When it comes to global warming, some data are more striking than others. Thursday February 8, the European Copernicus Institute indicated that the global temperature was 1.52 ° C higher than the period 1850-1900 between February 2023 and January 2024. Over twelve months, global warming has therefore exceeded the bar + 1.5°C, the most ambitious objective of the Paris agreement, sealed in 2015. This text recommended containing “the rise in the average temperature of the planet well below 2°C (…) by continuing the action taken to limit the rise in temperature to 1.5°C” by the end of the century.
Does the Copernicus communication mean that humanity has already failed to respect the reference text of climate diplomacy? Although this data is alarming, the average warming must be measured over a much longer period to be relevant.
“When climbing a mountain, we pass through intermediate peaks and then go back down. The passage of a summit does not provide information on the average altitude of the hikedeciphers Christophe Cassou, climatologist at the CNRS. Natural climate variability can create temporary rises and falls, but, one thing is certain, human-caused warming has an upward trajectory. » To conclude that the Paris Agreement thresholds have been exceeded, it will take several years of exceeding +1.5°C.
Question of calculation
There remains the methodological question of calculation. The Paris agreement says nothing on this subject. In their sixth assessment report, scientists from the Intergovernmental Panel on Climate Change (IPCC) advised that the bar would be crossed when average warming had exceeded 1.5 degrees for two decades.
This time scale makes it possible to erase certain aspects of natural climate variability, for example interannual phenomena (El Niño, La Niña or the warming of certain parts of the oceans) but also multidecadal events (the deep circulation of ocean masses which can lead to variabilities of plus or minus 0.2 °C).
The year 2023, the hottest year measured since records began, is the consequence of human-caused climate change, but it was also influenced by El Niño from the month of June, “even if it was less strong than those of 1998 and 2016”specifies Mr. Cassou.
“The Paris agreement does not precisely define how we calculate a warming of 1.5°C, but we really need to understand this figure as an objective of stabilizing temperatures in the long termsummarizes Robert Vautard, co-chair of group 1 of the IPCC. And to measure the evolution, we must look at the average over several decades and its trend, erasing the effects of natural variability and noise. This is what scientists do by choosing a period of twenty years. »
You have 50% of this article left to read. The rest is reserved for subscribers.