G. Comer Foundation

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USNC INQUA AMQUA NAGT/DLESE On the Cutting Edge
Teaching Climate Change with Ice Core Data,
celebrating IPY, June 2, 2008, State College, PA
G. Comer Foundation
Please note I work for Pennsylvania State
University, And help UN IPCC, NRC, etc., But I
am not representing them, Just me.
Ice Cores, Climate Change and Polar See-saws
What Nature Does And Doesn't Do To Our Climate
Richard B. Alley Penn State
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Ice core on light table, central Greenland.
Depths of 1411.8 m and 1411.9 m (slightly less
than a mile) are noted. The mass-loss summer
layers have made bigger-bubbled layers that
appear dark here (blue bars), and compaction and
ice flow have moved the layers closer together.
These are about 8400 years old.
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Ice cores give wonderful climate records

• Age from counting annual layers, etc. (checked
  many ways!)
• Snow accumulation from layer thickness with flow
  correction, other ways
• Temperature at site in several ways
• Wind-blown dust, sea-salt, etc. from elsewhere
• Trapped bubbles of old air with swamp-gas
  methane, etc.
• All on common time scale.

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Dating (ice-core age)

• Count annual layers
• Count more than once (I re-did half a mile of
  Greenland ice)
• In more than one way (visible, electrical,
  chemical, isotopic indicators)
• By more than one person (blind intercomparisons--n
  o cheating!)
• Check vs. independent ages (chemically
  fingerprinted fallout of historically dated
  volcanoes radiometric, tree-ring varve ages of
  abrupt climate changes)
• Other correlations (esp. all ice cores share same
  gas record), flow models, etc.

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Snow accumulation rate

• Annual-layer thickness, after flow correction
• Ice sheet spreads and thins, melting at edges or
  making icebergs
• Snowfall more-or-less fills space from thinning
• Layers moving halfway to bed thinned by 1/2
• Mathematically un-thin (also correct for air in
  bubbles) to get original thickness
• Others (change of snow to ice controlled by
  temperature and accumulation rate, and recorded
  in gas isotopes and bubble number density, so
  measure these and estimate past temperature to
  learn past accumulation).

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Others

• If it blows through the air, it lands on the ice
• Dust, sea salt, pollen, micrometeorites,
  cosmic-ray-produced nuclides, volcanic ash,
  pollutant
• Once you know snow accumulation rate, you can
  tell whether an ice layer is dirtier because it
  received more dirt, or less snow to dilute dirt
• Thus, the ice yields histories of cosmic-ray
  intensity (modulated by sun and magnetic field),
  space-dust infall, dust production and transport,
  pollution, volcanic eruptions, etc
• Can fingerprint things--e.g., central Greenland
  dust from Asia, Antarctic dust from Patagonia.

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Temperature--Isotopic Ratios

• 1 molecule in 500 in ocean has 1 or 2 extra
  protons in one or more atoms 2H (also called
  deuterium) instead of 1H, or 17O or 18O instead
  of 16O
• The heavier molecules evaporate with greater
  difficulty, condense more easily
• As air mass moves over ice sheet, heavy
  preferentially condenses to fall as snow
• Colder--gtmore water removed from air--gt more
  heavy removed--gtless heavy left--gt isotopically
  lighter snow.

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Temperature--Borehole Temperature

• In Greenland, ice 1 mile down colder than
  surface and colder than bed, because not done
  warming from ice age (works in Antarctica, and in
  ground, too)
• Consider cooking a turkey vs. hot-dog vs. your
  skin if you touch the stove burner--twice as big
  takes four times as long
• Temperature of ice today remembers how cold the
  ice-age was
• Fuzzy memory--can learn temperature last night,
  last winter, last century, last millennium, and
  last ice age.

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Temperature--Gas isotopes

• After abrupt warming, takes 100 years to warm
  ice 70 m down where bubbles are trapped from the
  air spaces in the snow
• Takes 5 years for gas to diffuse through spaces
  to bubble-trapping depth
• If not wind-mixed, heavy gases go to cold end
  (well-known physics even tried for isolating
  uranium isotopes for bombs)
• Causes slight anomaly in trapped gases
• Anomaly size shows abrupt-warming size.

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Temperature--More

• Count years between ice-phase and gas-phase
  record of abrupt warming
• Measure gas-isotopic anomaly caused by
  gravitational separation to bubble-trapping depth
  in non-wind-mixed firnold snow (Todd Sowers
  discovered)
• Measure bubble number-density, controlled by time
  and temperature to trapping depth
• All three depend on snowfall and temperature over
  time to bury snow to trapping depth
• So allow check on temperature, snowfall history
  estimates.

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Gases

• Snow turning to ice traps old air
• Only reliable samples of old air known
• Reliable? Yes.
• Good agreement with instrumental record
• Good agreement between records from different
  cores from different places with different
  snowfall, temperature and impurities
• Records of abrupt changes offset by firn depth,
  not where chemistry changed
• Breaking points fairly well known (too warm or
  too dirty and get poor agreement among cores or
  with instrumental record, and gas changes where
  chemistry changes).

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So, ice cores show

• Sun matters to climate, but
• Total output changes little
• Redistribution by orbits slow
• Volcanoes matter to climate, but mostly
  noisemakers rather than organized
• Magnetic field, cosmic rays dont matter to
  climate (at least not much)
• Space dust doesnt change much, so doesnt matter
  to climate changes
• CO2 matters to climate
• Ocean circulation, sea ice matter to climate.

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Year
Temperature
1700
1800
1900
Sunspots
We can see solar effect on climate--real but
small (and sun hasnt done anything while
temperatures rose last decades). Greenland
temperatures do correlate significantly with
sunspot numbers, but most Greenland temperature
changes are not explained by sunspots. (GISP2
ice-core ?18O, 5-20 yr bandpass, data from
1700-1930, shifted for optimal correlation
correlation is highly significant, but accounts
for only 13 of the power in the passband. Other
solar frequencies are also present, but again
with small power. Stuiver et al., 1995)
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Volcano erupts
Acid falls on Greenland
Cooling from volcanoes
Big volcanoes cool (1-2oC for 2-3 years). But,
big volcanoes cant get organized, so they
havent wont control climate. (Stack of
GISP2, Greenland ?18O records from 7 VEI 6-7
eruptions Stuiver et al. 1995.)
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Today
Climate didnt change
Warmer
Climate didnt change
When more cosmic rays reached Earth
Cosmic rays, magnetic field dont matter much to
climate.
From Muschler et al., 2005, QSR. ?18O (proxy for
temperature) from GRIP core (top), the
concentration of 10Be (middle), and the flux of
10Be (bottom). The Laschamp event of near-zero
magnetic field (red arrow) allowed increased
cosmic-ray flux producing more 10Be, but with no
apparent effect on climate.
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Changes in space dust have been small, and
havent affected climate much. Helium-3 is mostly
from space dust. If space dust changed a lot,
that might affect climate some. But there has
been little change in space dust over last 30,000
years (ice-core data shown here) and beyond
(other data not shown). (Very rarely, a big
meteorite does matter, such as the one that
killed the dinosaurs 65 million years ago.)
Winckler Fischer, 2006, Science
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Petit et al., 1999
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So, ice age cycle

• Orbits move sun around on planet (big changes
  locally, tiny globally)
• Global climate mostly has followed northern sun
• Sun affects snow, ice, dust, sea level, ocean
  circulation, plants which affect temperature
• These other changes affect CO2, which affects
  temperature
• If CO2 warms, temperature history makes sense
• If CO2 doesnt warm, size of temperature changes
  is unexplained.

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An ice-age analogy Suppose

• I overspend my credit card and go into debt
• Interest charges increase my debt
• The interest charges clearly lag the debt
• But, an accountant must consider interest as well
  as overspending to explain my debt
• For the ice ages
• Orbits force temperature as overspending forces
  debt
• Temperature, others force CO2 as debt forces
  interest
• CO2 amplifies temperature as interest amplifies
  debt
• Lots of apparently rational people say CO2 lags
  warming, so CO2 cannot contribute to warming.
  They also must believe that interest charges
  cannot contribute to debt.

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Without change in human behavior, our students
will see the CO2 leave the page, and we may see
this, too.
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Independent dating Fairly clearly same record.
Cold Greenland dry China
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Ice-dammed floods
Ice-sheet surges
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Image courtesy W. Curry, WHOI
DRY
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North Atlantic abrupt changes

• Switchfreeze vs. sink in winter
• Differencegt20oC in winter locally
• Big deal is probably rain in the monsoons--fresh
  and winter-frozen North Atlantic has gone with
  dry monsoon (few billion people)
• gt90 confidence that Greenland will melt slowly
  enough to avoid this
• But gt90 is not 100
• Like a lot of things in the climate-change
  game--even if unlikely, there is a possibility of
  really bad things.

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So where are we???

• Ice cores outstanding--an immense amount learned,
  more to come, highly reliable
• This deeper-time perspective supports the
  shallow-time perspective of climate science
• Changes in sun matter, but are slow (orbital) or
  small (faster)
• Volcanoes unorganized noisemakers
• Cosmic rays, magnetic field, space dust, others
  you might think of really dont matter much
• Greenhouse gases (esp. CO2) matter a lot
• There may be surprises in the greenhouse

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