The last IPCC climate change report predicted that shits gonna get real fucking bad for a while, but at the rate we're going it should at least turn around sometime between 80 to 100 years.
We could shut of all fossil fuel usage tomorrow except for where it's needed (eg a single generator to kick start a countries power grid if things actually go down) and make a painful hard switch to renewables. We could begin using renewable energy sources to start extracting CO2 from the atmosphere.
I don't know and can't speak to how effective that would be, from memory the earth would continue to warm for some time to come even on their optimistic predictions.