It's not unstoppable, it's just gonna be fairly hard to tackle.
Nuclear fusion *might* come sooner than we're expecting. Lockheed Martin has a project which is hoping to have a by 2017, commercial by 2022. I'd say that's ridiculously hopeful, except for the fact that it's Lockheed Martin, who are otherwise known as a ridiculously clever bunch of engineers - exactly the sort of people that you'd want to be solving fusion. It is, however, worth noting that they haven't said anything about this project since announcing it to the public this time last year.
CO2 scrubbers are theoretically possible, but they will eat energy. Plants do it by a form of solar power, but we need it on a scale much larger considering the backlog of CO2 that we've pumped out since the Industrial Revolution. So before we can start scrubbing the atmosphere, we need to get the Energy Industry off fossil fuels. In the short term, pumping stratospheric-aerosols into the atmosphere would reflect sunlight and help lower the global temperature, but we don't know the long term consequences.
Nuclear Fission is a good stopgap solution. We know that Fusion will get here sooner or later, at which point we can stop producing Nuclear Waste - and in any case, Nuclear Waste is a long term problem. CO2 is a much shorter term problem. However, Nuclear Fission is rather unpopular. (Because nobody likes the word Nuclear. Blame the Cold War and the A-Bomb.)
Renewables are also a good solution, which are much more popular than Nuclear Fission. However, Renewables are unpredictable. You can't tell the wind when to blow, and you can't the sun when to shine. So we need to be able to efficiently store energy, and we need smart grids to be able to manage the highly fluctuating supply and demand.
Overall, the world's problem is an over-reliance on fossil fuels. They're unhealthy and polluting even without the Global Warming problem - smog, oil spills, and some fairly nasty chemicals along for the ride. CO2 is the mouldy cherry on the rotten cake.
BUT there is, actually, a fairly bright future. Eventually. The day we get fusion working, and working well, the world will change. Energy becomes essentially free when your fuel is water, and your waste product is helium. Try to imagine a world where energy is free and available to all. It'll take us a while to get there, and even when we do, the world won't change overnight, but I can believe it will happen.
However, in the short term, yeah, we're screwed. Unpredictable weather, rising sea levels, potential food shortages, and probably an economic collapse if we run out of fossil fuels before we've changed the energy infrastructure. The next century might not be that pleasant...
The short term good news is that the growth of CO2 output year-on-year has finally started slowing. Which shows that we are making some progress, even if its not much.
PS: Since this is a video game website, and it's a related topic, I highly recommend Fate of the World as an educational game on Global Warming. It's essentially an Earth Sim from 2020 to 2220, with some pretty impressive work having been put into the simulator. It does, however, have a brutally difficult learning curve.
