( ( ( ( ( Air pollution ) , ) ( in turn ) ) , ) ( ( causes ( ( ( ( ( ( acid rain ) , ) ( ozone depletion ) ) , ) and ) ( global warming ) ) ) . ) )
(ROOT (S (NP (NP (NNP Air) (NN pollution)) (, ,) (PP (IN in) (NP (NN turn))) (, ,)) (VP (VBZ causes) (NP (NP (JJ acid) (NN rain)) (, ,) (NP (NN ozone) (NN depletion)) (, ,) (CC and) (NP (JJ global) (NN warming)))) (. .)))
Air pollution, in turn, causes acid rain, ozone depletion, and global warming.
(ROOT (S (NP (JJ Acid) (NN rain)) (VP (MD may) (VP (VB be) (VP (VBN caused) (PP (IN by) (NP (NN air) (NN pollution)))))) (. .)))