This is the new "bible" of climate change. The synthesis of the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC) was published on Monday 20 March and is becoming the reference for scientific knowledge on global warming and its consequences.
This document is the result of a compilation of thousands of studies and research in this field conducted since the end of 2014 and the publication of the previous IPCC expert synthesis.
The authors of this "summary for policymakers" note the extent of the damage already caused by these climate changes in a world subject to temperatures that have already increased by 1.1°C compared to the reference period, from 1850 to 1900.
They also highlight the insufficient efforts made by States to meet the commitments made at the various climate summits. The goal of staying within the nails of a temperature rise of between 1.5°C and 2°C by 2100 seems increasingly unattainable. Thus, "the rise in temperatures could exceed 1.5 ° C in ten years if annual CO2 emissions remain at the current level," says Gerhard Krinner, researcher at the Institute of Environmental Geosciences and one of the authors of the IPCC report.
"The benefits far outweigh the costs"
But all is not black in this highly politically sensitive document, every sentence of which has been carefully weighed before publication. "There are multiple options available and effective to reduce greenhouse gas emissions and adapt [the world] to human-caused climate change," says the IPCC in the preamble to this document.
It is, in particular, "the first time that the IPCC has taken a position and considers beneficial in general an effort to keep temperatures below the threshold of a rise of 2 ° C," says Jean-Charles Hourcade, climate economist at the CNRS who participated in the development of the report.
Indeed, until now, these scientists were only assessing how to achieve climate goals and estimating how realistic it was. This time, "they say that the benefits of policies to limit the rise in temperatures far outweigh the costs," says Jean-Charles Hourcade.
A position that clearly aims to push decision-makers to commit more to reforms and investments for a greener future. Even if, in the short term, these changes will cause profound societal upheavals.
The best action program, according to the IPCC, "would be to redirect the bulk of [environmental] investments to developing countries," says Jean-Charles Hourcade. It is in these areas that every dollar invested will have the best return on investment for the planet and the economy.
Key figures of the IPCC report
1.1 °C. Between 2011 and 2020, the global temperature was 1.1°C above that between 1850-1900. It is this latter period that serves as a reference for all the models developed by scientists to calculate our climate trajectory and establish whether, for example, we will be able to contain the rise in temperatures to 1.5°C or 2°C.
3.2 °C. This is the median rise in temperatures predicted by 2100, taking into account all the measures already implemented by States to limit their emissions.
In fact, it should be between 2.2 and 3.5 ° C according to calculations by IPCC scientists. In any case, the efforts made so far are far from sufficient to achieve the objective of a maximum increase of 2°C set in 2015 at COP21 in Paris.
0,45 °C. The IPCC claims that the emission of 1,000 billion tonnes of CO2 due to human activity leads to a rise in global temperatures of 0.45°C each time.
Based on CO2 emissions alone in 2018 – 38 billion tonnes – the temperature rise would exceed 1.5°C within 23 years. But in reality, this threshold is likely to be reached within ten years because of other greenhouse gases such as methane that also contribute to global warming.
3.7 mm. This is the annual rise in sea level due to global warming between 2006 and 2018, notes the IPCC. The speed of this phenomenon has accelerated considerably, since between 1971 and 2006, this annual increase was almost half as fast.
In all, sea levels have already risen by 20 cm since the beginning of the 2006th century. In other words, almost one-fifth of the overall increase occurred between 2018 and 4 (4.<> cm).
6 meters. In the very long term, the sea level could rise by nearly 6 meters, even if humanity manages to keep the temperature rise to 2 ° C at most.
The IPCC report indicates that in this scenario, water levels are expected to rise by 3 to 6 meters over the next 2,000 years. Enough to dramatically change the geography of the globe and make disappear part of the land now emerged.
Even if the temperature rise were limited to 1.5°C, sea levels would still rise sharply – between 2 and 3 metres – in 2,000 years.
Between 3.3 and 3.6 billion people live in contexts that make them highly vulnerable to the effects of global warming. Nearly half of the world's population is therefore likely to be affected by extreme weather events, such as droughts, torrential rains or earthquakes.
It is the populations living in the poorest countries who are most at risk, the IPCC scientists stress again. Between 2010 and 2020, mortality from floods, droughts and hurricanes was 15 times higher in the poorest countries compared to the regions where the so-called rich countries are located.
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