( We ( ( know ( that ( ( human activity ) ( ( ( has ( increased ( ( the concentrations ) ( of ( these molecules ) ) ) ) ) and ) ( has ( enhanced ( the ( greenhouse effect ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP know) (SBAR (IN that) (S (NP (JJ human) (NN activity)) (VP (VP (VBZ has) (VP (VBN increased) (NP (NP (DT the) (NNS concentrations)) (PP (IN of) (NP (DT these) (NNS molecules)))))) (CC and) (VP (VBZ has) (VP (VBN enhanced) (NP (DT the) (NN greenhouse) (NN effect)))))))) (. .)))
We know that human activity has increased the concentrations of these molecules and has enhanced the greenhouse effect.
(ROOT (S (NP (NNP Human) (NNS actions)) (VP (VBZ has) (VP (VBN increased) (NP (DT the) (NN greenhouse) (NN effect)))) (. .)))