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 record.
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 toorbital 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.
1) Historical carbon dioxide record from the Vostok ice core: Graphics & Digital Data
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, France
N.I. Barkov, Arctic and Antarctic Research Institute, Beringa Street 38, 199397, St. Petersburg, Russiahttp://cdiac.esd.ornl.gov/trends/co2/vostok.htm
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, Russia
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.http://www.ngdc.noaa.gov/paleo/taylor/indermuehle99nat.pdf
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 Administration.
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.
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
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.