Is the current rise in CO2 definitely caused by human activities?

        September 19, 2018 Scripps Institution of Oceanography | Global | fossil fuels: emissions

A known amount of CO2 is produced from burning fossil fuels, either absorbed in the oceans, taken up by plants, or left in the atmosphere. About 57% has remained in the air, increasing the level to over 400 ppm (N2, O2, Ar, ... and CO2 gases mix easily). The level was higher millions of years ago from natural processes, but the recent increase is not natural.