Scientists have thoroughly demonstrated that we are overheating our planet by emitting greenhouse gases, with the vast majority of this (89%) coming from fossil fuels. As this process of climate change worsens, humans will continue to endure extreme weather events including intensified storms, droughts, heatwaves, wildfires and floods.
That last category of natural disaster, floods, deserves particular attention because billions of humans live on or near coasts. Climate change is causing the Arctic and Antarctic alike to slowly melt, contributing to rising sea levels that will subject affected residents to frequent flooding – and, in some cases, entirely submerge their communities under water.
To avoid or at least minimize this to the greatest extent possible, it is critical to understand the rate at which Earth's cryosphere (the Arctic and Antarctic "frozen" areas) is disintegrating. One way of doing so is to look at Earth's history, which is exactly what researchers from the University of Cambridge and the British Antarctic Survey did recently.
As they explain in their recent study for the journal Nature Geoscience, the West Antarctic Ice Sheet — which is roughly the size of Mexico (1.97 million square kilometers in area), and which is already melting at an alarming rate — once underwent a period roughly 8,000 years ago in which it dramatically and quickly shrank.
"We knew that the Antarctic ice sheet was larger at the last glacial maximum (20,000 years ago) than today," Professor Eric Wolff, the Royal Society Professor of Earth Sciences at the University of Cambridge and corresponding author of the study, told Salon by email. "But what we didn't know was when it retreated and how fast it retreated. Our study proves (for sure, I would say) that in this large sector of the continent it occurred at 8,200 years ago, and it was really fast — a 400 meter drop in the ice sheet surface in 200 years."
To learn this, the researchers drilled a 651-meter-long ice core from Skytrain Ice Rise in 2019, which formed as layers of snow falls and turns into ice over thousands of years. As they do so, they trap bubbles of ancient air and contaminants which provide information about Earth's past. They then studied it in detail such as by measuring stable water isotopes (to learn about the temperatures when the snow fell) and the pressure inside air bubbles (which helps determine the elevation at which the snow fell). In a sense, the ice cores serve as a time capsule into Earth's meteorological past, with information that experts can use to project into its future.
Wolff elaborated on the study's implications for humanity. For one thing, it confirms the mechanisms seen in ice sheet models which anticipate very fast retreating; now scientists know that this has already happened at least once. In addition, there were so many models run for both the past and the future that scientists can select the ones where the retreat occurs at the correct time and extrapolate from those about future melting events.
"This is a study that shows how looking at the past can help us understand how the future may pan out," Wolff said. "It looks at a process of a much larger ice sheet retreating to its present size, whereas in the future we worry about the present ice sheet getting much smaller. But this informs us about how the processes work in real life."
If one imagines this resulting in a scenario out of a disaster movie, with giant floods causing apocalyptic conditions overnight, think again. "The rates of change we observed would, if translated to large parts of the ice sheet, imply sea level rises of order one to a few meters per century," Wolff explained. "So that's not by itself causing disasters, but it means that when the next storm surge comes along it's much more likely to overwhelm sea defenses. And its rapid in the sense that raising sea defenses by meters is, for many cities a major engineering issue that may take decades to organize."
The recent study included some standout statistics. Perhaps foremost among them is that in one location, the West Antarctic Ice Sheet managed to shrink by 450 meters over just 200 years. That is larger than the height of the Empire State Building.
Scientists not affiliated with the study supported its conclusions. Dr. Richard B. Alley, a professor of geosciences at Pennsylvania State University, told Salon that the study is "beautiful work," adding that it has "first-rate analyses" and is "comprehensive." Alley pointed out that "one of the difficulties in projecting large future changes in ice sheets and sea level is that we haven’t had instrumental records of large changes in the past for testing the models and gaining knowledge for improving them. We can test against the small changes that have occurred while we’ve been here watching, but how to test against larger changes?"
It is in this field, Alley asserted, that the new study makes its most important contributions, and in the process "provides really strong evidence of past changes in an important part of the ice sheet, involving processes that are likely to be important in the future."
Dr. Eric Rignot from the University of California, Irvine's Department of Earth System Science also told Salon by email as a "very good paper," observing that it "is important to know to establish some boundaries on how fast an ice sheet can melt away in a changing climate. In this study, the authors report 270 km of retreat in 400 years, or 0.7 [kilometers per year], which is within the range of what we observe today in some rapidly changing sectors of Antarctica and Greenland."
Now scientists can help trace how fast a retreat can proceed both in that region of Antarctica and elsewhere with comparable conditions. (While 0.7 kilometers per year is a breakneck pace for this type of ice melt, Rignot added that there are areas in Antarctica where the rate of melt is 1.0 kilometers per year.) "This study among other things shows that we are experiencing very significant changes in Antarctica right now and need to take it seriously," Rignot said.
Dr. Josh K. Willis, a climate scientist at NASA's Jet Propulsion Laboratory with expertise in sea level rise and ice loss, told Salon that "the big thing about this study is that it shows just how fast these gigantic rivers of ice can change. In just 200 years, this glacier had a huge and sudden response as the planet warmed up thousands of years ago. We tend to think of this ice as reacting very slowly. But as paleoclimate scientists bring prehistoric changes into sharper focus, we keep finding out that these giants are more nimble than we thought."
In addition to helping climate scientists better reconstruct the past and predict the future, the study also underscores the importance of proper preparation for climate change. While the sea level rise will not cause floods akin to the Book of Genesis, there are many locations that will still be quite vulnerable to dangerous levels of flooding. If nothing else, the new research makes it clear that the types of scenarios are indeed possible.
"In some places it's a question of raising large scale sea defenses (like the system now protecting Venice)," Wolff told Salon, who noted that his expertise is in assessing how high the sea may rise rather than how to protect against sea level rise. "It may be possible to protect individual buildings and infrastructure against higher tides. But in some cases, communities may have to accept that some locations can't be defended against sea levels that are one to several meters (or 3 to several feet if you readers prefer), and they may need to prefer to relocate some communities. Bangladesh is always given as the prime example of areas where sea level rise of only meters can make large areas uninhabitable, but I think Florida would also be concerned, for example."
