Several articles on climate change and its impact on sea acidity, Antarctica, glaciers
Date added: March 1, 2012
Several recent stories about climate change reveal that the rate of ocean acidification is speeding up, due to increased CO2 in the atmosphere creating carbonic acid in oceans, making their pH lower. The pH is currently dropping by about 0.1 per century. This ocean acidification harms organisms such as corals that rely on dissolved carbonate to make their shells. NASA has observed a massive new crack in the Antarctic ice shelf, which will eventually produce a vast 900 square metre iceburg, though it may not be calved off this year. Attempts to determine whether the Antarctic is losing ice have produced some conflicting data, but recent reports agree that the ice sheet is losing ice – and indeed that the rate of loss has been speeding up. The ice loss is largely in the Western Antarctica, particularly around the Antarctic Peninsula.
Billions of tons of water lost from world’s glaciers, satellite reveals
by Steve Connor
The total volume of water that has melted from all of the world’s polar ice sheets, ice caps and mountain glaciers over the past decade would repeatedly fill Britain’s largest lake, Windemere, more than 13,000 times, according to one of the most comprehensive studies of the Earth’s frozen “cryosphere”.
Using a unique pair of satellites that have monitored the disappearing ice over the entire surface of the globe, scientists estimated that some 1,000 cubic miles of ice has disappeared between 2003 and 2010 – enough to cover the US in one-and-a-half feet of water.
The survey found that the melting of the cryosphere has been responsible for raising sea levels by about half an inch over the same period, equivalent to a rise of about 1.5mm a year. This was on top of sea-level increases due to the thermal expansion of seawater caused by rising ocean temperatures.
Data gathered by the Gravity Recovery and Climate Experiment (GRACE), a joint satellite project run by Nasa and the German government, also found that the amount of ice melting from the mountain glaciers and ice caps that were not in Greenland or Antarctica was actually significantly smaller than previous estimates had suggested.
Instead of contributing nearly 1mm of sea level rise per year as previously suggested, some of the Earth’s glaciers and ice caps, especially in the Himalayas and other mountain ranges in Asia, were melting significantly slower than expected, contributing about 0.4mm of sea level rise per year – less than half the amount predicted.
One explanation for the previous overestimates could be that most of the glaciers that have been studied intensively are at lower altitudes and therefore more prone to melting. Higher glaciers are colder and less susceptible and yet only 120 glaciers out of 160,000 glaciers and ice caps have been directly measured from the ground.
The GRACE satellite experiment, however, covered the entire globe and found that all the world’s glaciers and ice caps combined, apart for those in Greenland and Antarctica, had lost about 148 billion tonnes of ice, or about 39 cubic miles, annually between 2003 and 2010. The individual glaciers on the fringes of Greenland and Antarctic contributed an additional 80 billion tons over the same period, the study published in Nature found.
“This is the first time anyone has looked at all of the mass loss from all of the Earth’s glaciers and ice caps with GRACE,” said John Wahr, professor of physics at the University of Colorado at Boulder, who was part of the research team that analysed the satellite data.
“The Earth is losing an incredible amount of ice to the oceans annually, and these new results will help us to answer important questions in terms of both sea-level rise and how the planet’s cold regions are responding to global change.”
Professor Jonathan Bamber, of Bristol University, said: “Melting glaciers are an iconic symbol of climate change… they seem to have been receding, largely uninterrupted, almost everywhere around the world for several decades.”
1,000 Cubic miles of ice has disappeared between 2003 and 2010 from polar caps.
Gigantic Antarctic crack mapped for the first time
March 1, 2012 (Canberra Times)
NASA’s Operation IceBridge discovers a major rift in western Antarctica, which could produce an iceberg more than 800 square kilometers in size.
In a scene straight out of a science-fiction disaster movie, space agency NASA has revealed what a vast crack across Antarctica looks like up close.
The 2004 disaster movie The Day After Tomorrow opened with a the Antarctic iceshelf cracking before extreme global weather, and now NASA has it live and on YouTube.
In October 2011, researchers flying in NASA’s Operation IceBridge campaign made the first detailed, airborne measurements of a major iceberg calving event while it was in progress.
A section of the massive crack in an Antarctic glacier – which measures 250m at its widest point – that has been mapped by NASA.
By February, IceBridge’s team had mapped the crack in Antarctica’s Pine Island Glacier in a way that allowed glaciologists to fly through the icy canyon.
The animation was created by draping aerial photographs from the Digital Mapping System – a still camera with very precise geolocation ability – over data from the Airborne Topographic Mapper, a scanning laser altimeter that measures changes in the surface elevation of the ice.
Both instruments were flown on NASA’s DC-8 research aircraft and the data was collected on October 26 last year.
The crack formed in the ice shelf that extended from one of West Antarctica’s fastest-moving glaciers.
The path of the crack in the animation stretched roughly 30 kilometres in length (the actual crack was much longer), with an average width of about 80 metres. It was 250 metres at its widest.
The canyon ranged from 50 to 60 metres deep, with the floor being roughly at the water line of the Amundsen Sea.
Radar measurements suggested the ice shelf was about half a kilometre thick, with only a third of it above water.
NASA said scientists had been waiting for the crack to propagate through the rest of the ice shelf and release an iceberg, which they estimated could span 900 square kilometres.
If it did not split off soon, however, the sea ice that formed with the onset of southern winter might keep the ice chunk trapped against the coast for a while.
Almost 70% of the globe’s fresh water is stored as ice in Antarctica, mostly in the huge ice sheet covering the continent. As well as this land-based ice, the sea ice that encircles the continent grows to a wide expanse in winter and almost entirely melts away during the summer.
Scientists trying to resolve these two trends have suggested that the sea ice growth could be happening because the ozone hole over Antarctica is affecting weather patterns in the region. They think changes in weather may be enhancing offshore winds, which spread the sea ice out by pushing it away from the continent. Another theory is that the amount of freshwater in the Southern Ocean has increased, diluting the salt content of the seawater, altering ocean circulation patterns and aiding sea ice growth.
But increasing sea ice is only a small part of the Antarctic story. Scientists have also used satellite observations of the land-based ice sheet to measure whether the Antarctic ice sheet has been losing or gaining ice.
Attempts to answer the question came up with estimates ranging from an increase of about 100bn tonnes of ice per year since the 1960s to a loss of 200bn tonnes a year over the same period. However, more recent reports agree that the ice sheet is losing ice – and indeed that the rate of loss has been speeding up.
Ice loss is not uniform over the whole of the ice sheet. Eastern Antarctica was initially found to be relatively stable, with most of the ice being lost in Western Antarctica, particularly around the Antarctic Peninsula. These regional differences in ice loss fit with the pattern of temperature change over the ice sheet.
• This article was written by Carbon Brief in conjunction with the Guardian and partners
Humanity’s greenhouse gas emissions may be acidifying the oceans at a faster rate than at any time in the last 300 million years. The sheer speed of change means we do not know how severe the consequences will be.
Bärbel Hönisch of Columbia University in Palisades, New York, and colleagues used the chemical record preserved in rocks to gauge previous ocean acidification events.
The best match for current changes was the Palaeocene-Eocene thermal maximum of 55 million years ago, when vast amounts of methane were released into the atmosphere causing rapid global warming, ocean acidification, and mass extinction. But even then, it took at least 3000 years for ocean pH to drop by 0.5. “That is an order of magnitude slower than today,” Hönisch says.
The 300-million-year period that Hönisch and colleagues studied includes the biggest extinction of them all: the end-Permian extinction. This event, 252 million years ago, wiped out up to 96 per cent of marine species. But it probably had other causes.