The volcanic activity has already started globally and its a slow burn. It's time frame will depend on how fast the last of the old ice melts away on both poles allowing for the chain reaction to occur. Mother nature will make mans over use and abuse and fuse igniting look like a puff of smoke, then we will begin a huge cool down and the glaciers will return.
Remember NM has 1000+ "dormant volcanoes" and they are currently practicing Emergency Preparedness. I'll simplify my approach to the response We will need to bend over grab our ankles and kiss our ass goodbye! The first to exit will be the luckiest. We are at 400 + ppm CO2 the last time earth was at this level was 800,000 years ago. Do the math and you'll find the solution quicker.