The best way to reduce emissions of CO2, is to develop sources of energy that are more economical than fossil fuels. If we had the huge surpluses of carbon emissions free energy implied by fusion, we'd be able to slash energy-related carbon emissions to a small fraction of the current level, while also drastically reducing the need to extract hydrocarbons as a chemical feedstocks. Fusion is probably even capable of providing enough energy to sequester excess carbon, beyond emissions.
Fusion energy is not free. The cost of building a reactor alone puts the price in the same range as fission. But it's safer, and we have an abundance of fuel for it. So build it to handle base loads, use wind/solar where it makes sense, and use excess production to some meaningful task.
