It used to be the case that scientists had a good theory about what weather there would be in different seasons, and this theory was usually right. They couldn't predict daily weather all that well, but they could predict that you could reasonably grow oranges in Florida without worrying about it being colder than Maine for a week and snowing a month later, and they could tell you that there would be snow in Vancouver and not in Dallas.
Now conditions are outside the boundaries that climate models are based on, and scientists really have no clue any more. And it's not just the scientific climate models that don't apply; common sense and experience are no longer relevant, because we don't have history that tells us what happens in this environment, measured, anecdotal, or otherwise. In all of our past experience, the arctic wind has blown eastwards around the pole. Then one year it blows across the pole into Europe. Two years later, it blows across the pole into North America. Is this going to be a regular occurrence? Nobody knows.
The extent to which climate change has a falsifiable hypothesis, it is rejecting the null hypothesis. That is, you can ask: is the environment now following the patterns we have previously observed? We find that we are observing patterns that we had not observed previously, including some that we would have noticed had they occurred in a substantial time period. On the other side, we've previously been able to demonstrate enough of an understanding of climate to know how to build houses and what crops to plant where. But the evidence that you should build houses in Florida to keep heat out and houses in Maine to keep heat in is getting less certain. The issue is not that scientists know that something bad is going to happen, it's that nobody has any clue if something bad is going to happen, even after taking into account that some bad things never happened before, because the situation is just different in some measurable ways.
Personally, my guess is that the planet has major negative feedback, or it wouldn't have stayed in a reasonably narrow range of climates long enough for life to get this far. More greenhouse gasses in the atmosphere will trigger more cooling by some other mechanism, which might be okay or might be all of the continents turning into highly-reflective deserts instead of light-absorbent arable land. We really can't make an accurate prediction.