Sea level rise has big effects

Probability: 90%

Timeline: 25 years

This one seems to be a no-brainer. Just quickly reading the Wikipedia entry about sea level rise show this to be very likely.

The real questions to consider at this point are:

1. How fast will it happen?
2. What areas will be impacted the most?

Certainly low-lying island nations are most at risk. In fact, large parts of Tuvalu have already been evacuated and the entire country may eventually have to be abandoned!

How well can coastal populations deal with a 1-meter rise in sea levels by the end of the century? We'll have to see.