Myth: Carbon dioxide levels only rose after the start of warm periods, so CO₂ does not cause warming

Samples of ice dating back hundreds of thousands of years have been extracted from the sheets covering Antarctica and Greenland. These cores show that at the end of recent ice ages, the level of CO₂ in the atmosphere often did not start to rise until temperatures had already been climbing for some time. There is uncertainty about the precise timing, partly because the air trapped in the cores is younger than the ice itself, but it appears the lags might sometimes have been 800 years or more.