( Thompson ( ( ( is skeptical ) ( that ( ( global warming ) ( is ( ( caused primarily ) ( by ( human activities ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Thompson)) (VP (VBZ is) (ADJP (JJ skeptical)) (SBAR (IN that) (S (NP (JJ global) (NN warming)) (VP (VBZ is) (VP (VBN caused) (ADVP (RB primarily)) (PP (IN by) (NP (JJ human) (NNS activities)))))))) (. .)))
Thompson is skeptical that global warming is caused primarily by human activities.
(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.