The federal tax code provides preferential treatment for the production and use of renewable energy. We report estimates of the subsidies' effects on greenhouse gases (GHG) emissions developed in a recent National Research Council (NRC) Report. Due to lack of estimates of the impact of tax provisions on GHG emissions, new modeling studies were commissioned. The studies found, at best, a small impact of subsidies in reducing GHG emissions; in some cases, emissions increased. The NRC report also identified the need to capture the complex interactions among subsidies, pre-existing regulations, and commodity markets.