Key West Antarctic glaciers already in runaway meltdown

Click to enlarge — Tongue of the Thwaites GlacierNASA/James Yungel

The collapse of glaciers along West Antarctica’s Amundsen Sea would raise seas by 1.2 metres.

Several of Antarctica’s most vulnerable glaciers have already begun a runaway meltdown, two new studies suggest. The work provides some of the first detailed forecasts on how quickly glaciers are likely to disappear from a region that has long concerned scientists.

One modeling paper finds that ongoing losses at the Thwaites Glacier have permanently destabilized that ice river, which drains into West Antarctica’s Amundsen Sea. The second study uses satellite radar observations to reveal that Thwaites and five neighbouring glaciers have nothing to hold them back from catastrophic collapse, leaving them more vulnerable than previously thought.

Were they all to melt, the six Amundsen Sea glaciers studied by Eric Rignot’s team contain enough water to raise global sea level by 1.2 metres. That process is likely to unfold slowly: at Thwaites alone, melting over the next century will probably cause sea levels to rise less than a quarter of a millimeter per year, or just 2.5 centimeters in total.

But that rate could speed up dramatically, to more than a millimeter per year, within two to nine centuries, says Ian Joughin, a glaciologist at the University of Washington in Seattle. “We are seeing the early stages of the collapse,” he says…

Thwaites is important because it flows from a broad, deep interior basin into the sea. Its vast storehouse of ice is big enough to contribute significantly to global sea level rise. The nearby Pine Island Glacier is retreating more quickly than Thwaites but drains only a very narrow trough.

The Joughin study “is a seminal paper,” says Andrew Shepherd, a cryosphere expert at the University of Leeds, UK. “It’s the first to really demonstrate what people have suspected, that Thwaites Glacier is a bigger threat to future sea level than Pine Island.”

Global sea levels are currently rising about 3 millimeters a year. Most of that comes from the thermal expansion of the warming oceans; some also comes from melting ice in Greenland and Antarctica.

“These systems, whether Greenland or Antarctica, are changing on faster time scales than we expected. We are kind of rediscovering that every day,” says Rignot.

It is the nature of scientific research to be conservative. Some may think discussions of events comprised of centuries instead of millennia still to be an exaggerated focus. Why talk about it if you ain’t about to live long enough to see it? That only demonstrates an absence of understanding of science and scientific goals. Everything in science tends to flow from the work that preceded whatever is current.

One important decision that needs to be made is allocation of funds and effort between the northern and southern hemispheres. The former tends to get the most attention because where the bulk of our species live. Sort of a silly reason; but, then, if we are anything it is irrational.

Thanks, Mike

The first map that tracks the motion of Antarctica’s glaciers

Click to enlarge

Scientists have produced what they say is the first complete map of how the ice moves across Antarctica.
Built from images acquired by radar satellites, the visualisation details all the great glaciers and the smaller ice streams that feed them…

It should aid the understanding of how the White Continent might evolve in the warmer world being forecast by climatologists.

This is like seeing a map of all the oceans’ currents for the first time. It’s a game changer for glaciology,” said lead author Dr Eric Rignot. “We are seeing amazing flows from the heart of the continent that had never been described before”…

The map incorporates billions of radar data points collected between 1996 and 2009 by satellites belonging to Europe, Canada and Japan.

Ice drains from the interior via huge glaciers that calve icebergs into the sea…Ice velocities on the new map range from just few cm/year near places where the ice divides into different paths, to km/year on fast-moving glaciers and the ice shelves that float out from the edges of the continent.

RTFA for history and details. Interesting stuff.

Melting ice sheets now largest contributor to a rising sea level

The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new study. The findings of the study – the longest to date of changes in polar ice sheet mass – suggest these ice sheets are overtaking ice loss from Earth’s mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much sooner than model forecasts have predicted…

The nearly 20-year study reveals that in 2006, a year in which comparable results for mass loss in mountain glaciers and ice caps are available from a separate study conducted using other methods, the Greenland and Antarctic ice sheets lost a combined mass of 475 gigatonnes a year on average. That’s enough to raise global sea level by an average of 1.3 millimeters (.05 inches) a year. (A gigatonne is one billion metric tons, or more than 2.2 trillion pounds.) Ice sheets are defined as being larger than 50,000 square kilometers, or 20,000 square miles, and only exist in Greenland and Antarctica while ice caps are areas smaller than 50,000 square km.

The pace at which the polar ice sheets are losing mass was found to be accelerating rapidly. Each year over the course of the study, the two ice sheets lost a combined average of 36.3 gigatonnes more than they did the year before. In comparison, the 2006 study of mountain glaciers and ice caps estimated their loss at 402 gigatonnes a year on average, with a year-over-year acceleration rate three times smaller than that of the ice sheets.

That ice sheets will dominate future sea level rise is not surprising — they hold a lot more ice mass than mountain glaciers,” said lead author Eric Rignot, of NASA’s Jet Propulsion Laboratory, Pasadena, California, and the University of California, Irvine. “What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise.”

Rignot’s team combined nearly two decades (1992-2009) of monthly satellite measurements with advanced regional atmospheric climate model data to examine changes in ice sheet mass and trends in acceleration of ice loss…

The team found that for each year over the 18-year study, the Greenland ice sheet lost mass faster than it did the year before, by an average of 21.9 gigatonnes a year. In Antarctica, the year-over-year speedup in ice mass lost averaged 14.5 gigatonnes…

While this provides one indication of the potential contribution ice sheets could make to sea level in the coming century, the authors caution that considerable uncertainties remain in estimating future ice loss acceleration.

The inherent conservatism of bona fide scientists once again accounts for the element of a “surprising” rate of melting. Not that it means much to pundits or politicians committed to fossil fuel funding. Or, sadly, a populace in general that’s hardly past WW2 in terms of general understanding of science.

The flywheel effect is so strong that even when people are pushed far enough, no longer being able to ignore reality – it will take generations to begin to halt and then reverse the effects of global warming.