( ( In ( ( year 's ) past ) ) ( ( the ( air temperatures ) ) ( ( ( have steadily ) ( dropped ( as ( the ( altitude increases ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (NP (NN year) (POS 's)) (NN past))) (NP (DT the) (NN air) (NNS temperatures)) (VP (VBP have) (ADVP (RB steadily)) (VP (VBN dropped) (PP (IN as) (NP (DT the) (NN altitude) (NNS increases))))) (. .)))
In year's past the air temperatures have steadily dropped as the altitude increases.
(ROOT (S (NP (NNP Air) (NN temperature)) (VP (VBZ changes) (PP (IN as) (NP (NN altitude) (NNS increases)))) (. .)))