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New research confirms that ice sheets in West Antarctica are thinning at a far faster rate than in past millennia. Although scientists are divided as to the cause of the melt, many feel it is directly related to climate change.

The boom must have been deafening last fall as the gigantic chunk of ice finally broke off from the Pine Island Glacier in Antarctica. For almost a year, the creaks and groans from the river of ice had presaged the birth of a new, expansive iceberg. And finally it was there — 34 kilometers long by 20 kilometers wide, an area almost as great as that of New York City.

But as dramatic as the iceberg birth was, it has become a common spectacle in recent years. The gigantic ice shelf that extends into the ocean off of West Antarctica is crumbling — and the glaciers on the continent behind the ice shelf are flowing with increasing speed toward the sea. Concern among scientists is increasing just as quickly. Should the melt-rate continue, or accelerate, many experts fear that the resulting rise in the ocean level could be catastrophic.

Just what is behind the meltdown, however, is not entirely clear. Whereas it is not difficult to pinpoint global warming caused by human activity for increasing temperatures in the Arctic, the southern end of the planet is more difficult. The western side of the continent is thawing out wherever one looks, but on the eastern side, not much is happening.

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By Martin Redfern
Rothera Research Station, Antarctica

UK scientists working in Antarctica have found some of the clearest evidence yet of instabilities in the ice of part of West Antarctica.

If the trend continues, they say, it could lead to a significant rise in global sea level.

The new evidence comes from a group of glaciers covering an area the size of Texas, in a remote and seldom visited part of West Antarctica.

The “rivers of ice” have surged sharply in speed towards the ocean.

David Vaughan, of the British Antarctic Survey, explained: “It has been called the weak underbelly of the West Antarctic Ice Sheet, and the reason for that is that this is the area where the bed beneath the ice sheet dips down steepest towards the interior.

“If there is a feedback mechanism to make the ice sheet unstable, it will be most unstable in this region.”

There is good reason to be concerned.

Satellite measurements have shown that three huge glaciers here have been speeding up for more than a decade.

The biggest of the glaciers, the Pine Island Glacier, is causing the most concern.

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A new NASA study confirms that the surface temperature of Greenland’s massive ice sheet has been rising, stoked by warming air temperatures, and fueling loss of the island’s ice at the surface and throughout the mass beneath.

Greenland’s enormous ice sheet is home to enough ice to raise sea level by about 23 feet if the entire ice sheet were to melt into surrounding waters. Though the loss of the whole ice sheet is unlikely, loss from Greenland’s ice mass has already contributed in part to 20th century sea level rise of about two millimeters per year, and future melt has the potential to impact people and economies across the globe. So NASA scientists used state-of-the-art NASA satellite technologies to explore the behavior of the ice sheet, revealing a relationship between changes at the surface and below.

“The relationship between surface temperature and mass loss lends further credence to earlier work showing rapid response of the ice sheet to surface meltwater,” said Dorothy Hall, a senior researcher in Cryospheric Sciences at NASA’s Goddard Space Flight Center, in Greenbelt, Md., and lead author of the study.

A team led by Hall used temperature data captured each day from 2000 through 2006 from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Terra satellite. They measured changes in the surface temperature to within about one degree of accuracy from about 440 miles away in space. They also measured melt area within each of the six major drainage basins of the ice sheet to see whether melt has become more extensive and longer lasting, and to see how the various parts of the ice sheet are reacting to increasing air temperatures.

The team took their research at the ice sheet’s surface a step further, becoming the first to pair the surface temperature data with satellite gravity data to investigate what internal ice changes occur as the surface melts. Geophysicist and co-author, Scott Luthcke, also of NASA Goddard, developed a mathematical solution, using gravity data from NASA’s Gravity Recovery and Climate Experiment (GRACE) twin satellite system. “This solution has permitted greatly-improved detail in both time and space, allowing measurement of mass change at the low-elevation coastal regions of the ice sheet where most of the melting is occurring,” said Luthcke.

The paired surface temperature and gravity data confirm a strong connection between melting on ice sheet surfaces in areas below 6,500 feet in elevation, and ice loss throughout the ice sheet’s giant mass. The result led Hall’s team to conclude that the start of surface melting triggers mass loss of ice over large areas of the ice sheet.

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The level of the Mediterranean Sea is rising rapidly and could increase by up to half a metre in the next 50 years, scientists in Spain have warned.

A study by the Spanish Oceanographic Institute says levels have been rising since the 1970s with the rate of increase growing in recent years.

It says even a small rise could have serious consequences in coastal areas.

The study noted that the findings were consistent with other investigations into the effects of climate change.

The study, entitled Climate Change in the Spanish Mediterranean, said the sea had risen “between 2.5mm and 10mm (0.1 and 0.4in) per year since the 1990s”.

If the trend continued it would have “very serious consequences” in low-lying coastal areas even in the case of a small rise, and “catastrophic consequences” if a half-metre increase occurred, the study warned.

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Sheets Melting in an Area Once Thought to Be Unaffected by Global Warming

Climatic changes appear to be destabilizing vast ice sheets of western Antarctica that had previously seemed relatively protected from global warming, researchers reported yesterday, raising the prospect of faster sea-level rise than current estimates.

While the overall loss is a tiny fraction of the miles-deep ice that covers much of Antarctica, scientists said the new finding is important because the continent holds about 90 percent of Earth’s ice, and until now, large-scale ice loss there had been limited to the peninsula that juts out toward the tip of South America. In addition, researchers found that the rate of ice loss in the affected areas has accelerated over the past 10 years — as it has on most glaciers and ice sheets around the world.

“Without doubt, Antarctica as a whole is now losing ice yearly, and each year it’s losing more,” said Eric Rignot, lead author of a paper published online in the journal Nature Geoscience.

The Antarctic ice sheet is shrinking despite land temperatures for the continent remaining essentially unchanged, except for the fast-warming peninsula.

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Climate change is having a major impact on Britain’s coast, the seas around the coast, and the life in those seas, a government-sponsored report concludes.

The Marine Climate Change Impacts Partnership (MCCIP) says seas are becoming more violent, causing coastal erosion and a higher risk of flooding.

Higher CO2 levels in the atmosphere are making oceans warmer and more acidic, affecting plankton, fish and birds.

2006 was the second warmest year in coastal waters since records began.

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Here’s a collection of stories about impending sea level rises:

From 27 Jan 06:

Sea level rise ‘is accelerating’

Global sea levels could rise by about 30cm during this century if current trends continue, a study warns.Australian researchers found that sea levels rose by 19.5cm between 1870 and 2004, with accelerated rates in the final 50 years of that period.

The research, published in the journal Geophysical Research Letters, used data from tide gauges around the world.

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From 23 Mar 06:

Sea rise could be ‘catastrophic’

Earth could be headed for catastrophic sea level rise in the next few centuries if greenhouse gases continue to rise at present rates, experts say.

A study in the US journal Science suggests a threshold triggering a rise in sea level of several metres could be reached before the end of the century.

Scientists used an ancient period of warming to predict future changes.

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From 14 Dec 06:

Sea level rise ‘under-estimated’

Current sea level rise projections could be under-estimating the impact of human-induced climate change on the world’s oceans, scientists suggest.

By plotting global mean surface temperatures against sea level rise, the team found that levels could rise by 59% more than current forecasts.

The researchers say the possibility of greater increases needs be taken into account when planning coastal defences.

The findings have been published in the online edition of the journal Science.

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From 17 Dec 07:

Rising seas ‘to beat predictions’

The world’s sea levels could rise twice as high this century as UN climate scientists have previously predicted, according to a study.

The Intergovernmental Panel on Climate Change proposes a maximum sea level rise of 81cm (32in) this century.

But in the journal Nature Geoscience, researchers say the true maximum could be about twice that: 163cm (64in).

They looked at what happened more than 100,000 years ago – the last time Earth was this warm.

The results join other studies showing that current sea level projections may be very conservative.

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