The Earth is getting hotter and the fault lies with humans – Adam Vaughan

Within the next twenty years, the Earth will inevitably reach the critical threshold of global warming, with temperatures rising by 1.5 degrees due to climate change, even if governments around the world have to radically reduce gas emissions. greenhouse.

This was stated in the report on the climate situation agreed on 6 August by 196 countries and made public on 9 August by the Intergovernmental Panel on Climate Change (IPCC), which defined the role of human beings in causing climate change as “unequivocal”, a very stronger than the adjective “clear” used eight years ago.

The researchers pointed out that each of the past four decades has been progressively warmer than any previous decade since the 1850s, and pointed out that without a sharp reduction in emissions there will be an increase in extreme weather events. 2021 has already been marked by devastating floods and heat waves, from Canada to China. “Climate change is not a problem of the future, it is a problem of the present and affects every region of the world,” explains Friederike Otto of the University of Oxford, one of the main authors of the IPCC.

In the worst of five scenarios for the future evolution of global emissions, the world would face a catastrophic average temperature increase of 4.4 degrees by 2100. In all five scenarios, the average temperature increase over the next twenty years compared to the pre-industrial period will reach or exceed the threshold of 1.5 degrees, the more ambitious limit set in the 2015 Paris Accords, which also included the objective of keeping warming within two degrees.

The good news is that in the best-case scenario, if net emissions were zeroed out and removed from the atmosphere, global warming would drop to 1.4 degrees by 2100. “Targets of 1.5 or two degrees are not the best. edges of a precipice, ”explains Ed Hawkins of the British University of Reading, one of the authors of the IPCC report. “Crossing that threshold does not mean that we are plunging towards the abyss. Every slightest variation is important. But the consequences worsen as the temperature rises. Every ton of CO2 is important ”.

Among the consequences Hawkins talks about are an increase in extreme heat, more abundant and unpredictable rainfall similar to those that caused the recent floods in Germany, greater snow loss and melting of permafrost. Under all emission scenarios, the Arctic will be completely ice-free in the summer at least once by 2050, further jeopardizing the survival of polar bears and accelerating warming as less solar energy would be reflected back to. space.

The report focuses more than its predecessors on “unlikely” but potentially disastrous outcomes, which become more and more likely as temperatures rise. “We cannot rule out sudden reactions and critical phases of the climate system, such as a substantial increase in the melting of the Antarctic ice sheet or forest decay,” the authors point out. New research on possible ice sheet collapse under the highest emission scenarios points to an average sea level rise of up to 1.88 meters by 2100, nearly double the previous predictions.

Some changes, such as ocean acidification, will be irreversible for centuries or millennia, regardless of what emissions cuts will be in the coming years. “But the more we limit overheating, the more we can slow these changes in the long term,” says Tamsin Edwards, IPCC author and employee of King’s College London.

“It will be our activities and our choices that will determine what will happen in the coming decades and centuries”, underlines Joeri Rogelj of Imperial College London, one of the authors of the IPCC. Today humanity emits around 40 billion tons of CO2 per year. The scenario with the greatest reduction in emissions expects to bring the quantity to around five billion tons by 2050. An intermediate scenario predicts emissions similar to current levels in 2050. The scenario with the highest emissions foresees a doubling of the levels. According to Rogelj, considering that not all the promises of governments regarding climate action have been translated into political measures, we currently stand between the intermediate scenario and the one with the highest emissions. In this perspective, the temperature increase would be 2.7 and 3.6 degrees respectively.

Changing the course to get closer to the scenario with the lowest emissions – the only one in which overheating could fall back below 1.5 degrees – will be the main objective of the nearly two hundred countries that will meet in Glasgow for the summit in November. on climate Cop26.

According to Piers Foster, a professor at the University of Leeds and one of the authors of the IPCC, the report clearly indicates that zeroing out net emissions can stabilize temperatures. “The good news is that we can be confident that short-term emissions reductions can slow the pace of unprecedented warming.”

The report – Physical science basis summary for policy makers, written by Ipcc Working Group I – reinforces many of the statements proposed in 2013, mainly thanks to the collection of evidence and the combination of models and observations, as well as a better understanding of physical processes.

The IPCC report has an important weight because it is “signed” by 195 governments, whose representatives have signed the document in the last two weeks. Next year, the current report will be followed by two more studies on the impact and solutions to climate change.

(Translation by Andrea Sparacino)