The way CO2 is working make that its GH effect grow with altitude. And while C02 is heavier than O2 and N2, convection and probably other boring effects (i fail

The way CO2 is working make that its GH effect grow with altitude. And while C02 is heavier than O2 and N2, convection and probably other boring effects (i failed my thermodynamic classes, and it was 10 years ago, sorry) makes that the Co2 surplus emitted at sea level will find itself in high troposphere in 20 to 30 years. So the effect we have right a this moment is mostly caused by the carbon we emitted in early 2000's and before.