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 14 Sep 2007 NOAA and NSIDC data 05 Sep 1980

Climate: the polar regions are • Iconic: undergoing changes visible at planetary scale • A centre of action: due to polar amplification of 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 Desirable • Monotonic chronological • Good temporal resolution sequence • Length of record • Some feature of it that changes • Geographical spread of in response to changes in the available records parameter you want (for • Cheap and simple collection example, temperature) and analysis • Good signal to noise (temperature is the dominant factor controlling variability) • Robust calibration/transfer function

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 • Dating becomes much • Annual resolution at some poorer in sites with low sites snow accumulation rate • About 800 ka (Antarctic) • Ice cores are and 120 ka (Greenland) geographically limited and available deep cores are expensive • Atmospheric signals to obtain • Many variables on same core (1 ka = 1000 years)

Where can we collect ice cores? Permanent ice cover, no significant melting, positive snow accumulation i.e. Polar regions, high altitude mountain glaciers

The ice core record One of many sedimentary records Very good at recording the atmosphere 800,000 years (Antarctic) and 123,000 years (Greenland) Flow lines Accumulation zone Ablation zone Bedrock

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

Signals in ice cores The snow contains information about the atmosphere in three forms: 1. The isotopic content of the water molecules themselves ( 18 O/ 16 O and D/H) is determined mainly by the temperature at the time of snowfall

2. Soluble and insoluble impurities are trapped at the surface by falling snow, dry deposition and gaseous uptake onto the surface 1815 1883

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 CO 2

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

CO 2 has increased 400 Mauna Loa atmospheric Law Dome (Etheridge et al., 1996) Siple (Friedli et al., 1986) EPICA DML (Siegenthaler et al., 2005) 360 S. Pole (Siegenthaler et al., 2005) CO 2 / ppmv 320 280 1000 1200 1400 1600 1800 2000 Age / year AD

And so has methane (CH 4 ) 1800 MacFarling Meure et al. (2006); Etheridge et al. (1998) Ice and firn air Line is Cape Grim air Etheridge et al 1998, JGR 103, 15979. 1200 CH 4 / ppbv 600 0 1000 1200 1400 1600 1800 2000 Age / years AD

European Project for Ice Coring in Antarctica (EPICA) 60 S ° Dronning Dome C Maud L and 70 S ° 75ºS B erkner Dome F 3233 m asl Island 80 S ° ~25 kg m -2 yr -1 Mean T:-54.5ºC DML B yrd V ostok 75ºS S iple Dome L aw Dome Dome C 2892 m asl T aylor ~64 kg m -2 yr -1 Dome 2,000km 1,000km 0km Mean T:-44.6ºC

Dome C • Depth reached 3270 m (bedrock 3275 m) • Best estimate of useable age ~800 ka

Estimated Antarctic temperature 5 Temperature relative to last thousand years / ° C 0 -5 -10 800 600 400 200 0 Age / thousands of years before present 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 Estimated Antarctic temperature • Every warm period is different! 5 Temperature relative to last thousand years / ° C 0 -5 -10 800 600 400 200 0 Age / thousands of years before present EPICA Community Members, Nature , 429 , 623-628, 2004; Jouzel et al., Science , 317 , 793-796, 2007.

What does CO 2 do in a changing climate? 300 Lüthi et al 2008 CO 2 / ppmv 250 200 Temperature relative to last thousand years / ° C 5 0 -5 -10 800 600 400 200 0 Age / thousands of years before present • CO 2 responsible for 30-50% of the glacial-interglacial warming • probably controlled mainly through processes in the Southern Ocean

But we are out of the range of the last 800 ka 400 • In rate as well as concentration: 350 – Last termination rate was ~20 ppmv/1000 years CO 2 / ppmv 300 – 20 ppmv increase in last 11 years 250 200 Temperature relative to last thousand years / ° C 5 0 -5 -10 800 600 400 200 0 Age / thousands of years before present

280 Dome C 260 detailed CO 2 CO 2 / ppmv 240 Updated from Monnin et al (2001) Science 291, 112-114 220 200 Phasing is consistent with CO 2 as an amplifier Temperature relative to last 1000 yrs / ° C 0 -5 -10 21000 18000 15000 12000 9000 Age / years before present

For CH 4 (methane) also 1800 800 Loulergue et al 2008 1600 1400 CH 4 / ppbv CH 4 / ppbv 1200 600 1000 800 600 400 400 Temperature relative to Temperature relative to last thousand years / ° C last thousand years / ° C 5 5 Jouzel et al 2007 0 0 -5 -5 -10 -10 800 800 600 600 400 400 200 200 0 0 Age / thousands of years before present Age / thousands of years before present

Many other things we can measure – but ice cores are only part of the picture Tenaghi Philippon, Greece 100 LR04 benthic stack pollen / % 2.5 18 O marine / ‰ Arboreal 75 3.0 50 25 3.5 0 18 O marine / ‰ LR04 benthic stack 2.5 4.0 δ 3.0 4.5 3.5 EPICA Dome C 4.0 δ D ice / ‰ δ -390 4.5 EPICA Dome C δ D ice / ‰ -390 -420 -420 -450 -450 800 600 400 200 0 1000 800 600 400 200 0 Age / thousands of years before present Age / thousands of years before present

And Antarctica is only part of the picture EPICA Community Members, Nature , 429 , 623-628, 2004; Jouzel et al, Science , 317, 793-796, 2007 EPICA Dome C -390 δ D ice / ‰ 9 ° C -420 -450 800 600 400 200 0 Age / thousands of years before present

Greenland Rapid Climate Change -375 Dome C -400 δ D / ‰ -425 -450 NorthGRIP -35 18 O / ‰ -40 δ -45 125 100 75 50 25 0 Age / kyr BP

Discovery of rapid (in a human lifetime) climate shifts from a Greenland ice core (Dansgaard-Oeschger events) -30 -30 NorthGRIP Project Members 2004 North GRIP Project Members 2004 WARM -35 -35 18 O / ‰ 18 O / ‰ ~10ºC -40 -40 δ δ COLD -45 -45 40 120 30 90 20 60 10 30 0 0 Age / thousands of years before present Age / thousands of years before present

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 Beware: Antarctica vs the time running north in reverse Blunier and Brook 2001 (Science)

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