I once had a site promoting that which I thought at the time would be sustainable and nice; Earthship Villages. Built and lived in by intelligent strong people, with some having enough capability to manufacture batteries, solar panels, generators, inverters, and other power equipment to use. Plus the ability to protect themselves from hostile outside groups.
Growing their own food, recycling everything, keeping the population constant or near so. Growing in the Earthships, using aquaponics, raising rabbits, chickens, outside grain and woods, with pasture, orchards--- a regular utopia, connected to other villages by radio or satellite. The sum total of human knowledge with each village. Kind of a high tech agrarian society with bartering food, manufactured items, education, labor, and child care.
That was before I found out about the probability of going worse than PETM. Then I thought of underground fortresses with GenIV nuclear grow lights, a good aquifer, and similar living arrangement except underground.
The outside villages would eventually lose all their outside growing, unless they went nomadic toward the poles. Even then time would run out for them. As it would for those underground who would have no survivable surface for two hundred thousand years.
So one hope is to reduce emissions 90% within a decade and hope as we live through momentum and the 400 year cool down, almost all after a rapid die-off period.
Another hope is for a geologic incident which reduces population through economic meltdown or loss of a season of growing globally.
Another possibility is limited nuclear war that takes out the 500 biggest cities. Some have thought a pandemic could also do it.
Katla(South Icelandic volcano) is due, so is La Palma and the Cascadia Rip. As a geology guy for life, I would say they are more likely than the others in preventing the AETM ELE.
Either way of the several, it won't be an easy ride for people or many other life forms on Earth. Like the calm before the storms of my grandchildren, if my son has one. But he knows what is ahead, too. If I would have not had excessive hope in 1987, he probably never would have been born. Now, I am sorry for what man has done to this biosphere, and I feel for the children of the future. Crying out over the annals of time, those who could have been.
http://www.youtube.com/watch?v=9xbpgmJCxT8