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Greenhouse gases and climate information from polar ice cores
Dr. Ed Brook, Oregon State University
US Ice Drilling Program
Three Messages
 Humans have radically altered the amount
of atmospheric greenhouse gases.
 Greenhouse gases and climate are linked
tightly in the record from ice cores.
 We should expect warming, and sea level
change, as greenhouse gas levels rise in the
Greenhouse Effect
 Greenhouse gases are like
a dam on a river. They
increase the amount of
heat in the atmosphere.
 Major ones are water
vapor, carbon dioxide
(CO2), methane (CH4),
and nitrous oxide (N2O).
 Without them earth would
be -18˚C (0˚F)
 The greenhouse effect is
well understood. It was
articulated in the early
1800’s by Joseph Fourier,
but influenced by earlier
The Changing Atmosphere
“The Keeling Curve”
 Modern measurement
network is sophisticated
and accurate
 Systematic, direct
measurements of
greenhouse gases since
the 1950’s at best.
 What happened before
Polar Ice Cores
WAIS Divide
Gases in Ice Cores
Gas Extraction and Analysis
Dry Extraction
Crushing under vacuum
Analysis by gas
chromatography, laser
spectroscopy, mass
Wet Extraction
Melting under vacuum
Analysis by gas
chromatography, laser
spectroscopy, mass
Other Climate Information from
Ice Cores
 Snowfall rate from layer
Temperature from stable
isotopes (18O/16O, or 2H/1H) of
Dust and aerosol content of
atmosphere from chemical
Ice sheet elevation from total
air content
Pre-ice sheet history from
basal material
Drilling at WAIS Divide
The Human Impact: CO2
Industrial Revolution
40% Increase since 1700s
The Human Impact: Methane
240% Increase since 1700s
The Long View
Dome C Ice Core - Antarctica
Preindustrial Carbon Dioxide
Preindustrial Methane
Antarctic Temperature
*Greenhouse Gases and Climate Change Together in Natural Cycles
*No Precedent for Modern Greenhouse Gas Levels in last 800,0000 years
A Good Analogy
What Do These Data Tell us
About Climate Change?
 The modern atmosphere is very different than
the previous 800,000 years.
 Can’t explain the warm periods of the past
without greenhouse gases. Gases always higher
during warm periods.
 The climate system works the way we think it
does. In detail there are puzzles we spend lots of
time on, but we understand that greenhouse
gases cause warming. That warming is
happening now, and will continue.
What about the Future?
 Need models. They are
good, but not perfect.
 Models predict the last
century pretty well.
 Models respond to
greenhouse gases in ways
that are similar to what we
see in the past.
 Models don’t predict small-
scale regional climate that
well yet, but things are
getting better.
What about the Future?
 To predict the future we need to know how greenhouse
gases will change.
 How much will they increase?. A lot in the short run, but
the range of “a lot” matters for prediction of climate.
 Warming by 2100 is about 2-4˚C (4-7 ˚F) by most
 Ice age to present warming was about 5˚C (9˚F).
 Sea level is rising, and will continue to rise. The future
amount is uncertain because how ice sheets behave is
not known well. More than a meter by 2100 is possible.
WAIS Divide Camp, Antarctica
Global Temperatures and Sea Level
 ~1˚C of warming
since 1850. Likely that
~ 50% due to human
 ~ 20 cm sea level
change in the same
time period
 Decreases in snow
cover and sea ice,
and increases in