[std_throwaway]

Money spent = Emissions generated (direct or indirect by further spending)

If you want to save CO2, then save as much money as you can in paper form. Don't spend, don't invest. Instead keep everything as cash. This also has indirect effects by slowing down the economy which reduces money flow for other people, too.

[baroffoos]

You can spend your money on digital goods which have a very tiny environmental impact. This doesn't have the result of preventing other people from spending that money but it is at least sustainable if everyone does it.

[timwaagh]

Indeed. We keep chasing our own tail. It's largely pointless.