Five Degrees

Five degrees of warming is the same magnitude of change as at the height of the last ice age, when it was five degrees colder and much of Europe and North America were buried under ice sheets. This makes it hotter on the planet now than at any time for 55 million years in the past. At 5 degrees C we can expect:

Desert belts expand from the subtropics into temperate regions.
Civilisation collapses as humanity is unable to cope.
Some nations try to shift their populations towards the poles.
Might the US invade Canada and China invade Siberia?
Methane hydrate release and associated tsunamis push warming into a further spiral.
Most of the world is uninhabitable.

Notes from Mark Lynas author of Six Degrees: Our Future on a Hotter Planet

Five Degrees video description from National Geographic