You're talking about undoing already released CO2.
The people discussing mitigation are talking about decreasing the release rate of new CO2, so the peak value or the value a hundred years from now can be smaller.
Your math is right but you're solving the wrong equation.
If humans all disappeared right now and CO2 stayed at 400ppm approximately forever, you're treating that as the "failure" case. Everyone else is treating 400ppm as a mild success, and their "failure" cases are far far higher levels like 1000ppm.
If your goal is a binary "not get punched in the face" then it's too late after you get hit a couple times. But it still makes a big difference whether they stop after a few punches, or keep going until you're in the hospital!
The people discussing mitigation are talking about decreasing the release rate of new CO2, so the peak value or the value a hundred years from now can be smaller.
Your math is right but you're solving the wrong equation.
If humans all disappeared right now and CO2 stayed at 400ppm approximately forever, you're treating that as the "failure" case. Everyone else is treating 400ppm as a mild success, and their "failure" cases are far far higher levels like 1000ppm.
If your goal is a binary "not get punched in the face" then it's too late after you get hit a couple times. But it still makes a big difference whether they stop after a few punches, or keep going until you're in the hospital!