For something like spending or calories, you probably have to cut back under 20% or under 10%, and even that is hard enough on its own.
Trying to simply cut back for CO2 needs something like a 90% reduction to actually solve things. It could theoretically work but it very quickly hits diminishing returns and becomes a bad allocation of effort. Projects like actively replacing all our power plants, and making sure all cars have a minimum electric range, are much more "low hanging fruit" than trying to directly cut consumption that far.
Trying to simply cut back for CO2 needs something like a 90% reduction to actually solve things. It could theoretically work but it very quickly hits diminishing returns and becomes a bad allocation of effort. Projects like actively replacing all our power plants, and making sure all cars have a minimum electric range, are much more "low hanging fruit" than trying to directly cut consumption that far.