Transcript Document

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
Which of the following are scientific statements?
1) 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.
Which of the following are scientific statements?
1) 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.
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 simulate
20th century temperature trends (solar and volcanic minor
players).
Ice core climate and CO2 records
tiny gas bubbles
in the ice trap
ancient air samples
#2
Atmospheric CO2 and temperature over
the past 650 thousand years
CO2 and temperature
are closely linked
on geologic timescales
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
#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
#4
Solar and volcanic only
anthropogenic only
Intergovernmental
Panel on
Climate Change
(IPCC) 2001
natural & anthropogenic
The uncertain climate future
Range of scenarios:
Strict international agreements  CO2 at 600ppm by 2100
Mid-ground  850ppm by 2100
Business as usual  1550ppm by 2100
*390ppm today
280ppm 1800
IPCC AR4, 2007
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
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
El Niño Precipitation
ENSO impacts global climate every
2-7 years (huge impact on rainfall)
Tropical Pacific climate variability
over decades to centuries to
millennia poorly constrained
Dai and Wigley, 2000
Tropical Pacific climate and global warming
ENSO std in control run
ENSO std Observed
ENSO std in GHG run
La Niña El Niño
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
1950
2) climate models do not simulate
ENSO
accurately
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-?
Corals: The geologic record of El Niño
Living Porites corals provide records
for the last 200 years
Fossil Porites corals enable us to
extend the record back many centuries
CORALS from the tropical Pacific
record El Niño’s in the geochemistry
of their skeletons
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
The Palmyra Island Coral Collection
Modern
Medieval Warm Period (MWP)
Greenland green
900
1000
1100
1200
Little Ice Age (LIA)
canals frozen in Europe
1300
1400
1500
Date (A.D.)
1600
1700
1800
1900
2000
Palmyra coral oxygen isotopes vs. tropical Pacific SST
3
-0.6
-0.4
1
-0.2
0
0.0
-1
0.2
-2
-0.3
18O (‰)
2
-0.2
1
-0.1
0
0.0
0.1
-1
0.2
NIÑO3.4 SST
Palmyra coral
R = -0.84
0.3
-2
1900
1920
1940
Year (A.D.)
1960
1980
2000
18O (‰)
SST Anomoly (°C)
SST Anomoly (°C)
R = -0.66
Overlapping fossil corals: ancient El Niño events
Good reproducibility between coral geochemical records
increases 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 millennium
2) 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 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
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 warming
will shift rainfall
patterns
Regional models use global model output,
run at high-resolution (5km) grid
Length of heat waves increase
(# days/event)
Diffenbaugh et al, 2005
Peak temperatures increase
US
http://www.usgcrp.gov/usgcrp/nacc/se-mega-region.htm
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.
Projected precipitation change: regional view
change in yearly
average precipitation
mm/day
# heavy rain days
days/yr
# dry days
days/yr
Diffenbaugh et al, 2005
IPCC says increase
in hurricane intensity
“likely” (66%)
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
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 (not
corn ethanol!)
3)
taking CO2 out of the sky
is more costly than
not putting it in the
atmosphere to begin with
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