(S (S (S (NP (EX There)) (VP (VP (VBZ is) (PRN (COMMA ,) (S (BASENP (PRP he)) (VP (VBZ says))) (COMMA ,))) (NP (NP (JJ enough) (NP (NP (BASENP (NN land)) (COMMA ,) (BASENP (NN water))) (CC and) (BASENP (JJ human) (NN capacity)))) (S (VP (TO to) (VP (VP (VB produce) (NP (BASENP (JJ enough) (NN food)) (PP (IN for) (BASENP (DT a) (JJ growing) (NN population))))) (PP (IN over) (BASENP (DT the) (JJ next) (NN 50) (NNS years))))))))) (CONJP (COMMA ,) (CC but)) (S (NP (BASENP (NN one)) (PP (IN of) (BASENP (DT the) (NNS challenges)))) (VP (VBZ is) (S (VP (TO to) (VP (VP (VP (VB provide) (BASENP (JJ enough) (NN water))) (PP (IN for) (BASENP (NN agriculture)))) (PP (IN without) (S (VP (VBG damaging) (BASENP (DT the) (NN environment))))))))))) (PERIOD .))