The global average rise in sea level in 2023 reached a new record, according to satellite measurements that have been carried out since 1993. For experts, this is one more consequence of the continuous warming of the oceans (and their thermal expansion). , as well as the melting of glaciers and ice sheets (Greenland and Antarctica), which are the main factors that explain this elevation. The rate of sea level rise worldwide over the past ten years (i.e. 2014-2023) is more than double that recorded in the first decade for which data are available (1993). -2002). This is indicated in the report of the World Meteorological Organization (WMO) in its balance for the year 2023.
The WMO report confirms that 2023 was the warmest year of the 174 years of observations. The global average near-surface temperature was 1.45°C above pre-industrial levels (relative to the 1850-1900 average).
This long-term increase in global temperature “is due to increasing concentrations of greenhouse gases in the atmosphere,” the report says.
Additionally, the impact caused by El Niño conditions in mid-2023 contributed to the rapid temperature increase from 2022 to 2023.
But one of the elements that draws the most attention to experts is the behavior of the oceans; and specifically the accelerated rise in sea level.
In the period from 1993 to 2002, the average level of this sea rise on the planet was 2.13 millimeters per year; In the following ten-year period (from 2003 to 2012) it rose to 3.33 millimeters per year; and, finally, in the most recent decade, between 2014 and 2023, it rose 4.77 millimeters per year.
The WMO report highlights that “the rapid rise observed in 2023 is probably due in part to El Niño”, a cyclical warming that begins in the equatorial Pacific with an impact on the entire planet and that had a notable episode last year with a duration that is still felt.
In short, the rate of long-term sea level rise is now more than double what it was at the beginning of what was observed by satellites: it goes from an increase of 2.13 millimeters per year between 1993 and 2002 to 4.77 millimeters per year between 2014 and 2023.
The rise in sea level is a consequence of the planet’s high temperatures, as well as the heat transmitted to the oceans and melting ice, both from glaciers and other frozen layers.
“Climate change goes far beyond temperatures. What we see in 2023, especially in terms of warming oceans, retreating glaciers and unprecedented loss of Antarctic sea ice, is of particular concern,” says the Secretary General of the WMO, Celeste Saulo.
“We have never been so close to the lower limit of 1.5 ° C of the Paris Agreement on climate change, although temporarily for now,” adds Saulo.
The warming also translated into high global average sea surface temperatures, which reached record highs starting in April.
And the result is that the maximum records for the months of July, August and September were beaten by an especially wide margin.
Temperatures were exceptionally high in the eastern North Atlantic, the Gulf of Mexico and the Caribbean, the North Pacific and large areas of the Southern Ocean.
In this sense, the report highlights the strange behavior of some areas of the northeastern Atlantic, which do not correspond to the typical patterns associated with El Niño, whose presence was visible especially in the tropical Pacific.
The heat content in the oceans reached its highest level in 2023, a particularly notable fact in the last two decades.
Almost a third (32%) of the global ocean was affected by a marine heat wave (daily average), surpassing the previous record of 23% in 2016; and all of this caused “damage to vital ecosystems and food systems.”
By the end of 2023, more than 90% of the ocean in non-polar latitudes had experienced heat waves at some point during the year.
Widespread marine heat waves in the North Atlantic, which began during the northern hemisphere spring, reached their maximum extent in September and persisted until the end of the year.
A broad band of marine heatwaves was observed across the North Atlantic in late 2023, with temperatures 3°C above average.
Meanwhile, for the twelfth year in a row, the Mediterranean Sea was almost entirely affected by strong and severe marine heat waves.
Another effect was increased ocean acidification as a result of the absorption of carbon dioxide.
A second key factor in these sea rises was the melting of ice in the two ice sheets that drive this phenomenon: the Greenland ice sheets and the Antarctic ice sheet. If you add the two, the result is that the seven years of greatest melting ever recorded have occurred entirely since 2010.
Mass loss rates increased from 105 gigatonnes per year between 1992 and 1996 to 372 gigatonnes per year between 2016 and 2020. The latter is equivalent to a global sea level rise of approximately 1 mm per year.
The Greenland ice sheet continued to lose mass during the 2022-2023 hydrological year.
It was the warmest summer on record at Greenland’s Summit Station (1.0°C warmer than the previous record).
Added to all this is the fact that the large glaciers, which are the subject of continuous control, suffered in the period of the hydrological year 2022-2023 the greatest loss of ice since there are records (1950-2023), as a consequence of a extremely negative mass balance in both western North America and Europe.
In the European Alps, the glacial melting season was extreme. In Switzerland, glaciers have lost around 10% of their residual volume in the last two years. And, similarly, those in western North America suffered unprecedented glacial mass loss in 2023, at a rate five times higher than those measured during the 2000-2019 period.
Glaciers in western North America are estimated to have lost 9% of their 2020 volume over the period 2020-2023.
Other factors are indicators of warming, although they do not contribute to rising seas. For example, the extent of sea ice surrounding Antarctica was by far the lowest on record. The maximum frozen area reached in winter around this continent shrank by more than 1 million square kilometers compared to the previous minimum record, which is equivalent to the combined size of France and Germany.
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