CO2 concentrations have risen from 310 ppm to 410 ppm since the 1930s. However, there has been no net change in Arctic or Greenland temperatures during these last 90 years. During the Pliocene, CO2 also ranged between about 300-400 ppm, but the Arctic was 15-22°C warmer and sea levels 25 meters higher than today. Is CO2 really Earth’s “control knob”?
Nearly ten years ago, the imagery of a CO2 “control knob” for climate was canonized in the journal Science.
The CO2 concentration was said to determine – or control – Earth’s temperature.
However, the scientific literature’s paleoclimate record does not provide fundamental support for this paradigm of a CO2-controlled climate.
During the Ordovician, for example, CO2 concentrations reached 4,200 ppm – more than 10 times today’s levels. And yet the Earth returned to a glaciated “Snowball Earth” state during this period (Shuang et al., 2019).