Even without climate change, anthropogenic or otherwise, our own destruction of habitat coupled with lack of responsibility in controlling birth rates will bring down most of civilisation. Humanity will become like the horse at the beginning of the 20th century, only the sudden decline in population will likely be more brutal and devastating. The broad, multiple discipline accepted notion is that the population will peak at 2050 and then decline..but it may be much sooner thanks to the climate factors adding to the death spiral. In the US alone over 35% of food crops were lost this year due to the weather..and that's merely supplemental to over farming and resource depletion.

According to some theorists the population will naturally decline by over 90% while the fringes say it's over and we're already extinct, just waiting to die. The reality is, likely half of us will simply not have grandchildren for one reason or another, and 3 out of 4 of us will not have descendants living past 2100.