Climate Change: New Antarctic Ice Core Data


Richard Moore

Original source URL:
[graphs in original]

Climate Change: New Antarctic Ice Core Data
The information in this web page was researched on Earth Day, 2000.
This page was last updated on May 30, 2000.

In June of 1999 the latest ice core data from the Vostok site in Antarctica were
published by Petit et al in the British journal Nature.  These new data extended
the historical record of temperature variations and atmospheric concentrations 
of CO2, methane and other greenhouse trace gases (GTG) back to 420,000 years 
before present (BP).  The ice cores were drilled to over 3,600 meters.  This is 
just over 2.2 miles deep.  These new data double the length of the historical 

The main significance of the new data lies in the high correlation between GTG 
concentrations and temperature variations over 420,000 years and through four 
glacial cycles.  However, because of the difficulty in precisely dating the air 
and water (ice) samples, it is still unknown whether GTG concentration increases
precede and cause temperature increases, or vice versa--or whether they increase
synchronously.  It's also unknown how much of the historical temperature changes
have been due to GTGs, and how much has been due to orbital forcing, ie, 
increases in solar radiation, or perhaps long-term shifts in ocean circulation.

Whether the ultimate cause of temperature increase is excess CO2, or a different
orbit, or some other factor probably doesn't matter much.  It could have been 
one or the other, or different combinations of factors at different times in the
past.  The effect is still the same.  Nevertheless, the scientific consensus is 
that GTGs account for at least half of temperature increases, and that they 
strongly amplify the effects of small increases in solar radiation due to 
orbital forcing.

The graph below includes data from the Nature paper, plus data from other 
studies referenced below.  Notice how CO2 concentration rises vertically at the 
end of the time series.  The increase appears vertical because of the large time
scale, but it actually occurs over the past 150 years, which corresponds to the 
age of fossil fuels (the modern industrial age).   Notice too that there hasn't 
been a corresponding increase in temperature during this time period.  This is 
probably due to the ability of the oceans to function as a heat sink, and 
thereby delay the increase in atmospheric temperatures.  However, there are 
recent indications that the oceans are now warming, which will reduce their 
ability to act as a heat sink.

Note on graph presentation: The heavier temperature lines 160,000 BP to present 
reflect more data points for this time period, not necessarily greater 
temperature variability.

Other interesting patterns in the data include the extreme increases and 
decreases in temperature preceding and following the interglacial phases (the 
five high temperature phases in the graph).  Some possible reasons for this 
pattern are explained in the research papers referenced below.  In particular, 
positive feedback mechanisms are instrumental in rapid temperature increases.  
In any case, the current interglacial period is the longest on record.  The 
current interglacial is also unique in that maximum temperatures have not 
increased above +2C relative to the mid-20th century benchmark (0C) for very 
long.  It would appear that the +2C threshhold must be exceeded for some period 
of time to initiate a new glacial phase.  Or perhaps the threshold is +1C, but 
for a longer period of time.  The present mean temperature is about +.8C.  
Recent peak temperatures have been in the +1.4C to +1.6C range.  See the Data 4 
graph on the next page.

Paleoclimatologists theorize that interglacial periods come to an end when polar
ice caps melt rapidly (due to high atmospheric temperatures) and increase the 
amount of fresh water in the sub-polar oceans, thereby altering the thermohaline
circulation patterns which govern global climate.  The thermohaline "conveyor 
belts" essentially shut down and stop moving warm water and air away from the 
equator toward the poles.  The net result is colder water and air temperatures.
These colder temperatures deepen and continue despite high GTG concentrations 
left over from the previous interglacial phases.

Given all the new ice core data, what changes can we anticipate for our climate?
If CO2 has increased over the past 150 years as much as it normally increases 
over thousands of years leading up to an interglacial phase (about 80 ppmv), 
then we could expect as much as a corresponding 10-12C increase in temperature.
But if half the historical temperature increases have been due to orbital 
forcing and other factors, then we should expect an increase of "only" about 
5-6C, or 9-11F.

Most computer models don't predict either of these magnitudes of temperature 
change for the new century.   They typically cite evidence indicating that 
overall global temperatures have not changed as much as polar temperatures, 
where the ice cores were taken, and that increases of only 2-3C should be 
anticipated.  Unfortunately, new evidence from high-elevation tropical ice cores
indicates that this is not really the case.  The latest data show that the 
amplitude of sub-polar temperature changes has been in the range of 8-12C, which
is not all that different from the 10-12C found at the poles.

Thus we seem to be headed for some very large climate changes.  Temperatures 
could increase rapidly, and then decrease just as rapidly--as they have 
repeatedly over the past 420,000 years.  Another possibility is that there will 
be so much GTGs in the atmosphere that they will actually override historical 
patterns of thermohaline circulation and climate change.  It's noteworthy in 
this context that the current atmospheric methane level is about 230% of its 
pre-industrial maximum (contrasted with CO2 being about 130% of its 
pre-industrial maximum).  For closer looks at the ice core data for the 18,000 
year, 200 year, and 50 year time frames, go to the next page.

Graph Data

1) Historical carbon dioxide record from the Vostok ice core: Graphics & Digital

Period of Record: 414,085-2,342 years BP

J.M. Barnola, D. Raynaud, C. Lorius, Laboratoire de Glaciologie et de 
Géophysique de l'Environnement, CNRS, BP96, 38402 Saint Martin d'Heres Cedex, 

N.I. Barkov, Arctic and Antarctic Research Institute, Beringa Street 38, 199397,
St. Petersburg, Russia

2) Historical Isotopic Temperature Record from the Vostok Ice Core: Graphics & 
Digital Data

Period of Record: 420,000 years BP-present

J.R. Petit, D. Raynaud, and C. Lorius: Laboratoire de Glaciogie et Géophysique 
de l'Environnement, CNRS, Saint Martin d'Hères Cedex, France

J. Jouzel and G. Delaygue: Laboratoire des Sciences du Climat et de 
l'Environnement (LSCE), CEA/CNRS, L'Orme des Merisiers, CEA Saclay, 91191, 
Gif-sur-Yvette Cedex, France

N.I. Barkov: Arctic and Antarctic Research Institute, Beringa Street 38, 199397 
St. Petersburg, Russia

V.M. Kotlyakov: Institute of Geography, Staromonetny, per 29, Moscow 109017, 

3) Holocene Carbon-cycle Dynamics Based on CO2 Trapped in Ice at Taylor Dome, 
Antarctica. 1999. A. Indermühle, T. F. Stocker, F. Joos, H. Fischer, H. J. 
Smith, M. Wahlen, B. Deck, D. Mastroianni, J. Tschumi, T. Blunier, R. Meyer & B.
Stauffer. Nature 398: 121-125.

4) Historical CO2 records from the Law Dome DE08, DE08-2, and DSS ice cores. 
1998. Etheridge DM, Steele LP, Langenfelds RL, Francey RJ, Barnola JM and Morgan
VI. In Trends, "A compendium of data on global change," Carbon Dioxide 
Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN.

5) Monte Carlo inverse modelling of the Law Dome (Antarctica) temperature 
profile. 1999. D Dahl-Jensen, VI Morgan, A Elcheikh. Annals of Glaciology 
29:145-150. [Data interpolated from graph in Figure 4b]

6) Atmospheric CO2 concentrations (ppmv) derived in situ air samples collected 
at Mauna Loa Observatory, Hawaii. 1999. Keeling CD, Whorf TP. Carbon Dioxide 
Information Analysis Center.

7) Annual and Seasonal Temperature Deviations in the Troposphere and Low 
Stratosphere, as derived from radiosonde records, 1958-1998. Temperature 
deviations (in relation to a 1958-1977 average) expressed in degrees Celsius for
Win (December-February), Spr (March-May), Sum (June-August), and Fall 
(September-November). South Polar (60 degrees S - 90 degrees S)August 1999. 
Source: J. K. Angell. Air Resources Laboratory, National Oceanic and Atmospheric
Reference Papers

Climate and atmospheric history of the past 420,000 years from the Vostok ice 
core, Antarctica. 1999. Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola 
J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G., Delmotte M. 
Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., 
Saltzman E., Stievenard M. Nature 399: 429-436.

The ice record of greenhouse gases : a view in the context of future changes. 
2000. Raynaud, D., J. M. Barnola, J. Chappellaz, T. Blunier, A. Indermuhle and 
B. Stauffer. Quaternary Science Reviews 19: 9-17.

Ice core evidence for climate change in the Tropics: implications for our 
future. 2000. Lonnie G. Thompson. Quaternary Science Reviews 19: 19-35.

Background Information
Ice Core Dating
By Matt Brinkman
Sudden climate transitions during the Quaternary
By Jonathan Adams, Mark Maslin & Ellen Thomas
Deciphering Mysteries of Past Climate from Antarctic Ice Cores
American Geophysical Union.

Remembrance of Things Past: Greenhouse Lessons from the Geologic Record

By Thomas J. Crowley
Learning from Polar Ice Core Research
American Chemical Society
EDF Global Warming Projections for the New Millennium
The Vostok ice core data
By Hugh

Ice core records of atmospheric CO2 around the last three glacial terminations. 
1999. Fischer, H., Wahlen, M., Smith, J., Mastroianni, D. and Deck B. Science 
283: 1712-1714.

The NOAA Paleoclimatology Program has dedicated this section to studies and 
data, as well as science research articles that focus on issues important to 
climate and paleoclimatology.

NOAA Paleoclimatology Program, International Ice Core Data Cooperative.

Vostok Ice Core Data
World Data Center Data Access & Data Submission

New Ice Core data include CO2 from Vostok , and Taylor Dome CO2 for 11-0 KYrBP, 
27-11 KYrBP and 60-20 KYrBP , plus GRIP N2O.  WDC Paleo Data is also mirrored at
several sites around the world.

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