If we today, immediately, stabilize our level of greenhouse gases, we still have half a degree of warming in store. We've had one degree of warming—it's actually slightly less—and it's half of that again. It's committed, no matter what, even if we immediately stabilized emissions.
We've looked at these experiments. Some have argued that the time scale for carbon dioxide is 50 to 200 years in the atmosphere. It turns out, actually, that as you saturate more and more in the atmosphere, that time scale becomes longer and longer. So if we were to ask the question what happens if we burn our existing known resources of carbon—where does the atmosphere stabilize, and can we draw it down, if we burn our known reserves of carbon, 5,000 petagrams of carbon—we're going to end up with CO2 levels stabilizing at 700 to 800 parts per million, and the drawn-down time from that is on the time scale of tens of thousands of years; that is, the system becomes saturated.
So the answer to your question is, we have warming in store for centuries no matter what we do. The question becomes, what do we want the path of society to end up in? Do we want to end up in an Easter Island type of scenario, or do we want to end up in one that's more sustainable?