"Boiling" oceans and unprecedented melting accelerate the rise in ocean levels. The global average sea level rise reached a new record in 2023, according to satellite measurements that have been carried out since 1993. According to experts, it is another consequence of the continued warming of the oceans ( and its thermal expansion), as well as the melting of glaciers and ice sheets (Greenland and Antarctica), which are the main factors that explain the elevation.
The rate of sea level rise worldwide has doubled in 20 years. It has gone from a rise of 2.13 millimeters every year between 1993 and 2002 to 4.77 millimeters every year between 2014 and 2023. This is indicated in the 2023 balance sheet by the World Meteorological Organization (WMO ).
The report confirms that 2023 was the warmest year of the 174 years of observations. The global mean near-surface air temperature was 1.45°C above pre-industrial levels (relative to the 1850-1900 average).
The latest climate findings have been overwhelming again. By 2023, more than 90% of ocean waters experienced heat waves at least once, and glaciers under control since 1950 lost the largest amount of ice on record.
This increase in long-term global temperature "is due to the increase in the concentration of greenhouse gases in the atmosphere", says the report. In addition, the conditions imposed by El Niño, another relevant factor in the increase in temperatures, have an impact. El Niño is a cyclical natural warming that begins in the equatorial Pacific with impacts all over the planet and that had a prominent episode last year and a duration that is still being felt.
However, one of the most relevant elements is the accelerated rise of the sea level. In the period from 1993 to 2002, the average level of this rise was 2.13 millimeters each year; the following ten-year period (from 2003 to 2012) rose to 3.33 millimeters each year; and finally, the most recent decade, between 2014 and 2023, amounted to 4.77 millimeters each year.
The rise in sea level is a consequence of the high temperatures of the planet, as well as the heat transmitted to the oceans and the melting of both glaciers and other frozen layers. "Climate change goes far beyond temperatures. What we are witnessing in 2023, especially in terms of ocean warming, retreat of glaciers and unprecedented loss of Antarctic sea ice, is a cause for particular concern", says the Secretary General of the WMO, Celeste Saulo.
The warming translated into high global average sea surface temperatures, which reached record highs starting in April. And the result is that the record highs of July, August and September were beaten by a particularly 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. Widespread marine heat waves in the North Atlantic began during the Northern Hemisphere spring and reached their maximum extent in September. At the end of 2023, marine heat waves were detected throughout the North Atlantic, with temperatures that were 3 °C above average.
Meanwhile, for the twelfth consecutive year, the Mediterranean Sea was almost completely affected by strong and severe marine heat waves.
A second key factor in this rise in the sea was the melting of the two ice sheets that propel this phenomenon: those of Greenland and Antarctica. If you add the two together, the result is that the seven years of greatest ice melt on record have occurred since 2010. Mass loss rates increased from 105 gigatons each year between 1992 and 1996 to 372 gigatons each year between 2016 and 2020. The latter equates to a global sea level rise of approximately 1 mm each year.
In addition, it is joined by the fact that the large glaciers, which are subject to continuous monitoring, suffered during the period of the hydrological year 2022-2023 the greatest loss of ice since there are records (1950- 2023), as a result of an extremely negative mass balance both in western North America and in Europe.
In the European Alps, the melting season of the glaciers 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 experienced an unprecedented loss of ice mass by 2023, at a rate five times higher than that measured during the period 2000-2019. Glaciers in western North America are estimated to have lost 9% of their 2020 volume over the period 2020-2023.
For its part, the extent of the sea ice that surrounds Antarctica was, by far, the lowest it has been on record. The winter's frozen surface shrank by more than 1 million square kilometers from the previous record low, equivalent to the combined size of France and Germany.
The cumulative effects of warming means that the limit increase in temperatures of 1.5º C, set in the Paris Agreement, signed by 195 countries that promised to act against warming, is about to be crossed "We have never been so close - even temporarily, for now - to the lower limit of 1.5 °C of the Paris Agreement on climate change," said Celeste Saulo, secretary general of the agency . "The WMO community sounds the red alert to the world," he added. In 2023, the limit was not exceeded and the rise in temperatures was 1.45º C. However, an unusually hot start to 2024 has meant that the limit has been exceeded, if the average is taken into account of 12 months (from March 2023 to February 2024); in this period an increase of 1.56º C was reached, according to the Copernicus Climate Service of the European Union.
