Natural and anthropogenic climate change Lessons from ice cores - - PowerPoint PPT Presentation

Natural and anthropogenic climate change Lessons from ice cores

Eric Wolff British Antarctic Survey, Cambridge ewwo@bas.ac.uk

ASE Annual Conference 2011; ESTA/ESEU lecture

Outline

• What is British Antarctic Survey (BAS), who

am I?

• Why the past, why ice cores?
• How do we collect ice cores?
• How do they work?
• 3 examples of what we have learnt
• Future plans

Climate: the polar regions are

• Iconic: undergoing changes visible at

planetary scale

Arctic sea ice decline

05 Sep 1980 14 Sep 2007 NOAA and NSIDC data

Climate: the polar regions are

• Iconic: undergoing changes visible at

planetary scale

• A centre of action: due to polar amplification
• f climate
• At the root of important impacts (especially

sea level change)

• Vital sources of information about how the

climate system works

Palaeoclimate/palaeoatmosphere

Why do we need to understand the past?

• Curiosity – What? When? Why? Where?
• Processes – Observe how the climate/Earth

system responded under conditions different to those of today

• Model validation – does the world behave

the way models suggest (in ways that matter for the future)?

Criteria for sedimentary records

Essential

• Monotonic chronological

sequence

• Some feature of it that changes

in response to changes in the parameter you want (for example, temperature)

• Good signal to noise

(temperature is the dominant factor controlling variability)

• Robust calibration/transfer

function Desirable

• Good temporal resolution
• Length of record
• Geographical spread of

available records

• Cheap and simple collection

and analysis

Palaeo records

• Historical records
• Tree rings
• Lakes - levels and sediments
• Peat
• Marine sediments
• Ice cores
• Other chronological sequences (e.g. corals)

Advantages and disadvantages to each

Ice cores

isotopic content, gases, chemistry, precipitation

• Well-dated
• Annual resolution at some

sites

• About 800 ka (Antarctic)

and 120 ka (Greenland) available

• Atmospheric signals
• Many variables on same

core (1 ka = 1000 years)

• Dating becomes much

poorer in sites with low snow accumulation rate

• Ice cores are

geographically limited and deep cores are expensive to obtain

Permanent ice cover, no significant melting, positive snow accumulation i.e. Polar regions, high altitude mountain glaciers

Where can we collect ice cores?

Bedrock Flow lines Accumulation zone Ablation

The ice core record

One of many sedimentary records Very good at recording the atmosphere 800,000 years (Antarctic) and 123,000 years (Greenland)

zone

Video courtesy of Lucia Simion (not included in this version)

Signals in ice cores

• 1. The isotopic content of the water molecules themselves

(18O/16O and D/H) is determined mainly by the temperature at the time of snowfall

The snow contains information about the atmosphere in three forms:

• 2. Soluble and insoluble impurities are trapped at the

surface by falling snow, dry deposition and gaseous uptake

• nto the surface

1883 1815

• 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

• Physics tells us that increasing the

concentrations of greenhouse gases traps heat and causes climate on average to warm

• The concentration of major greenhouse

gases has increased significantly due to human activities

CO2 has increased

280 320 360 400 1000 1200 1400 1600 1800 2000

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)

Age / year AD CO2 / ppmv

And so has methane (CH4)

Etheridge et al 1998, JGR 103, 15979.

600 1200 1800 1000 1200 1400 1600 1800 2000 MacFarling Meure et al. (2006); Etheridge et al. (1998) Ice and firn air Line is Cape Grim air Age / years AD CH4 / ppbv

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

0km 1,000km 2,000km 80 S ° 70 S ° 60 S °

V

• stok

Dome F T aylor Dome B yrd Dronning Maud L and S iple Dome Dome C L aw Dome B erkner Island

European Project for Ice Coring in Antarctica (EPICA)

Dome C

• Depth reached 3270

m (bedrock 3275 m)

• Best estimate of

useable age ~800 ka

• 10
• 5

5 200 400 600 800 Age / thousands of years before present Temperature relative to last thousand years / °C

Estimated Antarctic temperature

EPICA Community Members, Nature, 429, 623-628, 2004; Jouzel et al., Science, 317, 793-796, 2007.

• 10
• 5

5 200 400 600 800 Age / thousands of years before present Temperature relative to last thousand years / °C

Estimated Antarctic temperature

EPICA Community Members, Nature, 429, 623-628, 2004; Jouzel et al., Science, 317, 793-796, 2007.

• ~100 ka cycles of warm and cold (warm is short)
• Tendency to stronger cycles in later part of period
• Every warm period is different!

• CO2 responsible for 30-50% of the glacial-interglacial warming
• probably controlled mainly through processes in the Southern Ocean
• 10
• 5

5 200 400 600 800 Age / thousands of years before present Temperature relative to last thousand years / °C 200 250 300 CO2 / ppmv

Lüthi et al 2008

What does CO2 do in a changing climate?

But we are out of the range of the last 800 ka

200 250 300 350 400 CO2 / ppmv

• 10
• 5

5 200 400 600 800 Age / thousands of years before present Temperature relative to last thousand years / °C

• In rate as well as concentration:

– Last termination rate was ~20 ppmv/1000 years – 20 ppmv increase in last 11 years

Dome C detailed CO2

Updated from Monnin et al (2001) Science 291, 112-114

Phasing is consistent with CO2 as an amplifier

200 220 240 260 280 CO2 / ppmv

• 10
• 5

9000 12000 15000 18000 21000 Age / years before present Temperature relative to last 1000 yrs / °C

For CH4 (methane) also

400 600 800

Loulergue et al 2008

CH4 / ppbv

• 10
• 5

5 200 400 600 800

Jouzel et al 2007

Age / thousands of years before present Temperature relative to last thousand years / °C

• 10
• 5

5 200 400 600 800 Age / thousands of years before present Temperature relative to last thousand years / °C 400 600 800 1000 1200 1400 1600 1800 CH4 / ppbv

Many other things we can measure – but ice cores are only part of the picture

2.5 3.0 3.5 4.0 4.5 LR04 benthic stack

δ

18O marine / ‰

• 450
• 420
• 390

200 400 600 800 1000 EPICA Dome C Age / thousands of years before present

δD ice / ‰

• 450
• 420
• 390

200 400 600 800 EPICA Dome C Age / thousands of years before present

δD ice / ‰

2.5 3.0 3.5 4.0 4.5 LR04 benthic stack

δ

18O marine / ‰

25 50 75 100 Tenaghi Philippon, Greece Arboreal pollen / %

• 450
• 420
• 390

200 400 600 800 9°C EPICA Dome C Age / thousands of years before present

δD ice / ‰

EPICA Community Members, Nature, 429, 623-628, 2004; Jouzel et al, Science, 317, 793-796, 2007

And Antarctica is only part of the picture

Greenland Rapid Climate Change

• 45
• 40
• 35

25 50 75 100 125 NorthGRIP Age / kyr BP

δ

18O / ‰

• 450
• 425
• 400
• 375

Dome C

δD / ‰

• 45
• 40
• 35
• 30

30 60 90 120 NorthGRIP Project Members 2004 Age / thousands of years before present

δ

18O / ‰

• 45
• 40
• 35
• 30

10 20 30 40 Age / thousands of years before present

δ

18O / ‰

Discovery of rapid (in a human lifetime) climate shifts from a Greenland ice core

(Dansgaard-Oeschger events)

North GRIP Project Members 2004

~10ºC

WARM COLD

Footprint of D-O events throughout northern hemisphere

• Greenland
• Atlantic SSTs
• Santa Barbara Basin
• Cariaco Basin (Venezuela)
• Arabian Sea
• ?Tropical wetlands (methane)
• ?China (dust to Greenland)

Clues to the mechanism

Blunier and Brook 2001 (Science)

Antarctica vs the north

Beware: time running in reverse

Ideas about mechanism

• Freshwater (ice or lake drainage) to North Atlantic

Changes density structure of ocean, reducing sinking Collapsed or reduced meridional overturning circulation (MOC) Cooling and atmospheric circulation changes in NH (northern hemisphere) Some warming in south (Bipolar seesaw)

• Restart of MOC spontaneous or forced by

freshwater in Southern Ocean

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

Future ice core research

International Partnership in Ice Core Science (IPICS)

• Longer records – Dome C

and beyond (1.5 Ma?)

• Older ice in Greenland (full

interglacial)

• Detailed regional pattern for

transition and Holocene around Antarctica and Arctic

• Spatial pattern of climate

change over last 2000 years (global)

0km 1,000km 2,000km 8 S ° 7 S ° 6 S °

V

• stok

Dome F T aylor Dome B yrd Dronning Maud L and S iple Dome Dome C L aw Dome B erkner Island

Context: longer-term cooling

Age / Ma Based on Zachos et al 2001

3 4 5 2000 4000 6000 Age / thousands of years before present

δ

18O / ‰

3 4 5 500 1000 1500 Age / thousands of years before present

δ

18O / ‰

Changing amplitude and period

From marine sediments (Lisiecki and Raymo 2005 [LR04]) 40 ka 100 ka

Summary – ice core records

• A fantastic archive of our past
• Have provided our only clear record of recent

greenhouse gas increases, as well as data on natural forcings

• 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

Thank you