Between one and two degrees warming nobody will think of Mediterranean holidays. The movement from northern Europe to the Mediterranean is likely to reverse, switching eventually into a mass movement as Saharan heatwaves sweep across the Mediterranean. People everywhere will think twice about moving to the coast. Coastal communities will suffer.

As mountains lose their glaciers, people will lose their water supplies. The Indian subcontinent will be fighting for survival. As the glaciers disappear, their runoff will cease to power the massive rivers that deliver freshwater to hundreds of millions. Water shortages and famine will be the result, destabilising the entire region.

Between two and three degrees warming, preventing mass starvation will be unavoidable. First millions, then billions, will face an increasingly tough battle to survive. All soils will be affected by the rising heat, but none as badly as the Amazon’s.

Catastrophe is too small a word for the loss of the rainforest. It produces 10% of the World’s entire photosynthetic output from plants. Drought and heat will cripple it; fire will finish it off. In Human terms, the effect on the planet will be like cutting off oxygen during an asthma attack.

New super-hurricanes grow from the warming sea, salt water will creep up the stricken rivers, poisoning ground water. Higher temperatures mean greater evaporation, further drying out vegetation and soils, and causing huge losses from reservoirs. In state capitals, heat every year is likely to kill between 8,000 and 15,000 mainly elderly people.

As the mountains lose their snow, so cities and farms will lose their water and dried-out forests and grasslands will perish. All of Human history shows that, given the choice between starving and moving, people move. In the latter part of the century tens of millions of may be facing this choice.

Between three and four degrees warming, the stream of refugees will now include those fleeing from coasts to safer interiors – millions at a time when storms hit. Where they persist, coastal cities will become fortified islands. The World economy, will be threadbare, direct losses, social instability.

China is on a collision course with the planet. China’s agricultural production will crash. It will face the task of feeding 1.5bn much richer people – 200m more than now – on two thirds of current supplies. For people throughout much of the World, starvation will be a regular threat.

Air-conditioning will be mandatory for anyone wanting to stay cool. This in turn will put ever more stress on energy systems, which in turn pour more greenhouse gases into the air and gas-fired power stations ramp up their output, hydroelectric sources dwindle and renewables fail to take up the slack. 

One of the most dangerous of all feedbacks will now be kicking in – the runaway thaw of permafrost. At least 500 billion tonnes of carbon are waiting to be released from the Arctic ice. If we reach three degrees, that leads inexorably to four degrees, which leads inexorably to five degrees.

Between four and five degrees warming, we are looking now at an entirely different planet. Ice sheets have vanished from both poles; rainforests have burnt up and turned to desert; the dry and lifeless Alps resemble the High Atlas; rising seas are scouring deep into continental interiors.

Populations from dry areas move to the newly thawed regions of the far north, in Canada and Siberia. Even here, though, summers may be too hot for crops to be grown away from the coasts; and there is no guarantee that northern governments will admit southern refugees.

Siberia and Canada will be invaded by China and the US, each hammering another nail into humanity’s coffin. Any armed conflict, will further increase the planetary surface area uninhabitable for Humans.

Globalism will break down into something like parochialism. Customers will have nothing to buy because producers will have nothing to sell. With no possibility of international aid, migrants will have to force their way into the few remaining habitable enclaves and fight for survival.

Where no refuge is available, civil war and a collapse into racial or communal conflict seems the likely outcome. Survivalism will turn into a further disaster for biodiversity as hungry Humans kill and eat anything that moves. Including, perhaps, each other.

Invaders do not take kindly to residents denying them food. History suggests that if a stockpile is discovered, the householder and his family will be tortured and killed.

Between five and six degrees warming, 95% of species are wiped out, an episode worst ever endured by life on Earth, the closest the planet will come to ending up a dead and desolate rock in space. On land, the only winners are fungi that flourish on dying trees and shrubs. At sea there are only losers. Warm water is a killer.

Beneath the oceans, another monster stirrs, Methane hydrate. Unlike CO2, methane is flammable. The ultimate nightmare, with oceanic methane eruptions near large population centres wiping out billions of people – in days. Burnt survivors battling over food, wandering far and wide from empty cities.

Then would come hydrogen sulphide from the stagnant oceans, it will be a silent killer. As the ozone layer came under assault, we will feel the sun’s rays burning into our skin, and the first cell mutations would be triggering outbreaks of cancer among anyone who survived.

Dante’s hell was a place of judgment, where humanity was for ever punished for its sins. With all the remaining forests burning, and the corpses of people, livestock and wildlife piling up in every continent, the six-degree World would be a harsh penalty.

For the mundane crime of burning fossil energy.