( but ( ( when ( ( ( the ( earth 's ) ) surface ) ( ( ( reradiates energy ) back ) ( to space ) ) ) ) ( , ( ( ( a ( significant portion ) ) ( of ( this ( thermal radiation ) ) ) ) ( ( is ( ( ( ( absorbed and ) ( ( reradiated ( ( by ( ( the ( atmosphere 's ) ) ( CO2 molecules ) ) ) back ) ) ( to ( ( the ( earth 's ) ) surface ) ) ) ) , ) ( incrementally ( warming ( the planet ) ) ) ) ) . ) ) ) ) )
(ROOT (S (CC but) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT the) (NN earth) (POS 's)) (NN surface)) (VP (VBZ reradiates) (NP (NN energy)) (PRT (RP back)) (PP (TO to) (NP (NN space)))))) (, ,) (NP (NP (DT a) (JJ significant) (NN portion)) (PP (IN of) (NP (DT this) (JJ thermal) (NN radiation)))) (VP (VBZ is) (VP (VP (VBN absorbed)) (CC and) (VP (VBN reradiated) (PP (IN by) (NP (NP (DT the) (NN atmosphere) (POS 's)) (NN CO2) (NNS molecules)) (ADVP (RB back))) (PP (TO to) (NP (NP (DT the) (NN earth) (POS 's)) (NN surface)))) (, ,) (S (ADVP (RB incrementally)) (VP (VBG warming) (NP (DT the) (NN planet)))))) (. .)))
but when the earth's surface reradiates energy back to space, a significant portion of this thermal radiation is absorbed and reradiated by the atmosphere's CO2 molecules back to the earth's surface, incrementally warming the planet.
(ROOT (S (NP (NP (NNS Gases)) (PP (JJ such) (IN as) (NP (NN co2) (CC and) (NN methane)))) (VP (MD can) (VP (NN trap) (NP (NP (JJ thermal) (NN energy)) (PP (IN in) (NP (NP (NN earth) (POS 's)) (NN atmosphere)))) (PP (IN before) (S (VP (VBG radiating) (NP (PRP it)) (PP (IN into) (NP (NN space)))))))) (. .)))