How much has atmospheric CO2 changed since the industrial and agricultural revolutions?
When snow falls it traps air. In polar and other regions where the snow never melts it eventually forms ice and this air is entrained in tiny bubbles. Typically about 100 mls of air are contained in every 1 kg of ice. Thus polar ice acts as a kind of an “air museum” providing us with information on the composition of the atmosphere up to more than half a million years ago in the past. Extraction and gas analysis techniques tell us what the concentrations of CO2 were in the atmosphere before 1950. In addition they overlap the direct atmospheric measurements since the 1950s and confirm the present rate of increase. CO2 concentrations measured from ice collected at Law Dome glacier in the Antarctic show that atmospheric CO2 has been remarkably constant at about 270 to 280 ppm over about the last 1000 years until the 18th century when it began to rise. As of 2005, the level had risen to 378 ppm, an increase of 35%. On the basis of ice core records the current CO2 concentrations are unprece
