Well, the so called terraforming was science fiction for a very long time but recently scientist started believing it's actually possible.

The Problem is you don't have just to warm it for a few degrees but for a quite a bit.

earth's medium temp is 288 K whereas the Martian is only 210 K

Also the differences in pressure are significant.

They think the terraforming will take several thousands of years, to create a similar base as on the earth of 3.5 billion years ago when cyanobacteria started producing oxygen.