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Houston-based researcher's method to track melting glaciers could change sea level rise forecasting

Houston Chronicle 11/25/2022 Samantha Ketterer, Houston Chronicle

Pietro Milillo spends his days dissecting a map of red, green and blue.

The colorful topography of Antarctica paints a grim picture. Using radar imaging technology, the map allows the University of Houston civil engineer to track the rates that glaciers are retreating – and his findings have a direct bearing on how scientists will understand future sea levels and climate risk.

“We are the first generation that is seeing this kind of effect and the last generation that can do something about it,” Milillo said, paraphrasing a quote from former President Barack Obama. “It’s a really pressing topic, not only for myself but also for our kids and future generations.”

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Milillo now has eyes on up to 50 glaciers, many of them retreating at higher rates than ever recorded. Using a satellite remote imaging system known as synthetic aperture radar interferometry, he regularly measures and records glaciers’ “grounding lines,” or the boundaries underneath them where frozen land meets warmer water.

Scientists around the world are using his data every day to inform their own work in the Antarctic.

“Pietro has sort of become the leading expert on a way of mapping how the ice is changing,” said Ted Scambos, a senior research scientist and glaciologist at the University of Colorado-Boulder. “He’s using radar data to map the line at which the ice sheet begins to float as it flows out to the ocean. That turns out to be a really important line for the stability of the ice sheet.”

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Grounding lines are particularly vulnerable zones that mark where the glacier goes from supported by rock to floating as an ice shelf. As a result of global warming, increasingly warm water infiltrates the bottom of the glacier, the ice melts and the grounding line retreats, thinning the glacier, Milillo said.

Glaciers don’t melt because of the sun – they are constantly moving underneath themselves, and they melt when their speed increases, Milillo said. When grounding lines retreat and the glacier becomes thinner, water flows faster and accelerates melting, he said. Those thinning ice shelves are then responsible for the integrity of the entire structure.

“Grounding lines and ice shelves are the gatekeepers of Antarctica,” he said. “If you don’t have ice shelves, the glaciers will completely flow faster and in this specific area, they will collapse.”

A “fast” glacier recedes at more than 1 kilometer a year, but Milillo’s data has found receding rates of 2.5, 3 or 4 kilometers per year, he found in a study published in February.

Those rates pose the biggest question for climatologists to answer. Milillo’s numbers can be used to calculate expected sea level rise, and he said he hopes his data will decrease the margin of error, or uncertainty, associated with current projections.

At the worst, if all ice above floatation in Antarctica melted, the global sea level would go up by 58 meters, or 190 feet on average – meaning some areas would see higher, Milillo said. That would have dire effects on coastal populations: About 267 million people worldwide live on land less than 2 meters, or 6.6 feet above sea level.

Those projections are scary, Milillo said. But when he looks at his own data, he is only motivated.

“It’s bad news," he said. “But my opinion is, if it’s bad news, it’s better to know than to be ignorant about it.”

“It actually gives me hope, because I’m aware of how fast glaciers are retreating and I’m eager to share this information with the world and the scientific community. If there’s a coworker of mine who for example is a climatologist or is a modeler, I would like for them to have my data to actually come up with some more detailed answers.”

The Italian Space Agency has provided Milillo free access to the satellites he uses for radar data collection. It’s one of many projects he’s involved in: On top of tracking the problem at its source, he is also following where the water flows through a $675,000 grant from NASA. That project assesses flood risks of sandy beaches and dunes, he said.

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