Earlier research in this journal suggests that nuclear power systems have prevented 1.84 million air pollution-related deaths from 1971 to 2009 and could save an additional 7 million deaths by 2050. Building on that work, we adopt a broader lens that looks at renewable energy and nuclear power as well as a greater range of energy pathways. We examine via 10 hypothetical scenarios and two time frames the varying impact of different technology configurations on the full potential of avoided carbon emissions and avoided mortality across China, the European Union, India, and the United States. From 2000 to 2020, we estimate the substitution of fossil fuels by nuclear power has saved as many as 42 million lives. Similarly, substituting fossil fuels with hydropower has saved 42.1 million lives (slightly more than that for nuclear power). Finally, other forms of renewable energy have saved another 38 million lives . We project that from 2021 to 2040, nuclear power could save an additional 46.1 million lives and displace 1198 GtCO2; hydropower could save a further 46.2 million lives and displace 1281.47 GtCO2; substituting fossil fuels with other renewable energy could similarly save an additional 41.2 million lives as well as displace over 1250 GtCO2. We offer a critical thought experiment on just how much potential low-carbon options have to provide positive externalities compared to fossil fuels.