I was talking Celsius / Kelvin. I'm assuming the speaker was referring to Fahrenheit - I'm thinking mankind as a whole might be able to survive +8 degree K iff we find efficient synthetic food sources that work in such a climate (which I assume we will) - however it would probably be at a fraction of the population we have today - whether our civilization could survive an indirect genocide on a global scale to have the infrastructure to do this is another question.
edit: re your edit: if it's true that +6 degrees sets perpetual heating mechanisms in motion which lead to +12 degrees by 2300 (as suggested in the ted talk), yes, we probably wouldn't survive +8 in the long run. it's damn scary, really - if we screw this up in the next 20 years, we basically damn the whole planet.
I meant Celsius, but see my edit - I have to revise that guess. Given that +6 degree C will probably cause runaway warming processes to initiate (which I wasn't thinking about before), surviving for even a few more centuries suddenly becomes a tough order.
edit: re your edit: if it's true that +6 degrees sets perpetual heating mechanisms in motion which lead to +12 degrees by 2300 (as suggested in the ted talk), yes, we probably wouldn't survive +8 in the long run. it's damn scary, really - if we screw this up in the next 20 years, we basically damn the whole planet.