One Degree
Deserts invade the High Plains of the United States, in a much worse repeat of the 1930s dustbowl. Whilst the epicentre is Nebraska, states from Canada in the north to Texas in the south suffer severe agricultural losses. Mount Kilimanjaro loses all its ice. The Gulf Stream switches off – perhaps, plunging Britain and Europe into icy winter cold. Irreversible feedbacks take hold in the Arctic as ice disappears, and the permafrost line shifts north. Rare species wiped out in the Queensland rainforest, Australia. Coral reefs around the world suffer increasing losses from bleaching and are wiped out. Coral atolls submerge under the rising seas.
Two Degrees
Oceans turn increasingly acidic, wiping out calcareous plankton and further hitting surviving coral reefs – much of the marine food chain endangered. One summer in every two has heatwaves as strong as the 2003 disaster in Europe, when 30,000 died. Drought, fire and searing heat strikes the Mediterranean basin. Greenland tips into irreversible melt, accelerating sea-level rise and threatening coastal cities around the world. Hundreds of millions live in peril of the rising seas. Polar bears, walrus and other ice-dependent marine mammals extinct in the Arctic. Glaciers in Peru disappear, threatening water supplies to Lima. Declining snowfields also threaten water supplies in California. A third of species worldwide face extinction as the climate changes – the worst mass extinction since the end of the dinosaurs.
Three Degrees
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.