What do you get when you combine an aging population with a weakening economy? Well, what do you think?
And lest you think that climate change can be at most an inconvenience, empires have fallen for far less. Civilization as we know it depends on highly productive agricultural and distribution systems, which are in turn sensitive to climate parameters. Failure to mitigate long-term climate change and adapt our food production systems to the climate change already unavoidable will result on massive political upveals of the un-fun kind (try to imagine a functioning modern democracy with chronically inadequate food supplies) , and an untold number of deaths.