Real Climate and others like to use the “CO2 doubling rule” to calculate climate sensitivity.  Every doubling of CO2 is supposed to produce something like 2.5C temperature rise.

That tells us that Venus is about 29 degrees warmer than Earth. Only off by 400+ degrees.

Obviously the high temperatures on Venus are not due to the greenhouse effect, yet our clueless friends (followers of Sagan) keep on insisting that it is.