After a 1°C global average temperature rise, arctic sea ice would disappear for good in the summer months. Heatwaves and forest fires will become more common in the sub-tropics. The worst hit will be the Mediterranean region, southern Africa, Australia and south-west United States. Most of the world’s corals will die, including the Great Barrier Reef. Glaciers that provide crops for 50 million people with fresh water begin to melt and 300,000 people are affected every year by climate-related diseases such as malaria and diarrhoea.
With a 2°C global average temperature rise the Amazon turns into desert and grasslands, while increasing CO2 levels in the atmosphere make the world’s oceans too acidic for remaining coral reefs and thousands of other marine life forms. More than 60 million people, mainly in Africa, would be exposed to higher rates of malaria. Agricultural yields around the world will drop and half a billion people will be at greater risk of starvation. The world’s sea level begins to rise by seven metres over the next few hundred years. Coastal flooding affects more than 10 million extra people. A third of the world’s species will become extinct.
After a 3°C global temperature rise, global warming may run out of control and efforts to mitigate it may be in vain. Millions of square kilometres of Amazon rainforest could burn down, releasing carbon from the wood, leaves and soil and thus making the warming even worse, perhaps by another 1.5°C. In southern Africa, Australia and the western US, deserts take over. Billions of people are forced to move from their traditional agricultural lands in search of scarcer food and water.
At this stage, the Arctic permafrost enters the danger zone. The methane and carbon dioxide currently locked in the soils will be released into the atmosphere. Further melting of Antarctic ice sheets would mean a further 5m rise in the sea level, submerging many island nations. Italy, Spain, Greece and Turkey become deserts and mid-Europe reaches desert temperatures of almost 50°C in summer.