It's simple: CO2 greenhouse effect is proven, the concentration of CO2 is measured and is increasing, the temperature is measured and is increasing. Clever science can figure out even CO2 concentrations and temperatures of the times when nobody measured.

https://en.m.wikipedia.org/wiki/Ice_core

The expected rise of CO2 closely matches our fosil fuels consumption.

https://www.skepticalscience.com/human-co2-smaller-than-natu...