It's what we know will happen because of...science...ffs.
There's a huge amount of variables when it comes to future warming and what will happen to our environment. It's possible to wager an educated guess on what may likely happen but it's impossible to predict precisely what will happen, besides more obvious things like rising water levels and ice melting. There's too many variables that interact with each other to know with precision. Models on warming go by projections and probabilities, like any projections do.
That's why it's hard to accurately predict the weather beyond a few days...too many interacting variables. If one variable changes it can have a cascading effect causing a change in everything else. Also why it's hard to predict how a ie: baseball player will perform next year despite 10 years of prior data to go off of. Age, injuries, opponents, teammates, coaches, contracts, personal circumstances, weather, etc are some of the many variables that can all change making projection models impossible to be accurate, but probabilities of what's most likely to occur are possible.