Sea Levels Rose 59 Feet When Ancient Ice Sheets Melted: Study

New evidence of ice sheet melting at the end of the last Ice Age clears up previous uncertainties and offers a terrifying glimpse of the future of our oceans.

An isolation lake in northwest Scotland. Sediment analyzed from the bottom of this low-lying lake tells us that it was once connected to the ocean. (Ian Shennan, Department of Geography, Durham University)

(CN) — Scientists have turned to past occurrences of sea-level rise in order to gauge the danger currently facing society today as a result of climate change, finding that significant ice loss at the end of the last Ice Age caused oceans to rise 12 feet every century for 500 years.

In the study, published Thursday in the journal Nature Communications, researchers from Durham University outlined the dangers of rising sea levels and what people should expect if things continue down the current path.

Earth’s oceans have been in failing health for years as a result of human activity, from warming temperatures to acidification to pollution. Rising sea levels — a dangerous side effect of this decline — occurs due to thermal expansion and the melting of ice in normally frozen regions.

Glaciers and ice sheets hold most of Earth’s freshwater, which under healthy conditions remains frozen in regions such as Antarctica and Greenland. According to current estimates, Antarctica is home to about 90% of land-based ice. But as global temperatures rise from atmospheric pollution, this ice is melting at an alarming rate that only seems to be progressing faster the longer it goes unimpeded.

Perhaps the greatest instance of substantial ice loss occurred at the end of the most recent Ice Age over 14,600 years ago. After 500 years, the melting ice sheets caused Earth’s oceans to rise a staggering 59 feet — 10 times the rate currently being seen.

For years, scientists have debated which of the ice sheets of the time contributed most to the spike in sea level. Many fingers point to the Antarctic Ice Sheet, while others point to the ice sheets of the Northern Hemisphere.

“Despite being identified over 30 years ago, it has been surprisingly challenging to determine which ice sheet was the major contributor to this dramatic rise in sea levels,” lead author Yucheng Lin, from the Department of Geography at Durham University, said in a statement accompanying the study. “Previously, scientists tried to work out the source of the sea-level rise based on sea-level data from the tropics, but the majority of those studies disagreed with geological records of ice sheet change.”

Lin added: “Our study includes novel information from lakes around the coast of Scotland that were isolated from the ocean due to land uplift following the retreat of the British Ice Sheet, allowing us to confidently identify the meltwater sources.”

In their study, the team of scientists present new data using the latest modeling techniques to demonstrate the rate of meltwater at the time according to geological sea-level data. Their findings showed that contrary to popular belief, very little of the meltwater originated from the Antarctic Ice Sheet: most actually came from North American and Eurasian ice sheets.

“The technique we have used allows us to really dig into the error bars on the data and explore which ice-melt scenarios were most likely,” said co-author Pippa Whitehouse from Durham University in the statement. “We found that most of the rapid sea-level rise was due to ice sheet melt across North America and Scandinavia, with a surprisingly small contribution from Antarctica.”

The authors note melting of this scale would have been equal to an ice sheet twice the size of Greenland disappearing into the ocean over the span of 500 years. This massive release of water resulted in major flooding in coastal areas and a significant interruption of existing ocean circulation. The good news is that with that debate settled and scientists finally clear on the origins of the meltwater, they can make more precise climate models moving forward. 

This research provides important contributions to the field of climate study as it pertains to observing ocean health and managing sea levels. Understanding the current state of ice sheets and predicting changes will be key in protecting areas and populations prone to flooding and storm damage. 

The researchers add their findings can’t come too soon considering the current state of Greenland’s ice sheets. According to recent predictions, this ice sheet is expected to see unprecedented melting in the near future which will have major consequences for global sea levels. The entire ice sheet has the potential to raise sea levels by approximately 23.6 feet.

“The next big question is to work out what triggered the ice melt, and what impact the massive influx of meltwater had on ocean currents in the North Atlantic. This is very much on our minds today — any disruption to the Gulf Stream, for example due to melting of the Greenland Ice Sheet, will have significant consequences for the U.K. climate,” Whitehouse said.

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