National Greenhouse Gas Emissions Inventory Act of 2003

National Greenhouse Gas Emissions Inventory Act of 2003 - Amends the Clean Air Act to require the Administrator of the Environmental Protection Agency to establish and administer: (1) a national greenhouse gas emissions information system to collect annual lists required to be submitted under this Act of an entity's greenhouse gas emissions; and (2) a national greenhouse gas registry (included in such system) to collect voluntarily reported information on emissions reductions. Specifies factors for adjustment of emissions records by a reporting entity.