If we don't treat the really high-carbon fuels as off-limits, we may well be heading for up to 5 degrees Celsius of warming by the end of this century. In case you don't realize it, that's an "extinction event."
The target we hear so much about is 2C. The goal our leaders have set is to cut greenhouse gas emissions enough to limit warming by 2 degrees Celsius. We don't think much about what a 2C world would be like but we should. We should have a solid grasp on that reality because 2C still leaves us in a survival mode world.
What follows is taken from the 2009 Stern Report. Grim as it sounds, research in the years since has demonstrated this is actually quite understated. Still, it's a good starting point for head-clearing.
2C – The temperature limit the scientists want
The heatwaves seen in Europe during 2003, which killed tens of thousands of people, will come back every year with a 2C global average temperature rise. Southern England will regularly see temperatures around 40C in summer. 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 lifeforms. 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 West Antarctic ice sheet collapses, the Greenland ice sheet melts and the world's sea level begins to rise by seven metres over the next few hundred years. Glaciers all over the world will recede, reducing the fresh water supply for major cities including Los Angeles. Coastal flooding affects more than 10 million extra people. A third of the world's species will become extinct as the 2C rise changes their habitats too quickly for them to adapt.
3C – Looking increasingly likely
After a 3C 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 1.5C. 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. Around 30-50% less water is available in Africa and around the Mediterranean. In the UK, summers of droughts are followed by winter floods. Sea levels rise to engulf small islands and low-lying areas such as Florida, New York and London. The Gulf Stream, which warms the UK all year round, will decline and changes in weather patterns will lead to higher sea levels at the Atlantic coasts.
4C - Possible with an extremely weak deal
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. At the Arctic itself, the ice cover would disappear permanently, meaning extinction for polar bears and other native species that rely on the presence of ice. 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 50C in summer. Southern England's summer climate could resemble that of modern southern Morocco.
5C and above – Highly unlikely nightmare scenario
With a 5C rise, global average temperatures would be hotter than for 50m years. The Arctic region sees temperatures rise much higher than average – up to 20C – meaning the entire Arctic is now ice-free all year round. Most of the tropics, sub-tropics and even lower mid-latitudes are too hot to be inhabitable. The sea level rise is now sufficiently rapid that coastal cities across the world are largely abandoned. Above 6C, there would be a danger of "runaway warming", perhaps spurred by release of oceanic methane hydrates. Could the surface of the Earth become like Venus, entirely uninhabitable? Human population would be drastically reduced.
Notice how 5C was dismissed as "highly unlikely"? That part of it has been dropped from current scenarios. In the Arctic the tundra and underlying permafrost are already being impacted. Tundra is drying out, catching fire and we're powerless to put out these fires. They result in black soot, a good bit of which gets deposited on the Greenland ice sheet accelerating melting. As the tundra burns the permafrost beneath melts and collapses, releasing stored methane. At the time of the Stern Report we thought this sort of thing was still decades off.
The reality is that the 2C target was really just the limit for adaptation. There were means for some advantaged countries to adapt to the impacts, albeit not without a good deal of economic and social dislocation. We still talk 2C but those who maintain that fantasy often turn out to be the same politicians intent on maximizing extraction of our massive fossil fuel reserves.
To help get some idea of 2C consider that we're already dealing with early-onset climate change impacts and we're just at 0.8C over pre-industrial temperatures.
Yet other than politicians who would just like the whole business to go away, few climate scientists believe we have any hope of 2C and we're more probably looking at 4C or worse.
2C, 4C, 5C - forget about it. It's a distraction. What you need to focus on is the point that, no matter how much warming is already "locked in" we can ensure that the future is far more dangerous than necessary if we don't sequester high-carbon fossil energy just as quickly as possible. A recent study by the World Bank concluded that we've already locked in warming of 1.5C for our grandkids even if we completely decarbonize our economies and our societies today. Yet, despite already bequeathing our grandchildren a truly miserable environment, our fossil fuel consumption and greenhouse gas emissions continue to increase year after year. Every tonne of CO2 we emit to the atmosphere simply adds to that 1.5C future.
Sure choosing life over fossil energy is going to be calamitous. Our stock markets are inflated with energy stocks the value of which is premised on fossil fuel reserves at fictional market values. There are many trillions of dollars of unrealizable carbon assets on our markets. You can't simply write off that much notional wealth without massive economic fallout. The upheaval is going to be painful, especially for those with portfolios stuffed with energy stocks and bonds. Yet that's a small price to pay for avoiding extinction. A small price indeed.