( This ( ( is ( because ( ( most ( of ( our electricity ) ) ) ( is ( produced ( by ( ( ( ( burning ( fossil fuels ) ) ( -LRB- ( ( particularly coal ) -RRB- ) ) ) , ) ( which ( ( ( ( is , ) ( in turn ) ) , ) ( ( the ( major source ) ) ( of ( ( carbon dioxide ) ( in ( the atmosphere ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (SBAR (IN because) (S (NP (NP (JJS most)) (PP (IN of) (NP (PRP$ our) (NN electricity)))) (VP (VBZ is) (VP (VBN produced) (PP (IN by) (NP (NP (NP (VBG burning) (NN fossil) (NNS fuels)) (PRN (-LRB- -LRB-) (NP (RB particularly) (NN coal)) (-RRB- -RRB-))) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (, ,) (PP (IN in) (NP (NN turn))) (, ,) (NP (NP (DT the) (JJ major) (NN source)) (PP (IN of) (NP (NP (NN carbon) (NN dioxide)) (PP (IN in) (NP (DT the) (NN atmosphere)))))))))))))))) (. .)))
This is because most of our electricity is produced by burning fossil fuels (particularly coal), which is, in turn, the major source of carbon dioxide in the atmosphere.
(ROOT (S (NP (NNP Coal)) (VP (VBZ is) (NP (NP (DT the) (NN source)) (PP (IN of) (NP (JJS most) (NN electricity))))) (. .)))