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Multiple heat waves in the Northern Hemisphere and overheating oceans, illustrations of human-induced climate change amplifying natural weather events, could make 2023 the hottest year on record, scientists warn.
Climatologists repeat it: these extreme phenomena are becoming the new norm. And they will get even worse, in duration and intensity, even if humanity drastically reduces its greenhouse gas emissions.
Not just El Niño
The summer of 2022 was the hottest on record even as the Pacific Ocean experienced its third year of the La Niña phenomenon, which is helping to cool global temperatures. The opposite phenomenon, El Niño, has started, world meteorological authorities recently announced, predicting its intensification in the coming months.
“It may have brought some extra warmth to the North Atlantic” which has been evolving since spring at unprecedented temperatures well above all records, “but since El Niño has only just begun, this is probably only a small part of the phenomenon”, writes in a recent bulletin Robert Rohde, from the center Berkeley Earth Research Center.
The group estimates that the year 2023 has an 81% chance of becoming the warmest year on record since accurate records began in the mid-19th century.
June 2023 was the hottest June ever measured, according to the European observatory Copernicus. Over the first six months of the year, 2023 remains in 3rd place, not far behind 2016 and 2020, Copernicus told AFP.
sand and sulfur
The warming of the North Atlantic may also have been accentuated by the reduction of two phenomena that reflect sunlight: sand from the Sahara and sulfur aerosols emitted by cargo ships.
“Exceptionally low levels of dust from the Sahara” have been observed over the ocean “over the past few months”, notes Robert Rohde. A phenomenon attributable to the unusual weakness of the Atlantic trade winds, according to Karsten Haustein, of the German Federal Center for Climatology.
On the other hand, the anti-pollution standards imposed in 2020 on maritime transport have made it possible to reduce its sulfur emissions. For Copernicus, it is also the unprecedented weakness of the Azores anticyclone, synonymous with weak winds and therefore less mixing of surface waters with colder ones at depth, which plays a significant role.
Stationary anticyclones
The warming of the oceans, which absorb 90% of the heat produced by humanity, influences the meteorology of the continents, causing heat waves and droughts in certain places, stormy rains elsewhere. A warmer atmosphere sucks up moisture and dumps it elsewhere, says Richard Allan, a climatologist at the University of Reading.
Scientists also highlight the duration and intensity of anticyclonic systems. Under the effect of these high pressures, “the air plunges towards the ground and heats up, dissipating the clouds, causing intense summer sunshine which dries out the grounds, heating the ground and the air just above”, said Mr. Allan, like in southern Europe right now, because of the hot air from Africa.
“Unknown Territory”
Climate change has made deadly heat waves “more frequent and more intense in most terrestrial regions since the 1950s”, recalled the Intergovernmental Panel on Climate Change (IPCC) in its final summary at the start of 2023.
“We are moving away from the usual natural oscillations of climate into uncharted and more extreme territory”said Melissa Lazenby, a climate change specialist at the University of Sussex.
But humanity has “the possibility of (…) not creating longer and more intense heat waves”, by reducing emissions from the combustion of fossil fuels.
“Just the Beginning”
El Niño could make Earth even hotter in 2024, warns Berkeley Earth.
“This is just the beginning,” says Simon Lewis, a climate change specialist at University College London.
“Sharp, rapid and sustained reductions in carbon emissions, up to full offsetting of residual emissions, can halt warming”recalls the scientist, “but humanity will have to adapt to even more severe heat waves in the future”.