American and Australian biologists say global warming began earlier than expected. of sponges collected near Puerto Rico, they claim on Monday The nature of climate change The 1.5°C warming threshold has already been crossed, and the 2°C limit will be crossed by the end of the decade.
“The planet's temperature began to rise shortly after the mid-19th century.H “So, we have a few more decades of increase compared to current assessments,” Malcolm McCulloch of the University of Western Australia, one of the authors of the study published on Monday, explained in a press conference last Thursday.
The temperature increase is 1.7°C compared to the pre-industrial average. “We believe the threshold is 2 degrees Celsius [d’augmentation de température par rapport à l’ère préindustrielle] It will be exceeded at the end of 2020, unless there is a significant reduction in emissions. »
The new study is based on a type of Caribbean sponge. ceratoborella nicholsonii, Which grows very slowly and lives at a depth of approximately 100 meters. Over the past 30 years, these sponges, which can live for centuries, have increasingly been proposed as ideal organisms for assessing the planet's past temperature.
The new study shows that the climate emergency is very real, believes Patrick Bonin, head of Greenpeace Canada's Climate and Energy Campaign. “But it is a study of an organism in a specific place on the planet,” Mr. Bonin says.
Study authors in The nature of climate change They believe that the sponges they studied represent the evolution of the planet's average temperature very well, because at this depth, annual climate changes have less impact. The Caribbean is also less affected than the Pacific by El Niño, a weather phenomenon that causes the temperature of the atmosphere and oceans to rise.
Studying these sponges makes it possible to assess the temperature passed with an accuracy of up to a tenth of a degree, Mr. McCulloch said at a press conference. In the data we see a short cooling period associated with some large volcanic eruptions, notably the Tambora eruption of 1815, sometimes called “the year without a summer” because soot from this Indonesian volcano cooled the atmosphere everywhere on the planet for months.
This is partly due to distortion caused by Tambora, and the study's authors believe the current temperature should be compared to the 18th century average.H twentieth century rather than the average period 1850-1900, as the Intergovernmental Panel on Climate Change (IPCC) did. The IPCC uses the 1850-1900 average because it is earlier than the 20thH In the twentieth century, it was difficult to compare thermometer temperature measurements from year to year.
During the press conference, journalists questioned the relevance of discussing the 1.5°C threshold while changing the “pre-industrial” reference period. Currently, the Intergovernmental Panel on Climate Change declares negative impacts associated with exceeding the 1.5°C threshold, but with a reference period of 1850 to 1900. The same negative impacts would be achieved for exceeding the 1.5°C threshold, if we compare the current temperature with that. From the eighteenth centuryH a century ?
“I would say that the serious effects of global warming will happen sooner than expected,” McCulloch said at a news conference. I think we've moved on [les effets négatifs liés au seuil de 1,5 °C] From a decade ago. »
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