the level of the ocean has risen nearly ten centimeters in thirty years

The annual reports of NOAA, the National oceanic and atmospheric administration – the official American agency which studies the ocean and the atmosphere – are always eagerly awaited by the scientific community. Delivered on August 31, the 2021 report shows an absolute record for the concentration of greenhouse gases in the atmosphere: 414.7 ppm (parts per…

The annual reports of NOAA, the National oceanic and atmospheric administration – the official American agency which studies the ocean and the atmosphere – are always eagerly awaited by the scientific community. Delivered on August 31, the 2021 report shows an absolute record for the concentration of greenhouse gases in the atmosphere: 414.7 ppm (parts per million). Unsurprisingly, since without a total cessation of emissions, the stock of carbon continues to accumulate above our heads and to aggravate global warming.

Second lesson, the ocean is rising. Since 1993, the date of the generalization of satellite measurements, it has gained 9.7 centimeters. It’s an average. Depending on the undersea reliefs and currents, the world ocean has hollows and bumps. In some parts of the world, near the poles in particular, coastlines continue to rise slightly, ten thousand years after the end of the last ice age which freed the soil from the enormous weight of the glaciers.

2 – A gradual increase that is accelerating

The rise in the level of the Atlantic on the European coast over the past thirty years is more or less in line with the planetary average, of the order of ten centimeters. It is often higher in Southeast Asia and on the northern coast of Australia. It is lower on the northern Pacific coast of the United States and Canada.

More or less 3.4 millimeters per year, ten centimeters in thirty years, the variation may seem small. Related to longer time scales, it is very significant: more than thirty centimeters in the space of a century, three meters on the scale of a millennium. In truth, the phenomenon is even more worrying for the future of the coasts and their human occupation. Because the increase is not linear. It has crashes – the level has risen in 26 of the last 28 years – and it is going downhill over time. Since 2005, the average would rather be an increase of 3.9 millimeters per year.

3 – Under the pressure of melting ice

Several parameters are involved in the variation of the oceanic level. In the context of global warming, the thermal expansion of water – the warmer water occupies a larger volume – combines with transfers of considerable volumes from the land to the ocean, due to the melting of the ice. on the polar caps of Greenland and Antarctica. On the other hand, the evolution of the pack ice does not ultimately influence the level of the ocean: it is sea water transformed into ice, already present in the ocean.

Leave a Comment