A warming of + 1.5 ° C in 2030, and beyond? Why "Every Tenth of a Degree Counts"

"Humanity is walking on a thin layer of ice and this ice is melting fast," warned UN Secretary-General Antonio Guterres on Monday (March 20th). And this ice is melting all the faster as global warming accelerates. By the years 2030-2035, it will reach 1.5 ° C compared to the pre-industrial era, confirmed Monday, March 20 the experts of the IPCC in their new synthesis report, the sum of the last nine years of research representing the most up-to-date scientific consensus on climate.

An announcement that appears as yet another bad news for the planet while since COP21 in 2015 in France this threshold of + 1.5 ° C was brandished as a compass of climate policies. "Since the Paris Agreement, the stated objective of States is to keep global warming well below 2 ° C compared to the pre-industrial era and to multiply efforts to limit it to 1.5 ° C," says Wolfgang Cramer, director of research at the CNRS at the Mediterranean Institute of Marine and Continental Ecology. "It gave a clear horizon and target for climate policy."

"And indeed, today, looking at the different possible trajectories and the weak efforts put in place by governments, it seems very difficult to meet this second objective," continues the specialist, who had been one of the main authors of a previous IPCC report published in February 2022.

The numbers speak for themselves. Today, according to the summary published Monday, to have a chance of keeping warming to 1.5°C, greenhouse gas emissions would have to be reduced by about 45% by 2030 compared to today. This would mean experiencing the same decline every year as experienced in 2020, in the midst of the Covid-19 pandemic, when economies around the world were at a standstill.

A colossal drop while the planet seems for the moment to take the opposite trajectory. According to the IPCC, it is heading for a warming of 2.5 ° C at the end of the century if the promises made by the States are respected, 2.8 ° C by following their current policies.

>> Read also: "IPCC report: the key figures of a "bible" of the climate that does not see everything in black"

Global warming, the "fever" of the planet

But for all that, we must not fall into fatalism, experts agree. "Because our current actions will also determine the extent of climate change in the longer term," says Wolfgang Cramer. "The goal, always, is to stay as low as possible."

"This goal, anyway, was already too much... We see it today: we are already at 1.2 ° C of warming and we suffer the consequences with the multiplication of heat waves, droughts, floods ... " he continues.

To understand the importance of these extra fractions of degrees, the specialist draws a parallel with a human suffering from fever. Usually, an individual's body temperature is 37°C. If you add 1°C, he will be in pain and have a slight headache. At 2°C, it will suffer even more. But at 3°C, it can become dangerous, especially if the person is vulnerable.

The same goes for the planet. "The consequences will not be the same at each degree and in different parts of the globe. For the most vulnerable, the consequences will be much greater than for those who are less vulnerable," he said. "1.5°C will always be better than 1.6°C, which will always be better than 1.7°C. Every tenth of a degree counts."

First threat to biodiversity

The illustrations of the consequences of this "fever" of the planet are numerous. Among them: the extinction of biodiversity. The Melomys of Bramble Cay, a small rodent that lived on small islands between Australia and Papua New Guinea has already disappeared because of global warming. "Scientists have shown that its disappearance is due to the submersion of its habitat," Camille Parsesan, director of research at the CNRS and specialist in the links between biodiversity and climate, told France 24 last December. "We also noted the disappearance of 92 species of amphibians, killed because of the proliferation of a fungus. We have proof that it has developed because climate change, by modifying ecosystems, has offered it favourable conditions." Another glaring example is corals. At 1.5°C, 70-90% of them could disappear. At 2°C, the figure rises to 99%.

Today, according to IPBES – the UN's biodiversity experts – more than a million species are threatened with extinction and "climate change is becoming the most important threat to them". "The more it increases, the more ecosystems are disturbed, with consequences for fauna and flora," they note in a report published in 2021.

>> Read also: "Biodiversity, both victim and tool in the fight against global warming"

"More and more intense weather events"

"Each additional degree will also result in more and more intense weather phenomena," Cramer said. "With ever greater impacts for the 3.3 billion people who live in vulnerable areas."

In recent years, some scientists have been working on the "science of attribution", which aims to study the links between extreme weather events and climate change. Through their work, they confirm that heat waves, floods or hurricanes increase in intensity, magnitude or frequency in connection with global warming. They estimate, for example, that this made the heat wave that hit India and Pakistan in March and April 2022 thirty times more likely.

"In the face of these threats, our efforts must also make it possible to slow warming as much as possible," said Gerhard Krinner, a glaciologist and one of the authors of Monday's summary for policymakers. "It's just as important. The faster the warming goes, the less time the population will have to adapt. This will increase the risk of shortages, famines or conflicts."

Not to mention, notes the glaciologist, that some changes will be irreversible and must therefore intervene "as late as possible". "An extinct species, for example, will not be able to reappear," he said. "A melted glacier will have a very difficult time recreating itself. The rise in waters, meanwhile, will continue for centuries more or less quickly depending on warming."

Fear of tipping points

Finally, the two specialists warn against "tipping points". "These events, which it is very difficult to know at what stage of global warming they could occur and which would have major consequences for the planet," insists Wolfgang Cramer.

"This is the case, for example, with the destabilization of the Antarctic ice sheet. The probability of this happening today is low but increases with warming with real risks of a huge acceleration of sea level rise between 1.5°C and 2°C. "Concretely, if Antarctica's frozen ground (permafrost) were to melt, it would release billions of greenhouse gases stored in its ice. This would then warm the planet and further accelerate the melting of the ice – a vicious circle. Other examples often cited include the transformation of the Amazon rainforest into savannah or the melting of the Greenland ice cap.

All these scenarios can be avoided, hammer the two specialists. "Today, we have many solutions in hand, which are available and effective, to slow down and limit climate change. The obstacles are no longer innovation, but political," concludes Wolfgang Cramer. "The efforts we are making now will make all the difference in the long run and can still save us those extra tenths of a degree," Krinner said.

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