global warming

+7°C: New scientific projections are alarming

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Global warming is shaping up to be more serious than expected, with the worst-case scenario predicting +7°C in 2100, French scientists warned Tuesday, presenting new and very alarming climate models that will serve as a basis for the IPCC.

In 2021, UN climate experts will unveil their new assessment report on climate change, the sixth since 1990. Around 100 French researchers and engineers, notably from the French National Centre for Scientific Research (CNRS), the French Atomic Energy Commission (CEA) and Météo-France, have worked to develop two climate models that will feed into this work.

According to the newspaper The WorldThis colossal task involved some 100 researchers and engineers who simulated more than 80,000 years of climate change, using supercomputers day and night for a year, requiring 500 million hours of computing time and generating 20 petabytes (20 million billion bytes) of data. These models were then subjected to several socio-economic scenarios.

In the most pessimistic scenario, based on rapid economic growth fuelled by fossil fuels, the rise in global average temperature reaches 6.5 to 7°C in 2100. In the latest IPCC report of 2014, the worst-case scenario predicted +4.8°C compared to the pre-industrial period.

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Global average temperature change under different scenarios. CNRS

What would this mean concretely for human societies? In France, the multiplication of heat waves is a good example, the scientists replied at a press conference. The 2003 heat wave, which killed 15,000 people in France and more than 70,000 in Europe, would become the norm by the 2050s.

This would be accompanied by "much longer and more extensive droughts", "from 2070 onwards, a Garonne will be dry for a few months", "agricultural practices that have been heavily questioned", "forest fires that are multiplying in regions where they are not too frequent today", listed David Salas y Mélia, a climatologist researcher and climate manager at the CNRM research centre (Météo-France-CNRS).

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Scientists have also subjected their climate models to alternative scenarios. The most optimistic one, based on strong international cooperation and the priority given to sustainable development, would "just" allow us to stay below the 2°C warming target and "at the cost of temporarily exceeding the 2°C target during the century". This scenario implies an immediate decrease in CO2 emissions, global carbon neutrality by 2060 and a capture of atmospheric CO2 in the order of 10 to 15 billion tonnes per year by 2100, which is technically uncertain.

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The 2015 Paris Climate Accord calls for limiting global warming to well below 2°C or even 1.5°C. The world is not moving in this direction, since the commitments made by States to date would lead to a warming of 3°C. UN Secretary-General Antonio Guterres called a summit in New York on Monday to call on world leaders to raise their ambitions.

The average global temperature at the end of the century is highly dependent on the climate policies that will be implemented now and throughout the 21st century. "CNRS, Météo-France and CEA insist in their presentation.

This news is all the more worrying since these new climate models developed by the CNRM and the Parisian Institute Simon Laplace are more reliable and more refined than the previous ones. « There is a qualitative leap in model results ", insisted Pascale Braconnot, climate modeling specialist at the Laboratoire des sciences du climat et de l'environnement. Other foreign models that have already been made public, and which will also be used by the IPCC, also point towards a more pronounced warming. « This could be explained by a stronger response of the climate to anthropogenic greenhouse gas increases than in the 2012 simulations, but the reasons for this increased sensitivity and the degree of confidence to be placed in it remain to be assessed. ", according to the presentation.

Thanks to this finer scale, researchers have better modelled the consequences of global warming in Western Europe for heat waves, but also on the evolution of the Arctic ice pack, which could disappear or almost disappear in summer by the end of the century.

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