Volume 6, Number 26: 25 June 2003
For the past two decades or more, we have heard much about the global warming of the 20th century being caused by the rise in atmospheric carbon dioxide concentration that is generally attributed to anthropogenic CO2 emissions. This story, however, has always been controversial [see Smagorinsky et al. (1982) and Idso (1982) for early pro/con positions on the issue]; and with the retrieval and preliminary analysis of the first long ice core from Vostok, Antarctica -- which provided a 150,000-year history of both surface air temperature and atmospheric CO2 concentration -- the debate became even more intense, as the close associations of the ups and downs of atmospheric CO2 and temperature that were evident during glacial terminations and inceptions in that record, as well as in subsequent records of even greater length, led many climate alarmists to claim that those observations actually proved that anthropogenic CO2 emissions were responsible for 20th-century global warming.
This contention was challenged by Idso (1989), who wrote -- in reference to the very data that were used to support the claim -- that "changes in atmospheric CO2 content never precede changes in air temperature, when going from glacial to interglacial conditions; and when going from interglacial to glacial conditions, the change in CO2 concentration actually lags the change in air temperature (Genthon et al., 1987)." Hence, he concluded that "changes in CO2 concentration cannot be claimed to be the cause of changes in air temperature, for the appropriate sequence of events (temperature change following CO2 change) is not only never present, it is actually violated in [at least] half of the record (Idso, 1988)."
How has our understanding of this issue progressed in the interim? Our website provides several updates.
Petit et al. (1999) reconstructed histories of surface air temperature and atmospheric CO2 concentration from data obtained from a Vostok ice core that covered the prior 420,000 years, determining that during glacial inception "the CO2 decrease lags the temperature decrease by several thousand years" and that "the same sequence of climate forcing operated during each termination." Likewise, working with sections of ice core records from around the times of the last three glacial terminations, Fischer et al. (1999) found that "the time lag of the rise in CO2 concentrations with respect to temperature change is on the order of 400 to 1000 years during all three glacial-interglacial transitions."
On the basis of atmospheric CO2 data obtained from the Antarctic Taylor Dome ice core and temperature data obtained from the Vostok ice core, Indermuhle et al. (2000) studied the relationship between these two parameters over the period 60,000-20,000 years BP (Before Present). One statistical test performed on the data suggested that shifts in the air's CO2 content lagged shifts in air temperature by approximately 900 years, while a second statistical test yielded a mean lag-time of 1200 years. Similarly, in a study of air temperature and CO2 data obtained from Dome Concordia, Antarctica for the period 22,000-9,000 BP -- which time interval includes the most recent glacial-to-interglacial transition -- Monnin et al. (2001) found that the start of the CO2 increase lagged the start of the temperature increase by 800 years. Then, in another study of the 420,000-year Vostok ice-core record, Mudelsee (2001) concluded that variations in atmospheric CO2 concentration lagged variations in air temperature by 1,300 to 5,000 years.
In a somewhat different type of study, Yokoyama et al. (2000) analyzed sediment facies in the tectonically stable Bonaparte Gulf of Australia to determine the timing of the initial melting phase of the last great ice age. In commenting on the results of that study, Clark and Mix (2000) note that the rapid rise in sea level caused by the melting of land-based ice that began approximately 19,000 years ago preceded the post-glacial rise in atmospheric CO2 concentration by about 3,000 years.
So what's the latest on the issue? To our knowledge, the most recent study to broach the subject is that of Caillon et al. (2003), who measured the isotopic composition of argon -- specifically, ð40Ar, which they argue "can be taken as a climate proxy, thus providing constraints about the timing of CO2 and climate change" -- in air bubbles in the Vostok ice core over the period that comprises what is called Glacial Termination III, which occurred about 240,000 years BP. The results of their tedious but meticulous analysis led them to ultimately conclude that "the CO2 increase lagged Antarctic deglacial warming by 800 ± 200 years."
This finding, in the words of Caillon et al., "confirms that CO2 is not the forcing that initially drives the climatic system during a deglaciation." Nevertheless, they and many others continue to hold to the view that the subsequent increase in atmospheric CO2 -- which is believed to be due to warming-induced CO2 outgassing from the world's oceans -- serves to amplify the warming that is caused by whatever prompts the temperature to rise in the first place. This belief, however, is founded on unproven assumptions about the strength of CO2-induced warming and is applied without any regard for biologically-induced negative climate feedbacks that may occur in response to atmospheric CO2 enrichment. Also, there is no way to objectively determine the strength of the proposed amplification from the ice core data.
In consequence of these several observations, the role of CO2 as a primary driver of climate change on earth would appear to be going, going, gone; while the CO2 warming amplification hypothesis rings mighty hollow.
|Sherwood, Keith and Craig Idso|
Caillon, N., Severinghaus, J.P., Jouzel, J., Barnola, J.-M., Kang, J. and Lipenkov, V.Y. 2003. Timing of atmospheric CO2 and Antarctic temperature changes across Termination III. Science 299: 1728-1731.
Clark, P.U. and Mix, A.C. 2000. Ice sheets by volume. Nature 406: 689-690.
Fischer, H., Wahlen, M., Smith, J., Mastroianni, D. and Deck B. 1999. Ice core records of atmospheric CO2 around the last three glacial terminations. Science 283: 1712-1714.
Genthon, C., Barnola, J.M., Raynaud, D., Lorius, C., Jouzel, J., Barkov, N.I., Korotkevich, Y.S. and Kotlyakov, V.M. 1987. Vostok ice core: Climatic response to CO2 and orbital forcing changes over the last climatic cycle. Nature 329: 414-418.
Idso, S.B. 1982. Carbon Dioxide: Friend or Foe? IBR Press, Tempe, AZ.
Idso, S.B. 1988. Carbon dioxide and climate in the Vostok ice core. Atmospheric Environment 22: 2341-2342.
Idso, S.B. 1989. Carbon Dioxide and Global Change: Earth in Transition. IBR Press, Tempe, AZ.
Indermuhle, A., Monnin, E., Stauffer, B. and Stocker, T.F. 2000. Atmospheric CO2 concentration from 60 to 20 kyr BP from the Taylor Dome ice core, Antarctica. Geophysical Research Letters 27: 735-738.
Monnin, E., Indermühle, A., Dällenbach, A., Flückiger, J, Stauffer, B., Stocker, T.F., Raynaud, D. and Barnola, J.-M. 2001. Atmospheric CO2 concentrations over the last glacial termination. Science 291: 112-114.
Mudelsee, M. 2001. The phase relations among atmospheric CO2 content, temperature and global ice volume over the past 420 ka. Quaternary Science Reviews 20: 583-589.
Petit, J.R., Jouzel, J., Raynaud, D., Barkov, N.I., Barnola, J.-M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V.M., Legrand, M., Lipenkov, V.Y., Lorius, C., Pepin, L., Ritz, C., Saltzman, E., and Stievenard, M. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436.
Smagorinsky, J., Bryan, K., Manabe, S., Armi, L., Bretherton, F.P., Cess, R.D., Gates, W.L, Hansen, J. and Kutzbach, J.E. (Eds.). 1982. Carbon Dioxide and Climate: A Second Assessment. National Academy Press, Washington, DC.
Yokoyama, Y., Lambeck, K., Deckker, P.D., Johnston, P. and Fifield, L.K. 2000. Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406: 713-716.