this comes with a cost. nbc's lee cowan starts us off tonight from l.a. lee, good evening. >> reporter: well, brian, this ends debate that lasted nearly a decade about auto pollution that started right here on the roads of california. now that these so-called clean car standards are going to be mandatory across the board, it makes it the first time ever the federal government limited greenhouse gas emissions. it was 1975 when the government first put fuel economy standards in place, back when cars looked like land boats and got 13 miles to the gallon. >> you get more power. >> reporter: technology made cars a lot less thirsty, but the average auto's appetite is too much for the white house. so by 2014, the government will mandate cars and light trucks bump their average up to over 35 miles a gallon it's projected over the lifetime of those newly-regulated vehicles, carbon dioxide emissions will be reduced by 960