( ( Ocean acidification ) ( ( is ( ( the ( ongoing decrease ) ) ( in ( ( ( ( the pH ) ( of ( ( the ( Earth 's ) ) oceans ) ) ) , ) ( ( caused ( by ( ( the uptake ) ( of ( ( carbon dioxide ) ( -LRB- ( CO2 -RRB- ) ) ) ) ) ) ) ( from ( the atmosphere ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Ocean) (NNP acidification)) (VP (VBZ is) (NP (NP (DT the) (JJ ongoing) (NN decrease)) (PP (IN in) (NP (NP (DT the) (NN pH)) (PP (IN of) (NP (NP (DT the) (NN Earth) (POS 's)) (NNS oceans))) (, ,) (VP (VBN caused) (PP (IN by) (NP (NP (DT the) (NN uptake)) (PP (IN of) (NP (NP (NN carbon) (NN dioxide)) (PRN (-LRB- -LRB-) (NP (NNP CO2)) (-RRB- -RRB-)))))) (PP (IN from) (NP (DT the) (NN atmosphere)))))))) (. .)))
Ocean acidification is the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2 ) from the atmosphere.
(ROOT (S (NP (NNP Ocean) (NNP acidification)) (VP (VBZ occurs) (SBAR (WHADVP (WRB when)) (S (NP (NP (JJ excess) (NN carbon) (NN dioxide)) (PP (IN in) (NP (DT the) (NN atmosphere)))) (VP (VBZ causes) (S (NP (DT the) (NNS oceans)) (VP (TO to) (VP (VB become) (NP (NNS acidic))))))))) (. .)))
Ocean acidification occurs when excess carbon dioxide in the atmosphere causes the oceans to become acidic.