The Kalahari desert spreads across Botswana, engulfing the capital in sand dunes, and driving millions of refugees out to surrounding countries.
A permanent El Nino grips the Pacific, causing weather chaos around the world, and drought in the Amazon.
The whole Amazonian ecosystem collapses in a conflagration of fire and destruction – desert and savannah eventually take over where the world’s largest rainforest once stood.
Huge amounts of carbon pour into the atmosphere, adding another degree to global warming. Water runs short in Perth, Sydney and other parts of Australia away from the far north and south.
Hurricanes strike the tropics half a category stronger than today’s, with higher windspeeds and rainfall.
Agriculture shifts into the far north – Norway’s growing season becomes like southern England is today. But with declines in the tropics and sub-tropics due to heat and drought, the world tips into net food deficit.
The Indus river runs dry due to glacial retreat in the Himalayas, forcing millions of refugees to flee Pakistan.
Possible nuclear conflict with India over water supplies.
Notes from Mark Lynas author of Six Degrees: Our Future on a Hotter Planet
Three Degrees video description from National Geographic