How do we know that?
Why, it's because of what those sooper dooper computer climate models tell us! That makes it true, don't you know?
"Yes, kids, science is a wonderful thing. But not nearly as wonderful as climate modeling, which can perform supernatural miracles. Honest! Climate modeling can raise the level of the oceans (even without Obama's intervention), it can burn up the planet a hundred years from now, and Shazzam! -- the models can save us again -- all without leaving your video games, and without the benefit of the real-world data that you need for boring old regular science."
It's a MIRACLE, I tell you, a MIRACLE!
Wait, what do you mean, "you don't believe it"?
What are you, some kind of knuckle dragging, fringe science, non-peer reviewed, non "scientific consensus" denier?