CO2 traps the heat in the atmosphere and then this heat is transferred to the oceans which act like batteries for heat year around

The more people burn oil and wood and everything else and the more herds of animals they maintain for food, the more CO2 and Methane will harm the atmosphere and the more ice will melt even at the north and south poles. So, everyone will have to get used to getting water more from oceans where droughts replace rain while other areas will get even more rain because warmer air can hold higher and higher amounts of water which then will cause flooding some places and severe droughts other places around the world. 

So, people have a choice of being flooded out or migrating because of severe droughts worldwide often. So, water is either too much or not enough many or most places on earth as a direct result of increasing heat in the atmosphere of earth over time. Then the winds are a problem too. Winds blow away animals and humans and plants which means eventually topsoil will also blow away like in the dustbowl of places like Oklahoma in the 1930s in movies like "Grapes of Wrath".

Migrations of millions of people which we are seeing here now from Central America where crazy weather is often not raining enough or too much and washing away whole communities.

So, only those cultures that are highly technologically educated and organized can continue to survive what we are all facing now worldwide this century.