Climate: decades before temperatures drop

Even if the world drastically reduces greenhouse gas emissions, the impact on global warming may not be visible until the middle of the century, according to researchers who fear a boomerang reaction to measures which appear to be wrongly ineffective.

Due to human activities, the planet has already gained at least +1 ° C since the pre-industrial era, increasing climatic disasters.

To combat this climate change destined to worsen with each additional half-degree, the signatories of the Paris Agreement of 2015 have undertaken to reduce their emissions to limit warming to +2 ° C, or even +1.5 ° C.

For the moment, these commitments from the States are not fulfilled. Even if they were, “these efforts could be visible by the middle of the century, but probably not before,” write the authors of the study published Tuesday in Nature Communications.

“Reducing emissions, which is necessary, is effective from the first day, but it will take time before we can measure this effect with certainty,” said Bjorn Samset of the Norwegian climate research center Cicero in a statement.

The climate system is in fact naturally characterized in particular by a significant force of inertia and a high variability from one year to the next.

“Man-made climate change can be compared to a container ship launched at full speed amidst big waves. If you want to slow the ship down, you can shift into reverse, but it will take a while before you can see that it has slowed down, “said the climatologist.

Thus, a significant drop in emissions can be seen immediately on the concentrations of CO2 in the atmosphere, but not on the rise in temperatures which is however responsible for the multiplication of extreme weather events.

Even in the most optimistic scenarios, the first signs of an impact on global warming may be invisible until at least 2035, according to the researchers.

So be patient !, they plead, fearing that this delay could cause a boomerang effect.

This reality “must be clearly explained to policy makers and the public if we are to avoid a negative backlash against policies to reduce emissions that would be perceived as ineffective,” the study insists.

“This does not mean that the decrease (in emissions) has no effect. It just means that we have to be patient, ”insists Bjorn Samset.

“We have piled up problems for our future. But that’s not a reason not to limit the damage now, “said Grant Allen, a researcher at the University of Manchester who was not involved in the study. Even if at the same time, we will have to adapt to the consequences already programmed, he notes.

Several other scientists welcomed the new study, but Piers Forster, a climatologist at the University of Leeds, disputed its findings, calling it “a bleak and useless view of our influence on the climate in the decades to come.”

“According to our own work, society can have a noticeable impact of a drop in the temperature of the planet in the next 15 to 20 years thanks to significant efforts to reduce emissions,” he insisted.

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