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Almost every day, peer-reviewed studies of global warming warn that deadly impacts will come sooner and harder than expected.
Virtually none, however, suggests that past predictions of future heat waves, droughts, storms, floods or rising seas have been exaggerated.
So while the nations of the world are piling up in South Korea to validate the first major assessment of climate science conducted by the UN in five years, one wonders: have we underestimated the threat of global warming?
The report of the Intergovernmental Panel on Climate Change (IPCC) on capping the increase in temperature of the Earth's surface to 1.5 ° Celsius (2.7 ° C) F) in relation to pre-industrial levels has not been finalized, delegates planning a five-day meeting – scheduled for Friday – will go overtime overtime.
However, a new 28-page executive summary project aimed at policy makers, obtained by AFP, alarmingly shows that the two-degree ceiling long considered the safety barrier for a climate-friendly world n & # 39; 39 is more viable.
With a warming of only one degree Celsius until now, the planet is in shock from a crescendo of extreme, lethal and costly weather events, aggravated by climate change.
"What scientists plan to do in the future is happening now," Jennifer Morgan, executive director of Greenpeace International, told AFP.
"We thought we had more time, but we do not have any."
The historic Paris Agreement of 2015 encourages its nearly 200 signatories to keep warming to "well below" 2 ° C – and to 1.5 degrees if possible, an ambitious goal that has resulted in the IPCC report.
– & # 39; Short-termism & # 39; –
Many scientists point out that the warnings of a climate-marked future go back several decades.
The 1972 United Nations Conference on the Human Environment, for example, foresaw the possibility of "global and catastrophic effects" of a temperature surge caused by carbon dioxide emissions.
"Many scientists have long known that human-induced climate change could have disastrous consequences," said Jean-Pascal van Ypersele, professor of climatology at the Catholic University of Louvain and former vice president. IPCC.
"Those who have underestimated the severity of climate change are primarily decision makers."
Van Ypersele denounced political inaction to "short-termism" – electoral cycles outweighing long-term issues – and deliberate campaigns by the fossil fuel industry to sow doubt on the validity of climatology.
But Wolfgang Cramer, director of research at the Mediterranean Institute for Biodiversity and Ecology and lead author of the IPCC report, was not in agreement.
"Scientists should be a little more self-critical," he told AFP in Incheon. "Over the past 15 to 20 years, we have focused primarily on the impacts of a world at 2.5 ° C, 3 ° C and even 4 ° C."
"So when the leaders asked," If we shoot at 1.5 ° C, what will it take? "We could only answer:" We do not really know. "
– Inadequate models –
Indeed, the vast majority of the approximately 200 climate models used to generate the IPCC projections in its last major report, published in 2013, assumed a 2C benchmark. Only a handful even considered a world at 1.5 ° C.
And for good reason: although vaguely attached to science, Goal 2C mainly emerged from the political turmoil of the Copenhagen Summit in 2009 and defined the research agenda for almost 10 years.
These previous models were inadequate, said Michael Mann, director of the Earth System Science Center at Pennsylvania State University.
"Too conservative, they have failed to capture all the effects of global warming on extreme weather events such as those that occurred in North America, Europe, and Asia this summer," she said. he told AFP.
The models also underestimated the loss of sea ice in the Arctic, as well as the rate at which the ice sheets located at the top of Greenland and West Antarctic – with enough of frozen water to add 13 meters to sea level – disintegrate.
These "feedback effects", both cause and effect of global warming, are particularly difficult to grasp for the models, noted Mann.
Finally, science is intrinsically conservative, which is even more true for the IPCC, whose credibility – constantly undermined – depends on the fact that it never exaggerates the threat.
"There is a cultural tradition in science, especially climatology, not to want to be alarmist," said Peter Frumhoff, director of science and policy of the Union of Concerned Scientists, a research and development group. advocacy based in Washington.
The 2013 IPCC report, for example, chose not to include in its sea level projection the contribution of the melting ice sheets, which have since become the main factor.
"It was a mistake of lesser drama," Frumhoff told AFP.
