The CO2 is determined from analysis of ice bubbles. (realclimate.org)
Climate researchers use these proxies, chemical signals locked in minerals and ice bubbles as well as pollen and other biological indicators, as indirect measures of temperature and precipitation patterns in the distant past. (giss.nasa.gov)
If the spirits didn't get you, the dry ice bubbling away in your glass would... public liability must have been way less intense back then... Occasionally we'd head to Sydney for the weekend to dance at The Exchange on Oxford Street. (housegoeshome.com)