The development of hydrogen technologies for powering light duty vehicles and stationary loads is primarily motivated by the problem of greenhouse gas (GHG) emissions. The expected cost of a transition to a hydrogen infrastructure causes some to reject hydrogen and look to more incremental changes to reduce emissions. This study shows that the potential for reducing GHG emissions from two energy sectors, light-duty vehicles and electricity generation, is limited by the fact that their combined contribution to current U.S. emissions is about half the total. A linear projection of U.S. GHG emission data to 2050 suggests that yearly emissions will increase by 70% over 1990 emissions. Incremental improvements to eliminate carbon dioxide emissions will struggle to overcome growth over the next four decades. The study considers proposed changes to the U.S. Corporate Averaged Fuel Economy (CAFE) regulation to predict a reduction in GHG emissions of only 8-10%. In the electricity sector, replacing America’s coal-fired power with natural gas can reduce the overall GHG emissions by nearly 30%. Together, these incremental changes will only overcome the estimated growth by mid-century. Further reductions below 1990 emissions will require carbon-free technologies and fuel supply, suggesting hydrogen should be considered. Transition periods used in this analysis suggest that 2050 is sufficient time for the transition to a new fleet of light-duty vehicles to be completed; however, unless power plants are to be retired before their design life, it will be difficult to complete a transition in the electricity sector by mid-century.