Our civilization was not possible until the Earth warmed up, warmer than today, roughly 10,000 years ago.
We are in an ice age right now. It is a inter-glacial warm period, but still an ice age. Whenever this period ends and it cools back down, that is when the true disaster will emerge as the carrying capacity will rapidly fall and mankind will be fighting what is left. Starvation will become extremely common.
The period known as the The Little Ice Age had major effects but nothing compared to what entering another period of glaciation will bring.
About 10,000 or so years ago, the Earth had warmed up enough for mankind to begin settling down in agricultural communities instead of consisting in small bands of subsistence hunters. Our distant ancestors were finally able to take some control over their lives instead of just moving from place to place looking for prey.
Coupled with this was the accidental development of the modern hexaploid wheat during the same rough time period. Before that, we only had diploid and tetraploid wheat. Some unknown farmer sowing his ancient crop of wheat accidentally included a related grass. By horizontal gene transfer, the genes from the related grass entered that tetraploid wheat and voila, it has 42 chromosomes instead of the previous 28 chromosomes. This new wheat quickly spread across Europe and Asia and eventually around the world. The tetraploid wheats are still important today for things like pasta, but the wheat that enabled civilization to flourish like never before was the hexaploid wheat that was successfully grown around the world.
Prior to our current interglacial warm period, sea levels were about 100 meters lower than now. Just a few thousand years ago, they were about two meters higher than today because of the warmer temperatures of that time.
If you want to see the probable end of our civilization, cool it back down. That can happen pretty quickly, too. There is some thought that when we entered the cool period known as The Younger Dryas, we dropped about 10 degrees Centigrade over a few years. The knowledge that this will almost certainly happen again along with the uncertain knowledge of when it will happen is what is truly scary.