Glacial-interglacial CO2
Considerable effort has gone into creating, calibrating and testing each of the proxies discussed here. Proxies for atmospheric CO2 have a unique strength in that they can be tested against the ice-core CO2 record based on ancient samples of atmosphere trapped in ice up to 800 thousand years old.
Over glacial-integlacial cycles, boron-derived CO2 reconstructions (panel A) fall within ±25 ppm of the ice-core CO2 record. Alkenone-derived CO2 reconstructions (panel B) show lower sensitivity to glacial-interglacial CO2 variability, but exhibit lower CO2 levels during glacial maxima and a more gradual decline in interglacial levels.
