In a stark new warning, the world’s leading climate scientists have shown that global warming must be kept to a maximum of 1.5C to lessen the risk of drought, floods, extreme heat and poverty for hundreds of millions of people.
“We can see there is a difference and it’s substantial,” Roberts said.
At 2C extremely hot days, such as those experienced in the northern hemisphere this summer, would become more severe and common, increasing heat-related deaths and causing more forest fires.
Sea ice-free summers in the Arctic, which is warming two to three times fast than the world average, would come once every 100 years at 1.5C, but every 10 years with half a degree more of global warming.
Reforestation is essential to all of them as are shifts to electric transport systems and greater adoption of carbon capture technology.
Carbon pollution would have to be cut by 45% by 2030 – compared with a 20% cut under the 2C pathway – and come down to zero by 2050, compared with 2075 for 2C.
The report will be presented to governments at the UN climate conference in Poland at the end of this year.
At the current level of commitments, the world is on course for a disastrous 3C of warming.
But he said opinion had shifted in the past few years along with growing evidence of climate instability and the approach of tipping points that might push the world off a course that could be controlled by emissions reductions.
It has a scientific robustness that shows 1.5C is not just a political concession.