New study finds sea level rise accelerating

February 13 2018 - The rate of global sea level rise has been accelerating in recent decades, rather than increasing steadily, according to a new study based on 25 years of NASA and European satellite data.

This acceleration, driven mainly by increased melting in Greenland and Antarctica, has the potential to double the total sea level rise projected by 2100 when compared to projections that assume a constant rate of sea level rise, according to lead author Steve Nerem. Nerem is a professor of Aerospace Engineering Sciences at the University of Colorado Boulder, a fellow at Colorado's Cooperative Institute for Research in Environmental Sciences (CIRES), and a member of NASA's Sea Level Change team.

Global sea level rise is accelerating incrementally over time rather than increasing at a steady rate, as previously thought, according to a new study based on 25 years of NASA and European satellite data.

If the rate of ocean rise continues to change at this pace, sea level will rise 26 inches (65 centimeters) by 2100 — enough to cause significant problems for coastal cities, according to the new assessment by Nerem and colleagues from NASA's Goddard Space Flight Center in Greenbelt, Maryland; CU Boulder; the University of South Florida in Tampa; and Old Dominion University in Norfolk, Virginia. The team, driven to understand and better predict Earth's response to a warming world, published their work Feb. 12 in the journal Proceedings of the National Academy of Sciences.

"This is almost certainly a conservative estimate," Nerem said. "Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that's not likely."

Rising concentrations of greenhouse gases in Earth's atmosphere increase the temperature of air and water, which causes sea level to rise in two ways. First, warmer water expands, and this "thermal expansion" of the ocean has contributed about half of the 2.8 inches (7 centimeters) of global mean sea level rise we've seen over the last 25 years, Nerem said. Second, melting land ice flows into the ocean, also increasing sea level across the globe. Read More

Not if the Seas Rise, but When and How High

Once you’ve read an excellent book about climate change, which Jeff Goodell’s “The Water Will Come” most certainly is, you can never unremember the facts. Elected officials may be busy arguing about whether global warming is real. But most scientists are having other arguments entirely — about whether danger is imminent or a few decades off; about whether our prospects are dire or merely grim.
“Sea-level rise is one of the central facts of our time, as real as gravity,” Goodell writes. “It will reshape our world in ways most of us can only dimly imagine.”
Goodell has little trouble imagining it. He opens “The Water Will Come” with a fictional hurricane whipping through Miami in 2037. It sweeps the Art Deco buildings of South Beach off their foundations, disgorges millions of gallons of raw sewage into Biscayne Bay and eats the last of the city’s beaches. Thousands scramble for bottled water dropped by the National Guard. Zika and dengue fever start to bloom (so much moisture, so many mosquitoes). Out rush the retirees and glamour pusses; in rush the lawyers and slumlords. Within decades, the place is swallowed whole by the ocean. What was once a vibrant city is now a scuba-diving destination for intrepid historians and disaster tourists.
The whole scenario seems indecently feasible by the book’s end.
After this year’s calamitous flooding in Houston and the Caribbean, “The Water Will Come” is depressingly well-timed, though I’m guessing all good books about this subject will be from now on. Political time now lags behind geological time: If we don’t take dramatic steps to prepare for the rising seas, hundreds of millions could be displaced from their homes by the end of the century, and the infrastructure fringing the coast, valued in the trillions of dollars, could be lost.
Unfortunately, human beings are uniquely ill-suited to prepare for disasters they cannot sense or see. “We have evolved to defend ourselves from a guy with a knife or an animal with big teeth,” Goodell writes, “but we are not wired to make decisions about barely perceptible threats that gradually accelerate over time.”
So we stick our heads in the sand. Until the sand disappears, anyway.
https://goo.gl/8wuqjb

Climate change is altering Greenland ice sheet, accelerating sea level rise

The Greenland ice sheet has traditionally been pictured as a bit of a sponge for glacier meltwater, but new research has found it is rapidly losing the ability to buffer its contribution to rising sea levels, says a York University researcher.

York U Professor William Colgan, a co-author on the study published in the journal Nature Climate Change, helped analyse data from three expeditions to the Greenland ice sheet in 2012, 2013 and 2015. The research was done in conjunction with lead researcher Horst Machguth of the Geological Survey of Denmark and Greenland, Mike MacFerrin of the University of Colorado at Boulder and Dirk van As of the Geological Survey of Denmark and Greenland Copenhagen, Denmark.

Colgan spent five weeks with the team in 2013 drilling firn cores in the interior of the Greenland ice sheet. Firn is multi-year compacted snow that is not as dense as glacier ice. Instead, it forms a porous near-surface layer over the ice sheet. Dropped off by a ski-equipped US Air National Guard C-130 Hercules in minus 40 degrees Celsius weather, with 6,000 kilos of supplies and equipment, the team set up several camps and drilled a series of shallow firn cores about 20 metres deep during their time on the ice sheet.

"We were interested in the thin porous near-surface firn layer, and how its physical structure is changing rapidly with climate change," said Colgan of the Lassonde School of Engineering. "The study looked at very recent climate change on the ice sheet, how the last couple of years of melt have really altered the structure of the ice sheet firn and made it behave differently to future melt."

The researchers also towed a radar unit behind their skidoos to gather profiles between core sites along a 100-kilometre path from the low elevation ice sheet margin into the high elevation ice sheet interior. They analysed the firn cores on the spot by cutting them into small sections to quantify their properties, such as their density, so they could compare them with samples collected the following year. "The year-on-year firn changes were quite dramatic," said Colgan.

The team was surprised by what they found. An extreme melt that occurred in 2012 caused a layer of solid ice, several metres thick, to form on top of the porous firn in the low elevation areas of the ice sheet. "In subsequent years, meltwater couldn't penetrate vertically through the solid ice layer, and instead drained along the ice sheet surface toward the ocean," said Colgan. "It overturned the idea that firn can behave as a nearly bottomless sponge to absorb meltwater. Instead, we found that the meltwater storage capacity of the firn could be capped off relatively quickly."

As Machguth said, "Basically our research shows that the firn reacts fast to a changing climate. Its ability to limit mass loss of the ice sheet by retaining meltwater could be smaller than previously assumed."

Because the models scientists use to project Greenland's sea level rise contribution do not presently take firn cap-off into consideration, it means that Greenland's projected sea level rise due to meltwater runoff is likely higher than previously predicted. Getting this newly observed physical process into these models is an important next step for the team.

Using unmanned aerial vehicles, Colgan also plans to begin surveying the changes in ice sheet surface reflectance caused by the development of massive ice layers associated with firn cap-off. There are preliminary indications that firn cap-off is also occurring in the ice caps of the Canadian High Arctic. More

 

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