We don't know for certain. Right now, based on evidence we've accumulated, we believe that we're in a rare temperate plateau between normally hot and cold extremes, and that we're accelerating in a slide towards the hot state.
This is all based on large amounts of inference. It could be completely wrong, but right now it matches the accumulated evidence to the best of our ability to compare and analyze.
Of course, just because you know your world model may be faulty, doesn't mean you should live your life catering to the possible faultiness. In other words, just because you can hedge your bets on your belief doesn't mean you should hedge your actions. I recognize that there's an outside chance that I may be hallucinating the chair in front of my computer desk right now, but I'm still going to sit on it without even pausing. :)