It's not about fixing what has already been destroyed and what will be destroyed regardless at this point, but about minimizing the losses.
We should do whatever is in our best ability to slow down global warming and limit it's impact on the ecosystem.
Why minimize the effects when we can prevent it? Yes at this point in our lives it will be very hard for people to adjust to what we were used to but unless we change our habits that hurt the environment, adjust our lifestyle then we might as well just pack our emergency bags and prepare for the worst.