Yes, it's an unfounded hoax. And there isn't even any correlation between the CO2 level and temperature! https://www.mdpi.com/2225-1154/5/4/76/htm   4. ... Correlation does not imply causality, but the absence of correlation proves conclusively the absence of causality. The finding that atmospheric CO2 concentration and ΔRFCO2 are generally uncorrelated with T, therefore, implies either that neither variable exerted significant causal influence on T during the Phanerozoic Eon or that the underlying proxy databases do not accurately reflect the variables evaluated.