As the world warms: coral records of climate change

Kim CobbEAS, Georgia Inst. of Technology

AcknowledgementsLab members:Intan Suci NurhatiJulien Emile-GeayLaura ZaunbrecherJames HerrinHussein SayaniEAS undergrads

Chris CharlesScripps Inst of Oceanography

Larry Edwards, Hai ChengUniversity of Minnesota

with special thanks to:Norwegian Cruise LinesPalmyra Research ConsortiumSarawak Department of Forestry, MalaysiaNOAA, NSF

Which of the following are scientific statements?

1) Reducing CO2 emissions would hurt the economy.

2) Improved technology is the best way to slow globalwarming.

3) A warming of 1ºC over the next 50yrs is dangerous.

4) Global temperatures were 5ºC colder during the LastGlacial Maximum.

5) Hurricane Katrina was caused by global warming.

Which of the following are scientific statements?

1) Reducing CO2 emissions would hurt the economy.

2) Improved technology is the best way to slow globalwarming.

3) A warming of 1ºC over the next 50yrs is dangerous.

4) Global temperatures were 5ºC colder during the LastGlacial Maximum.

5) Hurricane Katrina was caused by global warming.

Why do 99.999% of climate scientists believe that CO2 is warming the planet?

1. Theory predicts that increasing atmospheric CO2 should warm the planet.

2. Geologic evidence links CO2 and temperature in the past.

3. The warming is unprecedented in the most recent centuries (dwarfs natural variability).

4. Climate models show that rising CO2 is necessary to simulate20th century temperature trends (solar and volcanic minor players).

Ice core climate and CO2 records

tiny gas bubbles in the ice trapancient air samples

Atmospheric CO2 and temperature over the past 650 thousand years

CO2 and temperatureare closely linkedon geologic timescales

#2

To understand how climate has changed in the past, we need to use records of climate preserved in ice cores, ancient tree rings, coral bands, and other “paleoclimatic” sources:

key is to CALIBRATE to temperature records

The “Hockey Stick”

Key Points:error bars increase as you go back in timenatural variability accounts for <0.5ºC over the last millenniumlate 20th century temperature trend is unprecedented

#3

IntergovernmentalPanel onClimate Change(IPCC) 2001

#4

Solar and volcanic only anthropogenic only

natural & anthropogenic

The uncertain climate futureRange of scenarios:Strict international agreements CO2 at 600ppm by 2100 *390ppm todayMid-ground 850ppm by 2100 280ppm 1800Business as usual 1550ppm by 2100

IPCC AR4, 2007

but we need to know about regional climate changes, and specifically

about regional precipitation changes

white = models disagreecolor = models mostly agreestippled = models agree

IPCC AR4, 2007

Research Goal: constrain tropical Pacific response to anthropogenic global warming

Approach: reconstruct tropical Pacific climate at high-resolution forthe last millennium

Dai and Wigley, 2000

El Niño Temperature

El Niño Precipitation

WHY?

“El Niño-Southern Oscillation”(ENSO)

ENSO is a climate pattern in thetropical Pacific which arisesfrom coupled interactions betweenthe atmosphere and ocean

ENSO impacts global climate every2-7 years (huge impact on rainfall)

Tropical Pacific climate variabilityover decades to centuries to millennia poorly constrained

Tropical Pacific climate and global warming

ENSO std in control runENSO std ObservedENSO std in GHG run

El NiñoLa Niña

Collins et al., 2004

Timmermann et al., 1999

Cane et al., 1997

We don’t know how the tropical Pacific will respond to global warming, if at all.

Studies are contradictory because:1) climate data are scarce prior to

19502) climate models do not simulate

ENSOaccurately

more El Niño’s

more La Niña-like

both

Research Questions

How has the tropical Pacific climate system responded to CO2 forcing?

What aspects of present tropical Pacific climate are unprecedented?

compare last several decades to recent centuries

Fanning2005-?

Palmyra1997-?

Christmas1998-?

Corals: The geologic record of El Niño

CORALS from the tropical Pacific record El Niño’s in the geochemistry of their skeletons

Living Porites corals provide recordsfor the last 200 years

Fossil Porites corals enable us to extend the record back many centuries

Generating climate reconstructions from the Palmyra corals:

1) Recover the corals, both modern (~10) and fossil (~100).

2) Prove that the coral geochemistry tracks large-scale climate.ie. Calibrate the modern coral record against the instrumental record of climate.

3) Apply geochemistry to fossil corals and date them (U/Th dating).

Aerial view of Palmyra

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Date (A.D.)

Modern

The Palmyra Island Coral Collection

Little Ice Age (LIA)canals frozen in Europe

Medieval Warm Period (MWP)Greenland green

SS

T A

nom

oly

(°C

)

3

2

1

0

-1

-2

18 O

(‰

)

-0.6

-0.4

-0.2

0.0

0.2

NIÑO3.4 SSTPalmyra coral

Year (A.D.)

1900 1920 1940 1960 1980 2000

SS

T A

nom

oly

(°C

) 1

0

-1

-2

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

R = -0.66

R = -0.84

18 O

(‰

)

Palmyra coral oxygen isotopes vs. tropical Pacific SST

Overlapping fossil corals: ancient El Niño events

Good reproducibility between coral geochemical recordsincreases confidence in coral climate reconstructions.

A millennium-long reconstruction of tropical Pacific temperature

Key climate observations:1) late 20th century warming is unprecedented in the last millennium2) no cooling during the Northern Hemisphere’s “Little Ice Age”3) significant cooling implied during the NH’s “Medieval Warm Period”

Conclusions-paleoclimate data have an important role to play in

global climate research

- corals provide quantitative reconstructions of temperature

- evidence for ongoing tropical Pacific climate change that could shape future global temperature and precipitation patterns

A climate scientist’s plea:

Get your climate information from a climate scientist (not the media, politicians, etc)

Use flourescent light bulbs, don’t drive SUVs, a

The Earth’s ice is melting,sea level has increased~3 inches since 1960~1 inch since 1993

-signs of accelerating melting are now clear

-land ice particularly striking, poles more complicated

-IPCC estimates project current trends forward i.e. LOWER estimateusing no acceleration

The uncertain sea level future

Stroeve et al, 2008

Sea level rise:IPCC says 7” to 22” by 2100,much more if rapid ice sheet collapse occurs

most scientists would go on record for 1m rise (30 inches)

Projected temperature change: global view

Take-homes:-poles warm more

-land warms more

-ocean warming patchy and complex

uneven warmingwill shift rainfall patterns

Diffenbaugh et al, 2005

UShttp://www.usgcrp.gov/usgcrp/nacc/se-mega-region.htm

Regional models use global model output,run at high-resolution (5km) grid

Length of heat waves increase(# days/event)

Peak temperatures increase

white = models disagreecolor = models mostly agreestippled = models agree

Projecting precipitation is VERY uncertain business,yet extremely critical to human impacts.

Projected precipitation change: global view

Projected precipitation change: regional view

change in yearlyaverage precipitation # heavy rain days # dry days

Diffenbaugh et al, 2005

mm/day days/yr days/yr

IPCC says increasein hurricane intensity“likely” (66%)

CERTAIN

UNCERTAIN

Warming of 1-6°C by 2100.

Sea levels will rise by 6 to 30 inches by 2100.

Precipitation patterns will change. More erratic precipitation.

Extreme events will increase, hurricanes more intense.

Prospect of abrupt climate change.

What is a country to do?

There are only three (prudent) options:

1)use less energy- drive less, drive smaller (plug-in?) cars- conserve electricity- recycle, reuse

2) make “clean” energy- solar power, wind power, nuclear energy

3) take CO2 out of the sky (much more difficult)

…. but how much at what cost?

Some clear lessons:

1) efficiency makes $$

2)gains from cellulosic biofuels likely (notcorn ethanol!)

3) taking CO2 out of the sky is more costly thannot putting it in the atmosphere to begin with

My homepage: http://shadow.eas.gatech.edu/~kcobb

Scientific Summary

Strong evidence supports the idea that anthropogenic CO2 is warming the planet.

Future climate changes in a warming environment are still uncertain, although:

-sea level rise certain (but how much by when?, ~1m starting point)

- SE precipitation will become more erratic (water resource management)

-prospect for increasing hurricane activity

A Climate Scientist’s Plea

Evaluate the scientific evidence for yourselves, from a scientific source.

Distinguish between the science of global warming and the politics/economicsof global warming.