Failing to limit the global temperature to 1.5C above pre-industrial levels could trigger tipping points and lead to the collapse of life on Earth, two climate scientists have warned.
Opening the Innovation Zero Congress in London, Professors Johan Rockstrom and David King said our current path will lead us to certain disaster, destroying rainforests and marine life while making vast areas around the tropics uninhabitable for humans.
The Intergovernmental Panel on Climate Change has said that current climate policies will leave the Earth between 2.5C and 2.7C hotter by 2100 compared with pre-industrial levels.
It has already warmed by 1.2C, with the World Meteorological Organisation warning there is a two-thirds chance of scientists recording a 1.5C temperature sometime in the next five years – although for now, only temporarily.
UN member states pledged in the Paris Agreement in 2015 to limit temperature rise to below 2C and to strive for 1.5C.
Prof Rockstrom of the Potsdam Institute for Climate Impact Research, said: “1.5C is not a target. I call it a physical limit.
“There’s one conclusion without any uncertainty whatsoever, and that is that 2.5C global mean surface temperature rise is a disaster.
“It’s something that humanity has absolutely no evidence that we can cope with. It would actually exceed the warmest temperature on Earth over the past four million years.
“Push ourselves to 2.5C – we’re in unknown terrain. It would lead to a complete melting of the big ice sheets, which would be a 10 metre sea level rise.
“There would be a collapse of all the big biomes on planet Earth – the rainforest, many of the temperate forests – abrupt thawing of permafrost, we will have complete collapse of marine biology, we will have a shift of large parts of the habitability on Earth.
“Over one-third of the planet around the equatorial regions will be uninhabitable because you will pass the threshold of health, which is around 30C.
“It’s only in some parts of the Sahara Desert today that has that kind of average temperature.
“So in summary, it’s a place we do not want to go to. The problem is, we’re following that path today.”
He also said that how the Earth’s natural systems behave after 1.5C is unknown and that it will likely trigger five tipping points which would see the Earth heat uncontrollably towards disaster.
Three of these tipping points are in the Arctic, which is heating up four to five times faster than the rest of the Earth, Prof King, chair of the Centre for Climate Repair at the University of Cambridge, said.
The five tipping points identified are: melting of the West Antarctic and Greenland ice sheets, melting of permafrost in the far north, mass die-off of tropic coral reefs and melting sea ice in the Bering Sea.
Prof Rockstrom said: “The big fear that we have in science is when you cause tipping points, when the system goes from self-cooling to self-warming.
“Today we’re the ones causing the warming but the nightmare is of course, the moment the planet itself starts causing the warming and that’s what we under all circumstances have to avoid.”
Asked if he had a magic wand to summon whatever change he would like to see, Prof King said he wishes the Earth’s natural systems were treated as importantly as human ones and that we learn to remove greenhouse gases from the atmosphere at scale while refreezing the polar regions and Himalayas.
He added: “That 1.5C target is a must. If we don’t stay below that, frankly, the talk about going up to 2C then bringing the temperature down by removing greenhouse gases, that is not good enough.
“Too many people will die in that period when we allow the temperatures to go up.”