Sea Level Rise Study Shows Land Flowing Along East Coast – Harvard Gazette

In the coming decades, towns and villages along the east coast will have to deal with the impact of sea level rise due to climate change. A new study suggests, however, that sea-level rise could only be part of the picture, as land along the coast is also sinking.

This is the main conclusion of Earth Sciences Professor and Planets Peter Huybers, Science Professor Frank B. Baird Jr. Jerry Mitrovica and Christopher Piecuch, Assistant Scientist at the Woods Hole Oceanographic Institution, who have everything used, from tide gauges to GPS data. brush the most accurate picture of sea level rise on the east coast of the United States. The researchers are co-authors of the study, recently published in Nature.

"What we are seeing on a large scale, and this has come as a surprise to me, is a very clear pattern that one would expect if the reaction to the last ice age was the primary control over the differential rates of elevation of the level. from the sea to eastern United States, "said Huybers. In other words, between 20,000 and 95,000 years ago, the Laurentide Ice Sheet, which covered most of northern North America, was pulling the land up. "Now, thousands of years after the disappearance of the ice," said Huybers, "the mid-Atlantic crust is still weakening.

"In New England, there is not much extra sea level rise due to land movement because it is close to the hinge point," he said. "The ice cap explosion was centered on the central Atlantic and, as it is still stabilizing, the relative rise in sea level in the central Atlantic is about twice the global average. . "

According to Huybers, this means that we must prepare for higher rates of relative sea-level rise along central Atlantic due to the combined effects of the natural subsidence of the land and of the sea. sea ​​level rise caused by man.

"The fact that the middle of the Atlantic sinks due to long-term geological processes means that it will continue for centuries and millennia, in addition to any other change in the level of the sea, "said Huybers. "The central Atlantic is already facing systematic coastal flooding and this problem will only get worse over time."

It is easier to say, however, than to estimate the contribution of various factors to sea-level rise.

"The sea level is a noisy place," said Mitrovica. "The tides go up and down, the waves break, the ice melts, the changes in the ocean circulation, the warming of the ocean. … If you want to understand the sea level in its entirety, you need to know what all these factors are doing. "

One of the first researchers to attempt this feat, he said, was Carling Hay, a former postdoctoral fellow at the Mitrovica laboratory and currently an assistant professor at Boston College.

In 2014, while at Harvard, Hay published an innovative study that used advanced statistical techniques to examine dozens of data sets and factors affecting the elevation of the level of the She came to the surprising conclusion that during the twentieth century sea levels had risen more slowly than expected.

"Unfortunately, this means that if sea level did not rise as fast as we thought in the 20th century, it would increase significantly faster than we had expected for 20 years," Mitrovica said. "It was a real demonstration of the power of statistical work in an area where it was not very common."

With the new study, Mitrovica said, Piecuch took this idea and ran with it. But rather than trying to estimate the sea level rise in the world over the last century, he chose to settle in a given region over a shorter period of time .

"So he can use all kinds of data sets," said Mitrovica. "It can use GPS, which tells you the movement of the earth, but it also has sea level data going back thousands of years, tide gauges and other data. He throws it all in the stew … and asks where the East Coast is going and what is contributing to this change. What Chris has done has solved this long-standing problem that has been going on for 30 years. "

But the work, stressed Mitrovica, is part of a trajectory. "The next thing that will happen is that we will be able to import satellite data and we can step back and look at it globally," he said. "And I think for the first time we may be able to separate the various factors of sea level rise."

"There is a rather confusing set of possibilities for which the sea level could be changed," Huybers added. "What Chris has done is to gather disparate information that has been distributed across multiple sites and at different time intervals and to bring them together in a fully probabilistic manner, thus allowing for better estimates of historical rates of sea-level change. last ice age will contribute to future changes. "

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