[gooserock]

Rising sea levels are a concern in the long-term, but what I'm most worried about in my lifetime is the collapse of the industrial food system due to rapid warming.

Basically if the Earth warms faster than plants and science can adapt, it's a real possibility that a very large chunk of the arable land that currently feeds eight billion people worldwide will become useless. The fear is that we won't be able to grow wheat or rice where we used to, due to heat and drought (Great Plains) or floods (Southeast Asia) or whatever else.

Sure, we could just start farming Siberia and Northern Canada, but it would take decades to establish all the infrastructure necessary to do that, and in the meantime we'd have to deal with truly massive famines, political destabilization, and the collapse of many states. Not to mention the fact that crop yields will inevitably be lower in arctic latitudes due to shorter growing seasons.

Our entire civilization is built on a global, industrial food network, and it's more precarious than you think. Most countries don't have reserves of food at all, and the ones that do only have scant reserves. If methane releases cause the Earth's climate to lurch warmer in a short enough period of time, a couple real good crop failures will cause the network to collapse, and our civilization (or at least a few entire regions) will collapse in short order.