stationary process.
In and of itself, this does not prove that ENSO
has intensified with anthropogenic climate change.
* Significant of pre-industrial to modern shift in coral interannual variance is somewhat sensitive to the choice of null, and different
testing periods will give you slightly different significance levels. Full investigation of significance will be reported in Grothe et al., in
prep

21. Virtually certain* that observed distribution of
interannual coral δ18O variance does not
reflect a stationary process.
In and of itself, this does not prove that ENSO
has intensified with anthropogenic climate change.
However…
* Significant of pre-industrial to modern shift in coral interannual variance is somewhat sensitive to the choice of null, and different
testing periods will give you slightly different significance levels. Full investigation of significance will be reported in Grothe et al., in
prep

22. Evidence that (late) 20th century interannual
variance is stronger than pre-industrial values:
Li et al., 2013 à tree rings from Java
McGregor et al., 2013 à Pacific multi-proxy
Liu et al., in revision à Taiwan tree δ18O
Cobb et al., 2013; Grothe et al., in prep à
Line Islands coral δ18O

23. All paleo-ENSO records rely (to
varying extents) on hydrological
response to ENSO SST anomalies.
So now we have a new question:
Is ENSO SST variance already increasing?
or
Are we already seeing
“more rainfall bang for our SST anomaly buck”
that models project for the 21st century?
(Power et al., 2013; Cai et al., 2014)

24. BEFORE AFTER
link

25. Frontiers and opportunities
paleo-data assimilation
nal of Geophysical Research: Atmospheres 10.1002/2016JD024751
Figure 1. Conceptual framework for the Last Millennium Reanalysis, outlining our paleoassimilation approach. Starting
from the prior (a collection of simulated climate states) from which random draws are pulled, the states are mapped
Hakim et al.,
JGR-Atm, 2016

26. Past trips:
Aug 2014
March 2015
July 2015
Nov 2015
April 2016
Team:
Kim Cobb (Georgia Tech, paleoclimate)
Julia Baum (U. Victoria, ecologist)
Ruth Gates (UH, coral ecologist)
Mark Merrifield (UH, phys. oceanography)
Brian Powell (UH, phys. oceanography)
Samantha Stevenson (NOAA, climate
scientist, ocean modeler)
Planned trips:
Nov 2016
April 2017
Research Goals:
data assimilation of coral δ18O data
(iso-ROMS) à reanalysis products
integrated climate and ecological impact
study over 2015/16 El Niño and beyond
Frontiers and opportunities

27. Summary
The paleoclimate community needs CLIVAR
to unlock the vast potential of their data.

28. Summary
The paleoclimate community needs CLIVAR
to unlock the vast potential of their data.
CLIVAR needs the paleoclimate community
to address some of the most pressing
questions concerning the impacts of
anthropogenic climate change.

29. Summary
The paleoclimate community needs CLIVAR
to unlock the vast potential of their data.
CLIVAR needs the paleoclimate community
to address some of the most pressing
questions concerning the impacts of
anthropogenic climate change.
Rapid progress is possible but requires
interdisciplinary teams of scientists
working towards shared goals.