Impacts on early Mars can produce H2 and CH4 in the thermal plume. In a thick CO2 atmosphere, collision‐induced absorptions between CO2‐H2 and CO2‐CH4 can boost the greenhouse effect. We construct a simple model of the impact history of Mars and show that for a variety of impactor types and CO2 surface pressures >0.5 bars, postimpact surface temperatures due to H2 alone can exceed the melting point of water for much longer periods of time than from the dissipation of the heat derived from the impactor's kinetic energy. This longer timescale is set by hydrogen escape rather than radiation to space. Cumulatively, the Noachian surface may have been above the melting point of water for millions of years by this mechanism. These greatly extended postimpact warm environments may have played a larger role in the erosion and mineralogy of the surface than previously thought and may partly explain some of the observed fluvial features. Plain Language Summary: We propose that meteorites could warm ancient Mars by degassing H2 into a thick CO2 atmosphere after they impact the surface. The impact creates a hot thermal plume where water oxidizes the meteorite's reduced materials producing H2 gas in the process. Collisions between CO2 and H2 molecules enhances the greenhouse effect and warms the surface. If the impactor is large enough in diameter (>100 km), surface temperatures can rise above freezing for many thousands of years—a time scale much longer than previously envisioned. This mechanism must have operated to some degree and could partly explain the observed erosion, fluvial features, and mineralogy of ancient Martian surfaces. Key Points: Reductants in meteorites oxidized by water and CO2 can produce significant quantities of CO and H2 in the thermal plume following an impactDegassing of H2 following a large impact could warm Mars above the melting point for tens to hundreds of thousands of yearsDuring the Noachian epoch the total time for above‐melting surface temperatures could have been millions of years [ABSTRACT FROM AUTHOR]