Global sea levels will rise by an average of at least three feet over the next 100-200 years, NASA scientists announced in a media teleconference last week.

The effects from sea level rise may cut global GDP by as much as 9.3 percent annually, according to researchers at the Global Climate Forum. However, while building dikes in coastal areas worldwide could significantly reduce the economic impact of sea level rise, these adaptations could require billions of dollars annually in capital expenditures and maintenance costs to preserve existing real estate, infrastructure, and investments.

Investors will want to understand both the risks and the opportunities.

Newly incorporated data from Operation IceBridge, a six-year NASA mission to survey Earth's polar ice by air, is giving researchers a more detailed picture of the phenomenon than as recently as 2012. The data are consistent with the higher end of previous estimates.

A new visualization of changes in global sea level shows a rise of seven centimeters over the past 22 years, and the oceans continue to advance by more than three millimeters each year.

“Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it’s pretty certain we are locked into at least three feet of sea level rise, and probably more” over the next 100-200 years, said Steve Nerem, lead for NASA's Sea Level Change Team at the University of Colorado at Boulder.


NASA launches new sea level change research initiatives

NASA is intensifying its focus on the issue through a new Sea Level Change Team that will study the specific mechanisms behind the melting. The team will also integrate NASA research results to improve knowledge of the underlying processes and help predict future sea level change. 

NASA also announced the launch of the Ocean Melting Greenland (OMG) mission, a new six-year project to research ice-ocean interactions from the field. While warmer air is melting ice at the surface, coastal areas of Greenland's ice sheet are also being undermined from beneath by warming ocean water.

OMG will improve NASA’s understanding of the pathways by which ocean water seeps into natural troughs between the land and the ice’s underside.

“As sea level gets far enough under [ice sheets and glaciers]…their melting is inevitable,” Dr. David Schimel, Entelligent board member and research scientist at NASA's Jet Propulsion Laboratory, explains.

Predictions may still be too conservative

Much of this now unavoidable rise is fueled by melting ice sheets, particularly in Greenland. Researchers have discovered that “ice sheets are reacting even faster than we had previously suspected,” says Eric Rignot, glaciologist at the University of California, Irvine and NASA’s Jet Propulsion Laboratory. “There’s a large amount of ice there, and the potential for sea level rise is quite great.”

"As the ice melts, water forms on the surface," Schimel explains. Rather than running off into the ocean, it "creates hollows in the ice, and so it takes heat from the surface of the ice all through the ice sheet much more quickly than [expected]."

The process illustrates the complexity of modeling sea level rise. "Nobody had really thought about that phenomenon, and when it was included in models, it greatly increased the rate at which ice could melt," Schimel says.

Still, ice sheets are only one contributor to rising sea levels. Melting glaciers, ice sheets, and thermal expansion (a process in which the volume of water increases as it warms) each contribute a third of the problem, Nerem explains.

Greenland’s Jakobshavn Glacier is of particular concern, says Rignot, who is “in awe of” its pace of retreat. The glacier receded by about a mile in July 2010, and did not re-advance over the winter. Satellite imagery from earlier this month shows that the glacier experienced a massive calving event that created an iceberg nearly five square miles in size. Already the fastest-moving glacier in the world, water now lubricates its underside, increasing its speed to nearly a mile a year.

Calving, or the breakup of ice sheets and glaciers into icebergs, is another accelerating process that’s not well-understood. Conservative models that don’t include icebergs and fast-melt into the ocean “may not be reasonable,” Rignot warns. More reliable predictions will require higher-resolution instruments and more sophisticated models than are currently possible. 

But data collected today may only go so far. There is “no reason to expect the ice sheets will melt in a linear fashion,” Rignot says. “We know from physics that the rate will increase over time,” which is partly why the models are limited, he explains.

"The more the ice melts, the more the remaining ice is exposed to the warming ocean,” creating a snowball effect, Schimel explains. "The coast of Greenland is deeply indented, and [as more of the ice at the coasts melts], more of the glaciers that come down to the ocean will be exposed, [and] the water will be able to get further underneath them."


How sea level rise will affect communities

Changing sea levels may affect millions of people living in coastal areas around the globe, primarily in Asia. Half of the world's population lives within 60 kilometers (just over half a mile) of the sea, and three-quarters of all large cities are located along coastlines, according to the United Nations Environment Programme. This makes communities “tremendously vulnerable to changes in sea level and also, of course, to changes in severe weather that are amplified by rising sea levels," Schimel warns.

As for the United States, NASA’s visualization shows a small but steady rise in sea level on the East coast, and a drop on the West coast. This temporary fall is due to Pacific decadal oscillation, a natural pattern that occurs on top of long-term climate changes. “However, there are signs this pattern is changing,” says Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, California.

"If you have processes in your system that slow down or accelerate warming, you still are accumulating all of the heat,” Schimel explains. Even if “isn’t stored in the ocean this year, it will eventually go back in the ocean."

West coast sea levels will eventually catch up with or even exceed changes on the Atlantic seaboard, according to Willis. “We’ll probably see faster than average sea level rise in the Pacific in the next 20 years,” he warns.

Rising seas are already impacting low-lying areas, and have the potential to measurably change the shapes of their coastlines, scientists say. Miami’s recurrent tidal flooding is one example, according to Michael Freilich, director of NASA’s Earth Science Division. These floods are expected to increase in frequency and severity as sea levels continue to rise.

The newly released data projects impacts over the next 100 years, which can help states and municipalities located in coastal areas plan for the future. Still, the effects of sea level rise are being felt now, says Freilich.

NASA cryosphere program scientist Tom Wagner agrees. “The planet is not just changing - it’s also changed.”



Further reading

Arent, D.J., R.S.J. Tol, E. Faust, J.P. Hella, S. Kumar, K.M. Strzepek, F.L. Toth, and D. Yan, 2014: Key economic sectors and services. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Working Group II Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissell, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 659-708. 

Borisova, Tatiana, N. Breuer, and R. Carricker. 2008 (reviewed December 2014). Economic Impacts of Climate Change on Florida: Estimates from Two Studies.

Heberger, M., H. Cooley, P. Herrera, P.H. Gleick, and E. Moore. 2009. The Impacts of Sea Level Rise on the California Coast. California Climate Change Center.

Tol, Richard S.J., 2011. The Economic Impact of Sea Level Rise. Economic and Social Research Institute, Dublin, Institute for Environmental Studies, Vrije Universiteit, Amsterdam, The Netherlands, Department of Spatial Economics, Vrije Universiteit, Amsterdam, The Netherlands, and Department of Economics, Trinity College, Dublin.$file/EE-0566-112.pdf