New Research Raises More Questions for Sea Level Rise

April 7, 2023

Meltwater Pulse 1A is scientist’s name for a period during the warmup from the last glacial period (as the Earth’s axis slowly tilted more in the direction of the sun over 10,000 years or so, warming especially the northern polar regions) when a gradual ice retreat turned into a torrent of meltwater, and sea levels rose approximately a meter every 20 years or so, for 400 years.
Since producing the above video, I’ve heard more qualifiers from other scientists. Andrea Dutton PhD cautioned me that, coming out of the ice age, an enormous ice sheet covered what is now Canada, and was exposed to a strong warming – a larger area of ice than we have today.
Eric Rignot has since underlined what he said in the video above, that, even as ice sheets destabilize, strong human action to limit greenhouse warming could slow the process greatly, making it much more likely humans can adapt. 10 meters of Sea Level rise over 800 or a thousand years is one thing. Over 200 years, something else.
Meanwhile, worth remembering that the physics of glacial dynamics are only partially understood, we keep discovering new dynamics of glacial melt, that allow for rapid ice loss not seen in historical human experience.
With that in mind, new research gives us pause.

Inside Climate News:

A new study of the seafloor near the coast of northern Norway brings an ominous warning from the past, showing that some of the planet’s ice sheets retreated in pulses of nearly 2,000 feet per day as the oceans warmed at the end of the last ice age.

The international research team documented that rate of retreat by mapping and measuring what they called “corrugation ridges” spread across about 11,000 square miles of the seabed. The ridges are generally less than 8 feet high and are spaced between about 80 and 1,000 feet apart. They were formed about 20,000 years ago, as the retreating ice sheet moved up and down with tidal rhythms, floating free at high tide and pushing sediments into a ridge at the point where the ice meets the seafloor at every low tide.

The daily tidal cycles produce two ridges per day, enabling the scientists to calculate that the rate of retreat was up to 20 times faster than has previously been measured anywhere else, said co-author Frazer Christie, a polar scientist with the Scott Polar Research Center at the University of Cambridge.

“It’s probably likely, in my opinion, that this rapid buoyancy driven course of retreat could be all that’s needed to set in motion a chain of events that spirals into a more runaway style of retreat,” he said.

Washington Post:

Scientists monitor ice sheet retreat rates to better estimate contributions to global sea level rise. Antarctica and Greenland have lost more than 6.4 trillion tons of ice since the 1990s, boosting global sea levels by at least 0.7 inches (17.8 millimeters). Together, the two ice sheets are responsible for more than one-third of total sea level rise.

The rapid retreat found on the Eurasian Ice Sheet far outpaces the fastest-moving glaciers studied in Antarctica, which have been measured to retreat as quickly as 160 feet per day. Once the ice retreats toward the land, it lifts from its grounding on the seafloor and begins to float, allowing it to flow faster and increase the contribution to sea level rise.

If air and ocean temperatures around Antarctica were to increase as projected and match those at the end of the last ice age, researchers say ice marching backward hundreds of feet in a day could trigger a collapse of modern-day glaciers sooner than previously thought. That could be devastating for global sea levels.

“If temperatures continue to rise, then we might have the ice being melted and thinned from above as well as from below,” said lead author Christine Batchelor, “so that could kind of end up with a scenario that looks more similar to what we had [off] Norway after the last glaciation.”

In the new study, Batchelor and her colleagues analyzed former beds of two major ice streams across the Norwegian continental ice shelf dating back to 15,000 to 19,000 years ago. Using ship-borne imagery, the team calculated the rates of retreat by studying patterns of wavelike ridges along the seafloor. They determined the orderly ridge patterns were probably created as the front of the glacier bounced on the seafloor from daily tides. The team mapped the spacing of the more than 7,000 ridges to calculate the rate of retreat.

“The ice sheet can move over several kilometers per day, touching down at the low tide and the high tide producing these ridges as it does so, kind of bobbing up and down on the tide,” said Batchelor, a physical geographer at Newcastle University.

The team found the retreat rates ranged from 180 to 2,000 feet per day. The extreme rates only lasted on a scale of days to months and probably couldn’t be sustained for much longer. If an ice sheet retreated around 600 meters per day for a year, Batchelor said, you probably wouldn’t have any ice left.

“This is not a model. This is real observation. And it is frankly scary. Even to me,” Eric Rignot, a glaciologist who was not involved in the study, said in an email.

In the past, one of the fastest retreat rates detected for a glacier was at Pope Glacier in West Antarctica, a smaller glacier that’s very close to the enormous Thwaites Glacier, nicknamed the “doomsday glacier” because of its relatively large melting contribution to sea level rise. During a period in 2017, based on satellite calculations, Pope Glacier retreated at a speed of about 105 feet (32 meters) per day. That’s quite fast — but still nothing like the rates of as much as 2,000 feet per day, the study found for the Eurasian ice sheet.


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