( ( ( ( ( The ( main ( greenhouse gas ) ) ) , ) CO2 ) , ) ( ( comes ( from ( ( the burning ) ( of ( fossil fuels ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ main) (NN greenhouse) (NN gas)) (, ,) (NP (NNP CO2)) (, ,)) (VP (VBZ comes) (PP (IN from) (NP (NP (DT the) (NN burning)) (PP (IN of) (NP (JJ fossil) (NNS fuels)))))) (. .)))
The main greenhouse gas, CO2, comes from the burning of fossil fuels.
(ROOT (S (NP (JJ Co2) (NN gas)) (VP (VBZ is) (VP (VBN released) (PP (IN into) (NP (NP (DT the) (NN atmosphere)) (SBAR (WHADVP (WRB when)) (S (NP (JJ fossil) (NNS fuels)) (VP (VBP are) (VP (VBN burned))))))))) (. .)))