The Antarctic Connection
New research shows that polar ice sheets could become a big contributor to sea level rise
Ice loss proceeds at a staggering rate along the front of Thwaites Glacier (pictured here in 2012), part of the rapidly melting Amundsen Sea sector of Antarctica (map bottom). Ron Anderson (middle) of Oxford, Maryland, has seen the toll of these global changes on the state's coast. Credits: Photo of glacier and map illustration, NASA; photo of Ron Anderson, Daniel Strain
WHEN RON ANDERSON WAS A TEENAGER in the 1970s, he liked to watch the sun set over Benoni Point. The spit of land sat about a mile west of Oxford, Maryland, over the Tred Avon River. Even then, there wasn't much to it. "It was just this little point of land with just these big pine trees and nothing else," says Anderson, who grew up in Easton, not far from Oxford on Maryland's Eastern Shore.
Today, there's almost nothing left of Benoni Point. Over the decades, waves carved away at the land, and rising waters killed off the pine trees, leaving only a small sandy island behind.
Anderson is an aquatic toxicologist at the Wye Research and Education Center, a University of Maryland facility near Queenstown. The 55-year-old now lives in Oxford and is a member of the town's volunteer fire company. Stories like his are common up and down the Eastern Shore.
"Everyone who lives here has seen areas go back to the sea," he says, "or put up bulkheads where they didn't have to 40 years ago."
To be sure, the Bay has eroded land around the Delmarva Peninsula for as long as humans have lived here. But now, sea level rise is speeding up this give and take between land and water. As water levels climb around towns like Oxford, waves reach farther and farther inland, altering the landscape and posing risks to people.
After Tropical Storm Isabel swept through the region in 2003, for instance, the flooding was so bad that Anderson and members of his fire company rode small powerboats down streets to aid stranded residents.
Sea level is rising around the world, a trend scientists have attributed to climate change. Now, new observations are showing that levels on the Mid-Atlantic coast may be climbing at some of the fastest rates seen in the United States. A number of factors are responsible for this rise in water around the Chesapeake Bay. Emerging research suggests that one of the biggest contributors to local sea level rise will come from what may seem an unlikely place: Antarctica.
"There are some pretty stark differences that you see if you compare the sea level rise at a place like Baltimore to, say, Juneau, Alaska," says John Boon, a physical oceanographer and a professor emeritus at the Virginia Institute of Marine Science in Gloucester. The question is, "What's the reason for this?"
The question is an important one on the Bay and along the Mid-Atlantic coastline — an area that many scientists are now referring to as a "hot spot" for sea level rise.
Here, water levels as measured by tide gauges around Baltimore and other towns in the region seem to be climbing twice as fast as the global average increase. And by some estimates, the increase in certain areas is three to four times as fast. For most of the 20th century, that global average was around 1.7 millimeters a year, according to the Intergovernmental Panel on Climate Change, a group that disseminates the findings of climate science research.
Scientists expect that these rates of sea level rise will accelerate in the decades ahead. By 2050, researchers estimate that sea level off the coast of Maryland is likely to rise by a total of around 1.4 feet (0.4 meters). Or by at least 0.9 feet and as much as 2.1 feet. Those are the estimates of a 2013 scientific review led by the University of Maryland Center for Environmental Science.
Oceanographers have identified several factors contributing to this rapid rise in sea level locally. To start off, consider the chemistry of water itself. Because of how water molecules move and interact, warmer water tends to take up more space than colder water. That matters today because most of the earth's oceans are warmer than they used to be, mostly because of manmade climate change.
What is more, in the Chesapeake Bay and Mid-Atlantic regions, not only is the ocean rising, the land is also sinking. It's a natural change that has been going on since the end of the last ice age (see As the Land Sinks).
In the case of these two factors — expanding oceans and sinking land — scientists have a good understanding of how much sea level rise we can expect as the world warms. Less certain is what the contribution will be from a third player: melting ice.
A dangerous mix, sea level rise along the Chesapeake Bay stems from a variety of factors, according to a scientific review led by the University of Maryland Center for Environmental Science (table, above). Together, these factors make the region a "hot spot" for sea level rise and include the impacts of sinking land, melting ice in Antarctica, and changes to the flow of the Gulf Stream. Table source, "Updating Maryland's Sea-Level Rise Projections" report; map, courtesy of Carling Hay and Elsevier
And there is a lot of ice sitting on top of the land masses of Greenland and Antarctica. Scientists refer to these ice sheets, along with other frozen parts of the globe, as the "cryosphere." The physics of how these environments melt are complicated, and scientists are working to better understand how the planet's glaciers are going to behave in a warming world.
It is clear, however, that Greenland and Antarctica are losing ice, and losing it fast, with some glaciers at the water's edge shrinking backward by hundreds or thousands of feet every year. As this ice melts, it adds water to oceans and raises global sea level — like turning on the faucet in your bathtub.
Antarctica is, in many ways, the king of the cryosphere. Greenland is melting at a faster rate, but the southern continent holds a lot more ice, says Christopher Shuman, a geoscientist at the Joint Center for Earth Systems Technology, a collaboration between the University of Maryland Baltimore County and the NASA Goddard Space Flight Center. In total, there's enough ice on Antarctica to raise the world's oceans by more than 200 feet.
"That's what makes it the 800-pound gorilla compared to the more rapidly changing parts of the cryosphere," Shuman says.
It may seem strange that Maryland's coasts could be threatened by a continent thousands of miles away at the earth's South Pole. But when ice sheets melt, sea level doesn't rise evenly across the globe — sea level off Baltimore is rising at a fast clip and it's actually falling near Juneau, Alaska, for instance. Scientists describe the pattern of sea level rise caused by ice loss from a particular ice sheet as a melting "fingerprint."
Gravity is one of the main driving forces behind these fingerprints. "There's a number of things that happen when you melt an ice sheet that have to do with the fact that ice sheets are really big," says Robert Kopp, a climate scientist at Rutgers University in New Jersey.
He explains that ice sheets, especially those sitting on top of Greenland and Antarctica, are so big that they carry their own gravitational pull that draws water toward them. When those ice sheets melt, their gravitational pull weakens, and all the water that had been drawn toward them starts to flow away. The result is that sea level will drop in areas close to the glacier.
"So if you melt Greenland, you cause a sea level fall in Scotland," Kopp says. "If you melt a glacier in Alaska, you cause a sea level fall in Seattle."
But if sea level drops in those locations, then it has to rise somewhere else. Water will tend to build up as far away from the melting ice sheet as possible, Kopp says. That doesn't mean, however, that sea level rise from Antarctica is concentrated around the North Pole. A number of gravitational forces, in fact, add together to put the East Coast of the United States right in the middle of Antarctica's melting fingerprint — in particular, the fingerprint from glaciers on the western, and more rapidly melting, half of the continent called the West Antarctic Ice Sheet.
Because of this fingerprint, melting of ice on Antarctica adds more to sea level near the Chesapeake than melting on Greenland, pound for pound — even though Greenland is a lot closer. For every one millimeter that melting glaciers on the West Antarctic Ice Sheet add to global sea level, waters along the Mid-Atlantic coast rise by around 1.2 millimeters, an increase of 20 percent.
It's a small bump. But over time, it could contribute to the fast rates of sea level rise observed in the Mid-Atlantic. "The United States East Coast is poorly located in terms of ice sheet melting," says Carling Hay, a postdoctoral researcher at Harvard University.
Which makes it all the more worrisome that the 800-pound gorilla that Christopher Shuman describes seems to be waking up. The question is, "What's the reason for this?"
Hanging by its Fingertips
Shuman specializes in studying ice loss on Antarctica. But like Ron Anderson from Oxford, he's seen the evidence of sea level rise closer to home.
The geoscientist grew up in the Philadelphia area and spent family vacations in his grandparents' cabin on the Elk River near Cecilton, Maryland. Today, some of his cousins own the house. Like so many other property owners in Maryland, they've seen the handiwork of rising waters. These days, when a big storm hits the Chesapeake, waves often wash over the family's dock.
"It's a special place to us," Shuman says. "It's also a pretty good vantage point for appreciating the world that's evolving around us."
In recent years, scientists have learned more about the role that Antarctica will play in this evolving world. Their research points to big losses in the years to come.
In one study published in June 2014, for instance, a group of British researchers used satellite data to measure the pace of ice loss across Antarctica. Based on their results, which appeared in the journal Geophysical Research Letters, that loss is proceeding at a gallop. Between 2010 and 2013, the West Antarctic Ice Sheet alone lost close to 150 billion tons of ice each year on average, the team reported. That's enough ice to add nearly four-tenths of a millimeter to global sea level annually.
Even small increases in sea level like these can worsen flooding and the damage it causes in coastal communities, especially during big storms like Isabel, scientists say. "You don't need a very large amount of sea level rise when you couple it to something like a storm surge," says Sridhar Anandakrishnan, who studies glaciers at Pennsylvania State University.
In a second paper published in 2014, a team led by Eric Rignot at the University of California, Irvine, explored the fate of a handful of glaciers on the West Antarctic Ice Sheet — most notably the massive Thwaites Glacier. These chunks of frozen water border the Amundsen Sea Embayment, a large of body of water that has grown increasingly warm over the years.
The glaciers may also be beyond saving. According to the team's analysis, Thwaites and a handful of neighboring ice masses may have melted by so much already that they passed what scientists call a "tipping point" — huge portions of the region could collapse into the sea no matter what happens to the climate. In all, that might be enough melted ice to raise the world's oceans by four feet. That's enough to permanently drown whole segments of the Eastern Shore of Maryland.
The good news for those who live on the Eastern Shore is that because these glaciers are so big, the process will likely take hundreds to more than a thousand years to play out. That's a long time for people, but a blink of an eye in the lifetime of a glacier like Thwaites.
Using satellites, scientists like Christopher Shuman gain a bird’s-eye view of melting ice in Antarctica and Greenland. Here, the NASA scientist stands in front of a visualization of ice loss from the Antarctic Peninsula. Like in other parts of the southern continent, segments of this stretch of ice have been retreating away from the ocean by tens of feet or more every year. Photograph: Michael W. Fincham
The findings by Rignot and his colleagues were also published in Geophysical Research Letters. A second scientific team reached similar conclusions in a study published on the same day in the journal Science.
Despite findings like these, Anandakrishnan says he's an optimist. Even if the loss of the Amundsen Sea Embayment glaciers is unavoidable, other glaciers in Antarctica and elsewhere don't have to endure the same fate. "There are certainly a lot of glaciers that could be saved if you were to take action," he says. Humans can, in other words, slow the melting of the world's ice by combatting climate change, through actions like reducing the use of fossil fuels.
In the end, the loss of glaciers on Antarctica is a global problem. But it's one that can affect life in coastal communities across the planet. Here on the Chesapeake Bay, the way of life in towns like Oxford is tied to what happens to these blocks of ice thousands of miles away. While the science on sea level rise isn't complete yet, it's clear that the general trend presents unpleasant prospects for people who live near the Bay's waters.
Ron Anderson, the toxicologist who lives in Oxford, saw a number of his neighbors lose their homes after Tropical Storm Isabel swept through town. He was in slightly better shape. His house sits about six feet above sea level, which saved it from the bulk of the flooding. Anderson says that he and his wife don't have any plans to move any time soon. But he still worries about what is going to happen in the lifetime of his daughter, who is now in college.
"It might be easier for us to just stipulate in our will that our house be sold versus letting our daughter move in and get flooded in the future," Anderson says. "Because it's a horrible thing. I've seen it happen to many people and I'd hate to see my daughter go through that."