Underwater when sea level rises less than a foot a century? Get serious. Cold kills way more than heat. Death from extreme weather has been largely mitigated by industrialization and modern technology. Increased food production from more CO2 has helped reduce starvation.
Please, show me one genuine climate refugee right now.
That's a function of growing population in poor areas to live (flood plains, dessert). Changing CO2 concentration to deal with this is about the least effective way I can imagine to help these areas.
There are a number of pacific islands such as the Marshall islands, Kiribati and a number of others. Majuro (the main island of the Marshall islands had a population of 20 thousand in 2012, but is currently only 6' above sea level. 1' of sea level rise removes the majority of the land, and already significant number of climate refugees from these islands who have resettled to other areas.