Do hybrid cars result in a net reduction of carbon footprint?

After all they are made in factories [using petroleum] the batteries are made in factories [using petroleum] and even though they allegedly "sip" gasoline, recent changes to fuel formulations have made all vehicles less efficient [thanks to corn based ethanol] and when the battery packs die, the cost of replacement is prohibitive to resale value... therefore no p along "trade-in" Greener?