( ( ( ( ( ( Subsiding air ) ( is ( ( compressed ( by ( ( the ( increasing pressure ) ) ( of ( the ( surrounding air ) ) ) ) ) ) ( as ( it descends ) ) ) ) ) , ) so ) ( ( the air ) ( ( warms up ) ( as ( it subsides ) ) ) ) ) . )
(ROOT (S (S (NP (VBG Subsiding) (NN air)) (VP (VBZ is) (VP (VBN compressed) (PP (IN by) (NP (NP (DT the) (VBG increasing) (NN pressure)) (PP (IN of) (NP (DT the) (VBG surrounding) (NN air))))) (SBAR (IN as) (S (NP (PRP it)) (VP (VBZ descends))))))) (, ,) (IN so) (S (NP (DT the) (NN air)) (VP (VBZ warms) (PRT (RP up)) (SBAR (IN as) (S (NP (PRP it)) (VP (VBZ subsides)))))) (. .)))
Subsiding air is compressed by the increasing pressure of the surrounding air as it descends, so the air warms up as it subsides.
(ROOT (S (SBAR (IN As) (S (NP (DT a) (NN diver)) (VP (VBZ descends)))) (, ,) (NP (NP (DT the) (NN increase)) (PP (IN in) (NP (NN pressure)))) (VP (VBZ causes) (NP (NP (DT the) (NN body) (POS 's)) (NN air) (NNS pockets)) (PP (IN in) (NP (NP (DT the) (NNS ears) (CC and) (NNS lungs)) (PP (TO to) (NP (NNS compress)))))) (. .)))