( It ( ( is ( caused ( mostly ( by ( ( increasing concentrations ) ( of ( ( greenhouse gases ) ( in ( the atmosphere ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (VP (VBN caused) (PP (RB mostly) (IN by) (NP (NP (VBG increasing) (NNS concentrations)) (PP (IN of) (NP (NP (NN greenhouse) (NNS gases)) (PP (IN in) (NP (DT the) (NN atmosphere))))))))) (. .)))
It is caused mostly by increasing concentrations of greenhouse gases in the atmosphere.
(ROOT (S (NP (JJS Most) (NNS scientists)) (VP (VBP agree) (SBAR (IN that) (S (NP (NP (DT an) (NN increase)) (PP (IN in) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN greenhouse) (NNS gases)) (VP (VBG entering) (NP (NP (NN earth) (POS 's)) (NN atmosphere)))))))) (VP (VBZ causes) (NP (NP (DT an) (NN increase)) (PP (IN in) (NP (NP (NN melting)) (PP (IN of) (NP (JJ polar) (NN ice) (NNS caps)))))))))) (. .)))
Most scientists agree that an increase in the amount of greenhouse gases entering earth's atmosphere causes an increase in melting of polar ice caps.