Evidence from ice cores
Another significant reversal for the supporters of cuts to human emissions of CO2 has come about through more detailed analysis of ice cores from the Greenland Ice Cap, and from several stations in Antarctica. Many climate alarmists have claimed that those observations actually proved that anthropogenic CO2 emissions were responsible for 20th-century global warming. But 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. 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. 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. It is clear from these ice cores that the increase in CO2 could not be the main cause of the increase in temperature, but that it is a consequence of that increase in temperature. What happens is that first, the rocks on the land begin to warm. Gradually, the increasing warmth affects the ocean. And as the ocean warms, it gives off more CO2.