( We ( ( know ( ( ( ( that ( ( human activities ) ( ( have substantially ) ( ( ( increased ( ( the concentration ) ( of ( carbon dioxide ) ) ) ) ( in ( the atmosphere ) ) ) ( during ( the ( past ( two centuries ) ) ) ) ) ) ) ) , ) and ) ( that ( ( carbon dioxide ) ( is ( one ( of ( ( the ( ( most important ) contributors ) ) ( to ( the ( atmospheric ( ` ( greenhouse effect ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP know) (SBAR (SBAR (IN that) (S (NP (JJ human) (NNS activities)) (VP (VBP have) (ADVP (RB substantially)) (VP (VBN increased) (NP (NP (DT the) (NN concentration)) (PP (IN of) (NP (NN carbon) (NN dioxide)))) (PP (IN in) (NP (DT the) (NN atmosphere))) (PP (IN during) (NP (DT the) (JJ past) (CD two) (NNS centuries))))))) (, ,) (CC and) (SBAR (IN that) (S (NP (NN carbon) (NN dioxide)) (VP (VBZ is) (NP (NP (CD one)) (PP (IN of) (NP (NP (DT the) (ADJP (RBS most) (JJ important)) (NNS contributors)) (PP (TO to) (NP (DT the) (JJ atmospheric) (`` `) (NN greenhouse) (NN effect))))))))))) (. .)))
We know that human activities have substantially increased the concentration of carbon dioxide in the atmosphere during the past two centuries, and that carbon dioxide is one of the most important contributors to the atmospheric 'greenhouse effect.
(ROOT (S (NP (NNP Human) (NNS actions)) (VP (VBZ has) (VP (VBN increased) (NP (DT the) (NN greenhouse) (NN effect)))) (. .)))