Harvard scientists find the first definitive proof of the rise of oceans

"There it was — a sea level fingerprint, proof of their existence."
Baba Tamim
A giant piece of Ice breaks off the Perito Moreno Glacier in Patagonia, Argentina
A giant piece of Ice breaks off the Perito Moreno Glacier in Patagonia, Argentina


Harvard scientists have discovered the phenomenon essential to anticipating the effects of climate change.

The study is the first indisputable evidence of sea level fingerprints from glacial ice sheet melting, according to a press release published by Harvard University on Thursday.

"In sea-level physics, almost everyone assumed that the fingerprints existed, but they had never been detected at a comparable level of confidence," said Jerry X. Mitrovica, Harvard geophysicist and the study's lead author.

Sea levels change unexpectedly as a result of glacial ice sheets melting. Despite what logic would predict, the levels in the area actually decrease. But they go up thousands of miles distant in a sort of seesaw effect. The gravitational attraction toward the ice sheet is lost, which causes water to spread away. Sea level fingerprints are the patterns of how that occurs.

"Ocean level projections, urban and coastal planning — all of it — has been built on the idea of fingerprints," said Mitrovica, who is also the Frank B. Baird Jr. Professor of Science in the Department of Earth and Planetary Sciences at the university.

"That's why fingerprints are so important. They allow you to estimate what the geometry of the sea level changes is going to be like … so we now have much more confidence in how sea level changes are going to evolve. … If fingerprint physics wasn't correct, then we'd have to rethink all modern sea level research."

The significant variations in water levels caused by shifting tides, currents, and winds have made it extremely difficult to trace sea level fingerprints. This puts researchers in the difficult position of trying to link millimeter-level water motions to glaciers melting thousands of kilometers distant.

The new study's findings were published on Thursday in Science journal.

30 years of observational data

Harvard scientists find the first definitive proof of the rise of oceans
Observational and topographic features around Greenland. (A) Availability of SSH data from satellite altimetry. (B) Ocean bathymetry based on ETOPO.

In order to identify rising and falling ocean levels from the fingerprint, the new study used recently made public satellite data from a European marine monitoring organization that collected more than 30 years' worth of observations in the vicinity of the Greenland Ice Sheet and much of the nearby ocean.

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Mitrovica and colleague David Sandwell from the Scripps Institution of Oceanography noticed the satellite data. Records from this area had often only gotten as far south as Greenland, but in this latest release, the data reached 10 degrees higher in latitude, giving the scientists the opportunity to spot a potential glimpse of the seesaw generated by the fingerprint.

"I was completely amazed. There it was — a sea level fingerprint, proof of their existence," said Sophie Coulson, Harvard alumna, a postdoctoral fellow at Los Alamos National Laboratory.

"This was a really, really exciting moment for all of us. There are very few moments in science which provide such simple, remarkable clarity on complex Earth processes."

Coulson, also the lead author of the study, was instrumental in confirming the fingerprint signal that sea level scientists had been pursuing for decades.

Coulson, an expert in predicting sea level change and crustal deformation associated with melting ice sheets and glaciers, gathered the most useful data on ice height change within the Greenland Ice Sheet and reconstructions of glacier height change throughout the Canadian Arctic and Iceland.

By combining these several data sets, she made estimates for the area from 1993 to 2019 that she then compared to the fresh satellite data.

A one-to-one match demonstrated with greater than 99.9 percent certainty that the satellite-measured pattern of sea level change is a fingerprint of the melting ice sheet.

The Greenland ice sheet is melting faster

Harvard scientists find the first definitive proof of the rise of oceans
Arctic Iceberg, stock photo.

Vast amounts of frozen water are present in the Greenland ice sheet, which makes up over 80 percent of the island nation.

The new finding supports and gives more confidence to the predicted sea-level changes made by computational models.

They are essential for comprehending the effects of climate change, making it abundantly evident that the Greenland ice sheet is melting faster.

According to a recent study, the Greenland ice sheet's rapid melting is the primary cause of 20 percent of the global sea level increase. Even if humans stopped burning fossil fuels, the world's sea levels would rise by at least 10 inches.

Study abstract:

Rapid melting of ice sheets and glaciers drives a unique geometry, or fingerprint, of sea level change. However, the detection of individual fingerprints has been challenging because of sparse observations at high latitudes and the difficulty of disentangling ocean dynamic variability from the signal. We predict the fingerprint of Greenland Ice Sheet (GrIS) melt using recent ice mass loss estimates from radar altimetry data and model reconstructions of nearby glaciers and compare this prediction to an independent, altimetry-derived sea surface height trend corrected for ocean dynamic variability in the region adjacent to the ice sheet. A statistically significant correlation between the two fields (P < 0.001) provides an unambiguous observational detection of the near-field sea level fingerprint of recent GrIS melting in our warming world.

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