Kim M. Cobb @coralsncavesPamela Grothe, Hussein Sayani,

Alyssa Atwood, Tianran Chen, Intan Nurhati

Nick Hitt, Gemma O’Connor

Earth and Atmospheric Sciences, Georgia Tech

Samantha Stevenson, UCSB

Chris Charles, SIO, UCSD

Larry Edwards, Hai Cheng, UMN

Advances in paleo-ENSO:

a past to future perspective

Google Earth

Palmyra (6N, 162W)Fanning (4N, 160W)Christmas (2N,157W)

https://socialforecasting.files.wordpress.com/2015/08/el-nino-godzilla.jpg

2015/2016 El Niño

https://socialforecasting.files.wordpress.com/2015/08/el-nino-godzilla.jpg

1997/98 El Niño

Is ENSO changing?

How much has it varied in the past?

What has governed those variations?

living coral

last 50-100 yrs

“fossil” coral

last 7000 yrs

U/Th dated

drilled via SCUBA

storm/tsunami deposits

scattered on beaches

across the tropics

1mm sampling = monthly resolution

Coral d18O = SST + d18Oseawater

1mm sampling = monthly resolution

Coral d18O = SST + d18Oseawater

co-varies with SSS,

for the most part

Fairbanks et al.,1997

Schmidt, 1999

LeGrande & Schmidt, 2006

Conroy et al., 2014

during

El Niño

events

Feb 2016

OISST

Jan-Mar 2016

OLR

during

El Niño

events

Feb 2016

OISST

Jan-Mar 2016

OLR

warm SST drives

coral d18O down

rainy conditions

drive coral d18O down

SS

T (

ºC)

d1

8O

(‰

)

Christmas coral d18O vs. SST

grey=OISSTcolors=coral d18O

Evans et al., 1999Nurhati et al., 2009

Grothe et al., in prepO’Connor et al., in prepCoral d18O records are

interchangeable with SST.

On interannual timescales, SST drives ~80-90% of coral d18O variability.

plotting interannual coral d18O variability

over the last 7,000 years . . .

Grothe et al., under reviewCobb et al, 2013Cobb et al., 2003McGregor et al., 2013Grothe et al., in prepWoodroffe et al., 2003

Interannual variability over 7,000yrs

2°N-2°S temperature evolution in the Pacific : 2 simulations

6k

0k

PI

250 running mean 250 running mean

Departure from 250 running mean

from Pascale Braconnot, IPSL

Grothe et al., under reviewCobb et al, 2013Cobb et al., 2003McGregor et al., 2013Grothe et al., in prepWoodroffe et al., 2003

Is late 20th century ENSO variability

stronger than the pre-industrial?

Null hypothesis: observed distribution reflects sub-

samples from a highly variable, yet stationary, system

Null hypothesis: observed distribution reflects sub-

samples from a highly variable, yet stationary, system

1) Linear Inverse Model – 20,000yrs of NIÑO3.4

(Capotondi & Shardeshmukh, 2017)

2) Last Millennium Ensemble – 10 x 1000yrs of

NIÑO3.4

(Otto-Bleisner et al., 2016)

Grothe et al., In review

Interannual coral d18O is stronger

in last 50yrs vs pre-industrial period

20,000yrs

statistical model10,000yrs

dynamical model

Difference in std dev Difference in std dev

Additional paleo-evidence for a recent

strengthening of El Niño variability:

Li et al., 2013 multi-proxy incl Java tree rings

McGregor et al., 2013 Pacific multi-proxy

Liu et al., 2017 Taiwan tree d18O

Cobb et al., 2013; Grothe et al., under review

Line Islands coral d18O

Three explanations for observed intensification:

ENSO SST variance higher in central equatorial Pacific

(Yeh et al., 2009; others)

ENSO SST variance higher overall

(Cai et al., in press)

“More rainfall bang for our SST buck” – ENSO

hydrological impacts larger in a warming world

(Power et al., 2013; Cai et al., 2014)

Three explanations for observed intensification:

ENSO SST variance higher in central equatorial Pacific

(Yeh et al., 2009; others)

ENSO SST variance higher overall

(Cai et al., in press)

“More rainfall bang for our SST buck” – ENSO

hydrological impacts larger in a warming world

(Power et al., 2013; Cai et al., 2014)

Coral d18O ensembles of major El Niño events:

SST vs hydrological contributions?

Gemma O’Connor et al., in prep

grey = SST

colors = coral d18O1997/98

2015/16

O’Connor et al., in prep

O’Connor et al., in prep

2015/2016 coral d18O

80% SST,

20% seawater d18O

coral d18O

SST

SSS

seawater d18O

1997/98 2015/16

Isotope-enabled

models link

dynamics of

ocean and

atmosphere

to seawater

d18O variability

e.g. isoROMS

(Stevenson et

al., 2018)

Nicholas Hitt et al., in prep

1950 1960 1970 1980 1990 2000 2010Time (Yr)

-5.6

-5.2

-4.8

-4.4

-41

8O

24

26

28

30

SS

T (°C

)

1985 +/- 3

1996 +/- 22002 +/- 2

1992 +/- 21962 +/- 2 1971 +/- 2

1952 +/- 2

1890 1892 1894 1896 1898

-5.6

-5.2

-4.8

-4.4

-4

18O

1898 +/- 2

1914 1916 1918 1920 1922

Time (Yr)

1919 +/- 3

1923 1925 1927

1930 +/- 2

1929 1931 1933 1935 1937 1939

1934 +/- 2

Goal: continuous reconstruction over last 200+yrs

Collecting,dating,analyzingyound fossil corals

Summary

- empirical evidence that ENSO variability is already

stronger (up to 30%) than pre-industrial

- new reconstructions allow us to address

interannual & decadal-to-centennial-scale

variability at monthly resolution over the last 200yrs

- complements rich archive of last millennium

data and Holocene data (data—model comparison)

Summary

- empirical evidence that ENSO variability is already

stronger (up to 30%) than pre-industrial

- new reconstructions allow us to address

interannual & decadal-to-centennial-scale

variability at monthly resolution over the last 200yrs

- complements rich archive of last millennium

data and Holocene data (data—model comparison)

BEFORE AFTER

This time, it’s personal.

10 months of bleaching-level

thermal stress 85% of reef killed

recovery will take decades, but . . .

Isn’t it ironic?

Some simple math

In 2017, I flew 110,000 miles = 18,000 lbs CO2

My total CO2 footprint in 2017 = 25,000 lbs CO2

Average American = 40,000 lbs CO2/yr

Average Ecuadorian = 6,200 lbs CO2/yr

Some simple math

In 2017, I flew 110,000 miles = 18,000 lbs CO2

My total CO2 footprint in 2017 = 25,000 lbs CO2

Average American = 40,000 lbs CO2/yr

Average Ecuadorian = 6,200 lbs CO2/yr

ENSO2018 speakers & program committee =

220,000 lbs

GLOBAL WARMING OF 1.5 °C an IPCC special report on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty

Summary for Policymakers This Summary for Policymakers was formally approved at the First Joint Session of Working Groups I, II and III of the IPCC and accepted by the 48th Session of the IPCC, Incheon, Republic of Korea, 6 October 2018.

SUBJECT TO COPY EDIT

- aggressively reduce emissions now

- requires large-scale cultural shift

- natural carbon sequestration is key

My commitment

fly

Tell me what you think

Inform student projects

http://pollev.com/kimcobb971

The Third Millennium Alliance. http://tmalliance.org

Paypal to

kcobb@eas.gatech.edu

Your carbon offset

matched for TODAY only!

suggestion:

$25 for domestic flight

$50 for all others

http://pollev.com/kimcobb971

Dee et al., in prep

(all tropical eruptions)

a. R adiative forcing < 0W /m 2, n=20 b. R adiative forcing < -15W /m 2, n=3

(1257 Sam alas only)

c. R adiative forcing < -30W /m 2, n=1-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-6 -4 -2 E rup +2 +4 +6 -6 -4 -2 E rup +2 +4 +6 -6 -4 -2 E rup +2 +4 +6

M C A P erm utation Test, 95% C I

La N iña-like (+ δ18O anom alies)

E l N iño-like ( - δ18O anom alies)

E ruption Year

Figure 4:Superposed E poch A nalysis for Volcanic Forcing.The figure show s com posite coralδ18O response forthe 5 years before and 5 years follow ing stacked eruptions fordifferentforcingthresholds (and see SIFig. 3). a. 0 W /m 2 (alltropicaleruptions),b. -15 W /m 2,c. -30 W /m 2

(Sam alas only).A llD ata B andpass Filtered at2-7 Years,and C oralTim e A xis +1.W e perform eda M onte C arlo resam pling test,and the 1000 realizations of the data are show n in grey. A re-sponse exceeding the grey error w indow suggests a non-random result. 11-year w indow s of thePalm yra δ18O data,centered aboutvolcanic eruptions w ith varying forcing thresholds. D ata hasbeen norm alized and stacked.R ed barsindicate an ElN ĩno-like response,and blue barsindicate aLa N ĩna-like response.G ray shaded area show sthe 2.5% and 97.5% confidence intervalsfor1000M onte C arlo random sam plings ofthe data,indicating thatthe coralresponse to volcanic forcingis notsignificant. Shifting earlier coralpieces forw ard (C t+1) 1 year results in a significant ElN ĩno-like response in the EN SO -bandpass filtered data atYear0 (eruption year).

14

(all tropical eruptions)

a. R adiative forcing < 0W /m 2, n=20 b. R adiative forcing < -15W /m 2, n=3

(1257 Sam alas only)

c. R adiative forcing < -30W /m 2, n=1-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-6 -4 -2 E rup +2 +4 +6 -6 -4 -2 E rup +2 +4 +6 -6 -4 -2 E rup +2 +4 +6

M C A P erm utation Test, 95% C I

La N iña-like (+ δ18O anom alies)

E l N iño-like ( - δ18O anom alies)

E ruption Year

Figure 4:Superposed E poch A nalysis for Volcanic Forcing.The figure show s com posite coralδ18O response forthe 5 years before and 5 years follow ing stacked eruptions fordifferentforcingthresholds (and see SIFig. 3). a. 0 W /m 2 (alltropicaleruptions),b. -15 W /m 2,c. -30 W /m 2

(Sam alas only).A llD ata B andpass Filtered at2-7 Years,and C oralTim e A xis +1.W e perform eda M onte C arlo resam pling test,and the 1000 realizations of the data are show n in grey. A re-sponse exceeding the grey error w indow suggests a non-random result. 11-year w indow s of thePalm yra δ18O data,centered aboutvolcanic eruptions w ith varying forcing thresholds. D ata hasbeen norm alized and stacked.R ed barsindicate an ElN ĩno-like response,and blue barsindicate aLa N ĩna-like response.G ray shaded area show sthe 2.5% and 97.5% confidence intervalsfor1000M onte C arlo random sam plings ofthe data,indicating thatthe coralresponse to volcanic forcingis notsignificant. Shifting earlier coralpieces forw ard (C t+1) 1 year results in a significant ElN ĩno-like response in the EN SO -bandpass filtered data atYear0 (eruption year).

14