( However ( , ( ( melting rates ) ( ( ( ( ( ( ( are ( increasingly significant ) ) , ) especially ) ( at ( lower altitudes ) ) ) , ) ( suggesting ( ( a ( major increase ) ) ( in ( summer ( air temperature ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (NP (NN melting) (NNS rates)) (VP (VBP are) (ADJP (RB increasingly) (JJ significant)) (, ,) (ADVP (RB especially)) (PP (IN at) (NP (JJR lower) (NNS altitudes))) (, ,) (VP (VBG suggesting) (NP (NP (DT a) (JJ major) (NN increase)) (PP (IN in) (NP (NN summer) (NN air) (NN temperature)))))) (. .)))
However, melting rates are increasingly significant, especially at lower altitudes, suggesting a major increase in summer air temperature.
(ROOT (S (NP (NNP Air) (NN temperature)) (VP (VBZ changes) (PP (IN as) (NP (NN altitude) (NNS increases)))) (. .)))