Polar ice melt

Three major glaciers in West Antarctica (Pine Island, Thwaites and Smith) are melting into the Amundsen Sea faster than previously thought.

ESA’s Cryosat polar orbiting spacecraft possesses the capability to observe features in more detail than previous missions and has revealed that the region is now losing more than 150 cubic km of ice into the sea every year.

Cryosat was launched in 2010 with a radar specifically designed to measure the shape of ice surfaces - and its latest results indicate the loss appears to be accelerating

The data, presented at the recent American Geophysical Union (AGU) in San Francisco, show that the loss of ice equates to a 15 percent increase in West Antarctica's contribution to global sea level rise.

Prior to Cryosat, scientists concluded that ice losses from West Antarctica had pushed up global sea levels by some 0.28 mm a year between 2005 and 2010. The new Cryosat data starts from the end of that period.

Scientists say that ice at the Pine Island, Thwaites and Smith glacier ‘grounding lines’ - the places where the ice blocks split from the land and begin to float out over the ocean - is now thinning by between four and eight metres per year.


Three years of CryoSat measurements show that
the West Antarctic Ice Sheet is losing over
150 cubic kilometres of ice each year.

Launched in 2010, CryoSat carries a radar altimeter that can ‘see’ through clouds and in the dark, providing continuous measurements over areas like Antarctica that are prone to bad weather and long periods of darkness.

The radar can measure the surface height variation of ice in high resolution, allowing scientists to calculate its volume accurately.

Prof Andrew Shepherd of Leeds University, who led the West Antarctica study, said that part of the increase of ice loss could be due to faster thinning and part may also be down to CryoSat’s capacity to observe previously unseen terrain.

The mission has also provided three consecutive years of accurate Arctic sea ice thickness measurements, which show that ice covering Earth’s north polar region continues to thin.

Prof Shepherd added: "CryoSat continues to provide clear evidence of diminishing Arctic sea ice.

"From the satellite’s measurements we can see that some parts of the ice pack ice have thinned more rapidly than others, but there has been a decrease in the volume of winter and summer ice over the past three years.

"The volume of the sea ice at the end of last winter was less than 15 000 cubic km, which is lower than any other year going into summer and indicates less winter growth than usual."

Unfrozen planet

Whilst much of the world is in the grip of a financial, economic and industrial crisis, the remorseless growth of the greenhouse gases that cause global warming continues unchecked.

New figures on global carbon dioxide emissions for 2010 from the US Department of Energy make sobering, not to say chilling, reading.

The headline figure is that world carbon dioxide jumped by its largest ever amount in a single year, from 31.6 to 33.5 billion tons. However, close scrutiny of the data from the Oak Ridge National Laboratory reveals other patterns that are just as disturbing.

The key one is the explosive and seemingly unstoppable growth in emissions from China, which leapt by 9.3 per cent over the year to 8.15 billion tons of carbon dioxide. The Chinese are now producing 24.3 per cent of global carbon emissions and have firmly overtaken the US the role of the world's biggest polluter.

Polar scientists also warned this month that Earth's frozen ‘cryosphere’ - from the Arctic Sea in the north to the massive Antarctic ice shelves in the south - is showing unequivocal signs of climate change as global warming accelerates the melting of the planet's coldest regions.

A rapid loss of ice is clear from the records kept by military submarines, from land measurements taken over many decades and by satellite observations from space. It can be seen on the ice sheets of Greenland, the glaciers of mountain ranges from the Andes to the Himalayas, and the vast ice shelves that stretch out into the sea from the Antarctic continent.

The effect of the melting cryosphere will be felt by rapidly rising sea levels that threaten to flood coastal cities and low-lying nations, changes to the circulation of ocean currents such as the Gulf Stream, and possible alterations to the weather patterns that influence more southerly regions of the northern hemisphere.

One of the greatest threats is the melting of the permafrost regions of the northern hemisphere which could release vast quantities of methane gas from frozen deposits stored underground for many thousands of years. Scientists are already seeing an increase in methane concentrations in the atmosphere that could be the result of melting permafrost.

"The melting of the cryosphere is such a clear, visibly graphic signal of climate change. Almost every aspect is changing and, if you take the global average, it is all in one direction," said Prof David Vaughan, a geologist at the British Antarctic Survey based in Cambridge, England.

One of the clearest signals of climate change is the rapid loss of floating sea ice in the Arctic, which has been monitored by satellites since the late 1970s and by nuclear submarines since the beginning of the cold war, according to Prof Peter Wadhams of Cambridge University.

Sea ice is retreating faster and further than at any time on record and this year it probably reached an all-time record minimum in terms of volume and a close second in terms of surface area. On current projections, if the current rate of loss continues, there could be virtually no September sea ice as early as 2015, Prof Wadhams said.

The illustration below, based on NASA satellite data, shows how minimum sea ice extent for 2011, reached on 9 September, declined to a level far smaller than the 30-year average (in yellow) and opened up Northwest Passage shipping lanes (in red).