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Meltdown – Evidence of Climate
Change from Polar Science
Eric Wolff
([email protected])
Why are the polar regions
important for climate?
Heat engine
Why are the polar regions
important for climate?
Heat engine
The colour of the Earth
Polar amplification
Temperature (ºC) 2000-2005 relative to 1951-1980 (Hansen et al., 2006)
Ocean heat transport
Sea level
Past climate
from ice cores
Part I: Learning from the past – ice cores
Part II: Climate change in the polar regions
If we use the past to understand the processes, then we
can hope to have correct models to predict the future
The ice core record
One of many sedimentary records
Very good at recording the atmosphere
800,000 years (Antarctic) and 123,000 years (Greenland)
Accumulation zone
Flow lines
Ablation
zone
Bedrock
Main drawback: geographical restriction
Requirements: Permanent ice cover, no significant
melting, positive snow accumulation
⇒Polar regions, high altitude mountain glaciers
Signals in ice cores
• Temperature and amount of snowfall
imprinted in the snow itself
• Many chemicals deposited with the snow,
recording e.g. volcanic eruptions, sea salt,
atmospheric dust,…
• Oxygen, nitrogen, CO2,….(all the stable
molecules in the air) trapped in bubbles
3. As the snow gets deeper,
pressure turns loose snow
into solid ice with trapped air
bubbles. The bubbles contain
a sample of stable gases from
the atmosphere: e.g CO2
The basic argument of
greenhouse warming
• The concentration of major greenhouse
gases has increased significantly due to
human activities
• Physics tells us that increasing the
concentrations of greenhouse gases traps
heat and causes climate on average to warm
Recent past – CO2
375
CO2 / ppmv
350
Mauna Loa atmospheric
Law Dome (Etheridge et al., 1996)
Siple (Friedli et al., 1986)
EPICA DML (Siegenthaler et al., 2005)
S. Pole (Siegenthaler et al., 2005)
325
300
275
250
1000
1200
1400
1600
Age (Year AD)
1800
2000
Recent changes - methane
CH4 / ppbv
1600
Cape Grim air
Law Dome ice
Etheridge et al 1998, JGR 103, 15979.
1200
800
1000
1200
1400
1600
Age / years AD
1800
2000
Time’s arrow!
Discovery of rapid (in a human lifetime)
climate shifts from a Greenland ice core
-30
North GRIP Project Members 2004
North GRIP Project Members 2004
-35
-35
18
δδ18O
‰
O // ‰
WARM
-40
-40
~10ºC
COLD
-45-45
0
0
30
60
90
10
20
30
Age
/
kyr
BP
Age / thousands of years before present
120
40
Footprint of these events
throughout northern hemisphere
Clues to the mechanism
Antarctica vs the
north
Blunier and Brook 2001 (Science)
Significance of D-O events
• Rapid change has occurred in the past, but
as far as we know only when there are large
ice sheets
• But models for the future do suggest
changes in thermohaline circulation
• Need to better understand past changes and
test models against them
European Project for Ice Coring
in Antarctica (EPICA)
60
°S
70
Dronning
Ma ud La nd
°S
Be rkne r
Isla nd
Dome F
80
°S
Byrd
Vostok
La w Dome
Dome C
Siple Dome
Ta ylor
Dome
0km
1,000km
2,000km
Dome C
75ºS
3233 m asl
~25 kg m-2 yr-1
Mean T:-54.5ºC
DML
75ºS
2892 m asl
~64 kg m-2 yr-1
Mean T:-44.6ºC
Dome C
• Depth reached 3270
m (bedrock 3275 m)
• Best estimate of
useable age ~800 kyr
• Final 70 m drilled in
December 2004
After drilling, the core must be stored and transported
frozen back to analytical laboratories
Estimated Antarctic temperature
Estimated Dome C
temperature difference / °C
5
0
-5
-10
0
200
400
600
Age / thousands of years before present
EPICA Community Members, Nature, 429, 623-628, 2004;
Jouzel et al., Science, 2007
800
Estimated Antarctic temperature
Estimated Dome C
temperature difference / °C
5
0
-5
-10
0
200
400
Age / EDC3 ka bp (1950)
600
EPICA Community Members, Nature, 429, 623-628, 2004;
Jouzel et al., Science, 2007
800
What does CO2 do in a changing climate?
CO2 / ppmv
300
Siegenthaler et al 2005
275
250
225
Estimated Dome C
temperature difference / °C
200
5
175
0
-5
-10
0
200
400
Age / EDC3 ka bp (1950)
600
800
But we are out of the range of the last 800 kyr
400
CO2 / ppmv
350
300
250
200
200
600
Age / ka BP
Siegenthaler et al., Science 2005 (EPICA gas consortium)
For CH4 (methane) also
δD ice / ‰
EPICA
EPICADome
DomeCCdata
data
WARM
WARM
-390
-390
COLD
COLD
-420
-420
-450
-450
Vostok + Dome C data
CH
CH44 // ppbv
ppbv
700
1500
600
1000
500
Vostok + Dome C data
400
500
300
00
200
200
400
400
Age
Age // kyr
kyr BP
BP
600
600
Spahni et al., Science 2005, EPICA gas consortium
800
800
Dome C
detailed CO2
Monnin et al (2001)
Science 291, 112-114
Phasing is
consistent with CO2
as an amplifier
(NB latest papers
suggest we should
bring CO2 forward
a few hundred
years)
Summary – ice core records
• A fantastic archive of our past
• Have provided our only clear record of recent
greenhouse gas increases
• Over longer periods shown strong link between
climate and greenhouse gases
• Revealed existence of past rapid climate change
• Shows us how Earth works: needed for future
prediction
Part I: Learning from the past – ice cores
Part II: Climate change in the polar regions
Courtesy of NASA/GISS
The cryosphere
The cryosphere is the portion of the Earth's surface where
water is in a solid form, usually snow or ice. This includes sea
ice, freshwater ice, snow, glaciers, and frozen ground (or
permafrost).
NISE product, courtesy NSIDC
The cryosphere today
Arctic sea ice
Area /
106 km2
14 (winter)
Antarctic sea ice
17.1 (winter)
NH snow cover
44 (winter)
Volume / Sea level
106 km3 equiv / m
Glaciers/ice caps 0.5
0.1
0.30
Greenland ice
1.7
2.9
7.3
Antarctic ice
12.3
24.7
56.6
IPCC 2007
Recent trends – Arctic sea ice
IPCC AR4, 2007
Reduction of 7% per decade
Reductions in thickness also reported (but
somewhat controversial)
Sea ice
NASA
1979-1981
2003-2005
Antarctic sea ice
Bellingshausen/Amundsen Sea
Ross Sea
Regional variations;
little net change
Southern hemisphere
Predicting future sea ice
Ice sheets and sea level
• Greenland ice contains 7 m of sea level
• Antarctic ice contains 60 m of sea level
• IPCC (4th AR) projects 18-59 cm of sea level rise
by 2100
• But ignores contributions from ice flow
instabilities (no basis for quantifying)
• And this figure takes no account of later sea level
rise that we will soon commit to
Ice sheets
• Within uncertainties, the Antarctic ice sheet has
been close to being in balance in recent decades
• Most obvious change in Antarctica has been the
loss of Antarctic Peninsula ice shelves
• West Antarctic glaciers showing retreat and ice
loss than is not yet explained
• Some parts of inland Greenland may have
thickened in recent years; some coastal regions
show thinning
East Antarctica –mainly cold and stable to
significant warming
From passive
microwave
measurements
Source: O. Torinesi, M. Fily,
C. Genthon, J. Clim. 16, 1047
(2003).
0
50
Days per year
100
Antarctic Peninsula: Ice shelf loss in
response to regional warming
West Antarctic thinning
Ice thickness
changes
1992-2003
Source:
Source: Wingham
Wingham et
et al.,
al., 2006
2006
Greenland:
coastal retreat
1992-2003
Greenland
At warming somewhere between 1.9
and 4.6ºC, net ablation exceeds net
accumulation and eventual loss of ice
sheet appears inevitable
Greenland: long-term
A 3º warming might imply a commitment to up to 6 m sea level rise
Longer-term prognosis
• Continued warming beyond next century likely to
remove most small glaciers and most Arctic sea
ice
• East Antarctica is so cold that significant surface
melting cannot occur; should be stable unless ice
dynamics surprises
• West Antarctica – prognosis somewhat unclear
• Greenland – prognosis poor
Summary
• The polar regions are important for many aspects
of climate change
• Ice cores tell us that greenhouse gas
concentrations really have risen, that very fast
climate change is possible, and show us how the
Earth’s climate system works
• The polar cryosphere is shrinking, and there are
many aspects of that which we don’t yet
understand
Of course it might be worse than
I think!
Thank you