( Humans ( ( ( may not ) ( be ( ( the cause ) ( of ( global warming ) ) ) ) ) ; ) )
(ROOT (S (NP (NNS Humans)) (VP (MD may) (RB not) (VP (VB be) (NP (NP (DT the) (NN cause)) (PP (IN of) (NP (JJ global) (NN warming)))))) (: ;)))
Humans may not be the cause of global warming;
(ROOT (S (NP (NNP Human) (NNS beings)) (VP (VBP is/are) (NP (NP (DT the) (JJ main) (NN cause)) (PP (IN of) (NP (JJ recent) (JJ global) (NN warming))))) (. .)))
Human beings is/are the main cause of recent global warming.