Climatologists have long used ice core samples from Greenland to measure climate changes over the last hundred thousand years or so. But according to the BBC, a group of scientists under the banner of the European Project for Ice Coring in Antarctica, or EPICA, managed to pull a three kilometer-long ice core from Antarctica, revealing the pattern of climate change over the past 740,000 years. By studying gases trapped in the ice, these cores can tell us a great deal about changes to the temperature and atmospheric composition for much of the last million years.
The BBC article gives a good summary, but the article in the June 10 issue of Nature is available here (PDF). The article is brief, but informative. One of the interesting take-aways is the conclusion that the current "inter-glacial era" we live in is likely to go on, absent human disruption, for another 15,000 years, due to the position of the Earth's orbit. Most previous inter-glacials lasted no more than 10,000 years (and it's been about 12,000 years since the last ice age). The last time we saw a long-duration inter-glacial era was around 420,000 years ago; that one lasted for 28,000 years.
A more troubling bit of information from the research concerns CO2 levels. There is a very strong correlation of CO2 concentrations and average air temperature. At the peak of the previous similar inter-glacial period, CO2 concentrations increased to around 275-280 parts per million by volume (ppmv), up from a minimum of 200 ppmv in the previous glacial era. Measurements of CO2 concentrations on Mauna Loa from 1958 to 1998 show a growth of CO2 levels from 316 ppmv to 369 ppmv (it's a bit higher now). While we've known for awhile now that current CO2 levels are much higher than in the pre-industrial period, this is the first time we've been able to measure CO2 concentrations for such an extended period of time, and directly compare them to the last long-period inter-glacial era.
I just ran some quick numbers and using the 200 carbon number as the base during the last glacial period, the 280 as the peak in the last inter-glacial period is a %40 increase while the current 369 is a %80 increase.. in other words our carbon is twice as much now then it was at the height of the last period we were similair too .. and it is growing yearly. In addition to the other green house gases that are present now that were probably not present back then it could be even more.
I am still left with the impression that if you press hard enough on the light switch eventually it will flip, carbon might be applying more pressure than the earths position to the sun. It is comforting to know that the earth-sun variable may not be in play but there are others to factor such as the global dimming effect.