In any climate change there are winners and losers. By returning to a Ordovician weather we are opening up a lot of arable land, and plant growth will benefit greatly (or bigly, if you wish). Species who rely on colder climes —polar bears, penguins, alpine meadows — may disappear forever. Whole ecosystems will be overturned and reordered. Chances are, it’ll look a lot less like Blade Runner 2049 and more like Jurassic Park.
Now, mankind evolved during the present Ice Age. We are a hardy species, but we’ve never been tested like this before. Will we adapt or die? Only time will tell.