in 30 years +9.1 cm, in 2040 there will be 18. Maldives, Pacific islands (and Venice) at risk -

in 30 years +9.1 cm, in 2040 there will be 18. Maldives, Pacific islands (and Venice) at risk -

Of Paolo Virtuani

Satellite data since 1993. The causes? Melting of ice and thermal expansion of water. The reason? Global warming

Sea level is rising at an alarming rate, indeed the rate of growth is accelerating. According to the study conducted by NASA and the French National Center for Space Studies (CNES), based on data collected over the last 30 years by satellites, since 1993 the water level in the oceans has grown globally by 9.1 centimeters. But, what is even more worrying, the rate of increase is continuously increasing and currently has reached 4.4 mm per year. Alone in 2022, sea levels rose by 2.7 millimeters: equivalent to pouring the contents of 1 million Olympic swimming pools a day for an entire year. If this trend continues, and there is currently no way to reverse it, sea levels will be 18 centimeters higher in 2040 than in 1993.

Between El Nio and La Nia

In 2022, in reality, the increase was lower than the expected annual rate. For Karen St. Germain, director of the NASA Division of Earth Sciences in Washington, it depended on presence of the Nia, the cold phase of the periodic oscillation that originates in the Pacific Ocean, best known for its warm phase known as El Nio (Enso according to the denomination of climatologists). During La Nia, sea levels can even drop as it is a phase that generally causes more rain on land.

The causes

The causes of sea level rise are basically two: ice melt (approximately 65% ​​of the overall increase) and thermal expansion (35%).
1 - with global warming, caused by greenhouse gas emissions due to human activities, continental ice melts and brings more fresh water to the seas (since 2002 Greenland has lost about 280 billion tons of ice a year, Antarctica 150 billion tons/year)
2 - as global temperatures rise, water expands and sea levels rise (partly offset by increased evaporation).

The measurement

Sea level measurement is done today with precise radar altimeters, previously with ocean buoys. Scientists estimate that the level has risen by 21-24 centimeters over the past 140 years. From the first space measurements carried out by the Topex-Poseidon mission, we moved on to the very modern European satellites (with a strong Italian participation) of the Sentinel constellation.

The effects

40% of the world's population lives within 100 kilometers of the coast, equal to 3 billion people, and is directly subject to the effects of rising water levels. Antonio Guterres, UN secretary general, recently reminded the United Nations Security Council that rising levels threaten millions of people who will be left homeless and will be forced to migrate to higher lands. New international laws are needed immediately to protect those who have been left homeless and even stateless. Some countries could cease to exist, engulfed by flood-worthy waves, he added. Some projections for 2100 indicate that 33 Italian coastal sites risk disappearing, including Venice and the Po delta (with the rise of the saline wedge and the pollution of fresh water aquifers for irrigation and food use). In 2017, the sea level on the Dutch coast was 11 centimeters above average.

The island states will disappear

Island states from the Maldives to the Pacific are gravely concerned. In the Maldives they speculate about building a floating city, in many Pacific islands, as in Vanuatu some villages have already been submerged and had to be moved higher up. But many coral islands are flat, as in Kiribati, and emerge no more than a meter from the sea. Where to go? Some are thinking of migrating, but not all states seem willing to welcome refugees from the coming flood.

March 19, 2023 (change March 19, 2023 | 11:47 am)

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