Something to think about... The mystery of similar planets

Assume we have two planets, and everything about them is the same- orbit, size, etc. Except for one thing. Their atmosphere. Planet A has an atmosphere that is two miles tall; We'll assume this atmosphere has an average density of 100 air molecules per cubic inch. Next, we have planet B, with an atmosphere of density 10,000 air molecules per cubic inch. This atmosphere, however, is ten times lower than planet A. So, planet b's atmosphere, as compared to planet a, is thinner. However, it is also denser at the same time. So, the question now is: how will the planets' climate differ?