Does increased atmospheric CO2 cause warming?
For over 60 years we have reliable records of levels of atmospheric CO2 and temperature.
We also have estimates of temperature and atmospheric CO2 obtained using ice core measurement methods. These enable us to analyse the relationship from earlier times.
What do those records tell us about the relationship between atmospheric CO2 and temperature?
Note, however, that we are looking for the effects of human activity, so there is no reason to go back farther in time, as human activity that would significantly and adversely affect the level of atmospheric CO2 only started at about the time of the 2nd Industrial Revolution.
Global average temperature vs CO2 1959-2023
Annual average global temperature anomaly values were obtained from Our World in Data.
Atmospheric CO2 values were obtained from NASA.
Plotting these produces the chart shown.
The coefficient of correlation over the period 1959-2023 is over 96%.
That is strong correlation.
Global average temperature vs CO2 1880-2023 (using ice core data)
Annual average global temperature anomaly values were obtained from Our World in Data.
CO2 values were obtained from NASA.
Plotting these produces the chart shown.
The coefficient of correlation over the period 1880-2023 is over 95%.
That is also strong correlation.
Carbon dioxide before mankind
For more information about the heat-trapping effects of CO2 see this NASA page.
Another useful chart is the one shown here, which makes the point that for millennia carbon dioxide levels have not been near current levels. CO2 levels were higher much longer ago, but that was well before mankind evolved, so mankind has never lived on Earth with CO2 levels higher than they are now.