( ( Some scientists ) ( ( believe ( that ( ( ( the ( CO 2 ) ) ( released ( by ( human activities ) ) ) ) ( is ( ( ( enhancing ( the ( greenhouse effect ) ) ) and ) ( contributing ( to ( ( an increase ) ( in ( ( the ( earth 's ) ) ( overall temperature ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT Some) (NNS scientists)) (VP (VBP believe) (SBAR (IN that) (S (NP (NP (DT the) (NNP CO) (CD 2)) (VP (VBN released) (PP (IN by) (NP (JJ human) (NNS activities))))) (VP (VBZ is) (VP (VP (VBG enhancing) (NP (DT the) (NN greenhouse) (NN effect))) (CC and) (VP (VBG contributing) (PP (TO to) (NP (NP (DT an) (NN increase)) (PP (IN in) (NP (NP (DT the) (NN earth) (POS 's)) (JJ overall) (NN temperature))))))))))) (. .)))
Some scientists believe that the CO 2 released by human activities is enhancing the greenhouse effect and contributing to an increase in the earth's overall temperature.
(ROOT (S (NP (NNP Human) (NNS actions)) (VP (VBZ has) (VP (VBN increased) (NP (DT the) (NN greenhouse) (NN effect)))) (. .)))