That's if _everyone_ withdraws. That's not what's happening. 0.3 degrees is if the US withdraws but everyone else proceeds as planned. But we aren't even withdrawing per se. Immediately after announcing his decision, Trump also announced his willingness to re-negotiate the accords on better terms (by which I think he means not spending $100/B a year on something that other countries aren't even legally bound by).

And climate models predict things just fine as long as you pick the ones that are somewhat accurate in retrospect. That's not what prediction is. Prediction is when, like Al Gore, you say that in 15 years we'll all be underwater, and it doesn't happen. If you bet your money on the accuracy of the current models you will lose.