( This ( ( means ( that ( ( air pressure ) ( decreases ( with ( increasing altitude ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ means) (SBAR (IN that) (S (NP (NN air) (NN pressure)) (VP (VBZ decreases) (PP (IN with) (NP (VBG increasing) (NN altitude))))))) (. .)))
This means that air pressure decreases with increasing altitude.
(ROOT (S (NP (NNP Air)) (VP (VBP pressure) (SBAR (S (NP (PRP it)) (VP (VBZ decreases) (PP (IN as) (NP (NN altitude) (NNS increases))))))) (. .)))