Monthly average carbon dioxide amounts in the atmosphere (light purple line) at NOAA's Mauna Loa Observatory since 1958. Amounts are shown in parts per million (ppm): the number of carbon dioxide molecules per million molecules of dry air. The dark purple line is the 12-month rolling average.

The amount of carbon dioxide in the atmosphere during ice ages and warm periods over the past 800,000 years, based on Antarctic ice core data (Lüthi, D. et al, 2008). On this time scale, the increase to 2021’s 414.7 parts per million (dark purple dot) looks practically instantaneous.