You don’t know that emissions will only start to fall when the “population begins to fall”. That’s just a wild guess on your part.

To get where we need to go, we will need a decline in lifestyle

This only makes sense if you’re a millionaire. You’re completely missing sight of whose “lifestyles” are fucking us over. The Pentagon is one of the biggest polluters in the world. Oil companies have coated the earth in micro plastics. But you think a “decline in lifestyle” is needed to improve the environment?