You swap a plentiful greenhouse gas for another greenhouse gas that is burnable at no net environmental cost.

Methane synthesized from excess renewable power can store that renewable power for years, handily fixing the whole "Sun don't shine every day" problem.

It's durable energy storage and can be easily moved around like liquid fuels.

It also would remove CO2 emissions from things like airplanes, which won't be able to be battery powered in the near future, and could renewably replace chemical feedstocks in lots of industrial processes.

But this requires immense industrial capability, probably some serious innovation in absorbing CO2 from the atmosphere because that's basically an unsolved problem right now, and a massive oversupply of solar power which cannot happen under market systems because nobody builds infrastructure to sell power at below market rates.

It might be a 50 year plan.