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As the world warms: coral records of climate change. Kim Cobb EAS, Georgia Inst. of Technology Acknowledgements Lab members: Intan Suci Nurhati Julien Emile-Geay Laura Zaunbrecher James Herrin Hussein Sayani EAS undergrads Chris Charles Scripps Inst of Oceanography

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slide1

As the world warms: coral records of climate change

Kim Cobb

EAS, Georgia Inst. of Technology

Acknowledgements

Lab members:

Intan Suci Nurhati

Julien Emile-Geay

Laura Zaunbrecher

James Herrin

Hussein Sayani

EAS undergrads

Chris Charles

Scripps Inst of Oceanography

Larry Edwards, Hai Cheng

University of Minnesota

with special thanks to:

Norwegian Cruise Lines

Palmyra Research Consortium

Sarawak Department of Forestry, Malaysia

NOAA, NSF

slide2

Which of the following are scientific statements?

  • Reducing CO2 emissions would hurt the economy.
  • 2) Improved technology is the best way to slow global
  • warming.
  • 3) A warming of 1ºC over the next 50yrs is dangerous.
  • 4) Global temperatures were 5ºC colder during the Last
  • Glacial Maximum.
  • 5) Hurricane Katrina was caused by global warming.
slide3

Which of the following are scientific statements?

  • Reducing CO2 emissions would hurt the economy.
  • 2) Improved technology is the best way to slow global
  • warming.
  • 3) A warming of 1ºC over the next 50yrs is dangerous.
  • 4) Global temperatures were 5ºC colder during the Last
  • Glacial Maximum.
  • 5) Hurricane Katrina was caused by global warming.
slide4

Why do 99.999% of climate scientists believe

that CO2 is warming the planet?

  • Theory predicts that increasing atmospheric CO2 should warm the planet.
  • Geologic evidence links CO2 and temperature in the past.
  • The warming is unprecedented in the most recent centuries (dwarfs natural variability).
  • Climate models show that rising CO2 is necessary to simulate
  • 20th century temperature trends (solar and volcanic minor players).
slide5

Ice core climate and CO2 records

tiny gas bubbles

in the ice trap

ancient air samples

slide6

#2

Atmospheric CO2 and temperature over the past 650 thousand years

CO2 and temperature

are closely linked

on geologic timescales

slide7

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

#3

The “Hockey Stick”

Key Points:

error bars increase as you go back in time

natural variability accounts for <0.5ºC over the last millennium

late 20th century temperature trend is unprecedented

slide9

#4

anthropogenic only

Solar and volcanic only

Intergovernmental

Panel on

Climate Change

(IPCC) 2001

natural & anthropogenic

slide10

The uncertain climate future

Range of scenarios:

Strict international agreements  CO2 at 600ppm by 2100 *390ppm today

Mid-ground  850ppm by 2100 280ppm 1800

Business as usual  1550ppm by 2100

IPCC AR4, 2007

slide11

but we need to know about

regional climate changes, and specifically

about regional precipitation changes

white = models disagree

color = models mostly agree

stippled = models agree

IPCC AR4, 2007

slide12

Research Goal: constrain tropical Pacific response to anthropogenic

global warming

Approach: reconstruct tropical Pacific climate at high-resolution for

the last millennium

El Niño Temperature

WHY?

“El Niño-Southern Oscillation”

(ENSO)

ENSO is a climate pattern in the

tropical Pacific which arises

from coupled interactions between

the atmosphere and ocean

ENSO impacts global climate every

2-7 years (huge impact on rainfall)

Tropical Pacific climate variability

over decades to centuries to

millennia poorly constrained

El Niño Precipitation

Dai and Wigley, 2000

slide13

ENSO std in control run

ENSO std Observed

ENSO std in GHG run

El Niño

La Niña

Tropical Pacific climate and global warming

both

more El Niño’s

Collins et al., 2004

  • We don’t know how the tropical Pacific will respond to global warming, if at all.
  • Studies are contradictory because:
  • climate data are scarce prior to 1950
  • climate models do not simulate ENSO
  • accurately

Timmermann et al., 1999

more La Niña-like

Cane et al., 1997

slide14

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

Palmyra

1997-?

Fanning

2005-?

Christmas

1998-?

slide15

Corals: The geologic record of El Niño

Living Porites corals provide records

for the last 200 years

CORALS from the tropical Pacific

record El Niño’s in the geochemistry

of their skeletons

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

slide17

Generating climate reconstructions from the Palmyra corals:

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

Aerial view of Palmyra

slide18

Medieval Warm Period (MWP)

Greenland green

Little Ice Age (LIA)

canals frozen in Europe

The Palmyra Island Coral Collection

Modern

slide20

Overlapping fossil corals: ancient El Niño events

Good reproducibility between coral geochemical records

increases confidence in coral climate reconstructions.

slide21

A millennium-long reconstruction of tropical Pacific temperature

Key climate observations:

1) late 20th century warming is unprecedented in the last millennium

2) no cooling during the Northern Hemisphere’s “Little Ice Age”

3) significant cooling implied during the NH’s “Medieval Warm Period”

slide22

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
slide23

The uncertain sea level future

  • 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 estimate
  • using no acceleration
slide26

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)

slide28

uneven warming

will shift rainfall

patterns

Projected temperature change: global view

Take-homes:

-poles warm more

-land warms more

-ocean warming

patchy and complex

slide29

Regional models use global model output,

run at high-resolution (5km) grid

Length of heat waves increase

(# days/event)

Peak temperatures increase

Diffenbaugh et al, 2005

US

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

slide30

Projected precipitation change: global view

white = models disagree

color = models mostly agree

stippled = models agree

Projecting precipitation is VERY uncertain business,

yet extremely critical to human impacts.

slide31

Projected precipitation change: regional view

change in yearly

average precipitation

# dry days

# heavy rain days

mm/day

days/yr

days/yr

Diffenbaugh et al, 2005

slide32

IPCC says increase

in hurricane intensity

“likely” (66%)

slide33

CERTAIN

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.

UNCERTAIN

slide34

What is a country to do?

  • There are only three (prudent) options:
  • 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?

slide36

Some clear lessons:

  • 1) efficiency makes $$
  • gains from cellulosic
    • biofuels likely (not
    • corn ethanol!)
  • 3) taking CO2 out of the sky
  • is more costly than
  • not putting it in the
  • atmosphere to begin with
slide37

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/economics

of global warming.

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