Final answer:
Coal is the non-renewable resource that is the worst emitter of CO2, and substituting coal with natural gas can reduce CO2 emissions as it burns cleaner.
Step-by-step explanation:
The non-renewable resource that is the worst emitter of carbon dioxide is coal. Coal, when burned, releases roughly twice as much CO₂ per unit of delivered energy compared to other fossil fuels like natural gas and crude oil. Switching from coal to natural gas would significantly reduce carbon emissions because natural gas produces less CO₂ per energy unit than coal. Although uranium used for nuclear power is a nonrenewable resource, its main concern is the disposal of radioactive waste, but unlike the burning of fossil fuels, it does not produce CO₂ as a direct byproduct of energy generation.