> But is it even possible to sustain this many people (at
   > current standards of living with foreseeable technology)?

Absolutely, there is a tremendous amount of waste which is not recaptured due to economic rather than technological reasons. Further there are technologies (like nuclear power and breeder reactors) which can provide energy forever (for all practical purposes). And ultimately the survival of humans can be reduced to simply to energy, energy to grow food, energy to process wastes, and energy to communicate and interact. Modern nuclear submarines stay submerged under the ocean for 6 months, only coming up for consumables such as food. A companion "farm" sub (not that such a thing currently exists, but is certainly possible given the extent of aquaculture today) could provide the necessary consumable. Letting the submarine pair exist under the ocean until its nuclear fuel ran out. Add a third submarine that has a breeder reactor and a fuel reprocessing pipeline and you've got a permanent colony.

It still requires Newport News to build more subs but you get the picture. With enough energy you can support the entire predicted population of the planet.

But emotionally, there are bigger problems. Nation states and large population groups are at risk of starvation and deprivation as a direct result of climate change. And those at risk populations are not getting any support from the people who are putatively putting them at risk. So emotionally, an existential crisis is probably justified.