The West Antarctic Ice Sheet “Collapse”
Despite having local unstable regions Antarctica has more sea ice surrounding it than for many years, with more ice being added than is being lost by glaciers in the West Antarctic.
The media have been saying that the collapse of the West Antarctic glaciers is unstoppable; nothing can halt their retreat, say the headlines. They add that man-made climate change is one of the driving factors that will result in sea-level rises that will alter the coastlines of the world.
The media reports are based on two new studies, or rather the press releases associated with them. One of them looked at 40 years of data. The glaciers in the Amundsen Sea sector of West Antarctica “have passed the point of no return,” according to glaciologist Eric Rignot, of UC Irvine and NASA’s Jet Propulsion Laboratory in Pasadena, California. The other study investigated nearby Thwaites glacier saying it will likely disappear in a few centuries.
It’s clear that this region is currently the most changeable part of Antarctica, but it’s not clear why, or how long it will go on for. Not every change seen in the past few decades (when we started obtaining reliable satellite data for the first time) is down to mankind.
The most famous and most studied glacier in the region is Pine Island. It has seen significant changes in the last few decades. Its velocity has increased by 40% between 1996 and 2007 and its grounding line retreated by about 1 km/yr between 1992 -2011. It seems that the grounding line – the boundary where a glacier touches the sea floor – is retreating allowing warm water to melt the glacier from below. This was seen for the first time in the 1990s. Since 2009 however there is some evidence that the glacier has been receding at a steady pace.
Because this region of glaciers rests on land below sea level, and there is no land formation to hold it back it is postulated that a runaway process will eventually cause the entire glacier to discharge out to sea, if things continue as they are. Timescales are important. The “collapse” of this particular ice sheet could happen in 200 years, or more likely in 500 or a thousand or more. One should be careful extrapolating hundreds of years into the future from just 20 years of data. The experience from the glaciers in Greenland is that you have to monitor them for much longer to see how variable is their output. “Rignot said, “It happened many times before when the Earth was as warm as it is about to be.” So the collapse needs the current conditions to last hundreds of years. Is that likely?
It’s all too easy to see such changes as obviously manifestations of man-made climate change. Mankind may have played a role. There is some evidence that ocean current changes induced by ozone depletion (down to us) have brought more warm water southward particularly affecting the Antarctic Peninsula.
The most relevant research, not mentioned in the recent media reports, that helps put the changes seen in this particular region into context is a study of the region’s glaciers over the past 8,000 years. The study showed that Pine Island Glacier has experienced rapid thinning in the past and that once set in motion the rapid changes can persist for centuries, and eventually reverse, without mankind’s help.
So this event occurs naturally and has happened before. Of course we are now more vulnerable to such changes that we were in the early Holocene and should monitor the area and make plans. It is an example that even without any human changes to the climate we humans will still have to adapt to climate changes, potentially big ones.
The ice discharge from Pine Island Glacier could rise to 130 GT/yr and lead to significant sea-level rise, perhaps over a metre. It’s a good thing that the vast majority of the 27 million GT of total Antarctic ice is stable.
Despite having local unstable regions Antarctica has more sea ice surrounding it than for many years, with more ice being added than is being lost by glaciers in the West Antarctic. Sea ice is however not the same as land ice. Sea ice is more variable and does not contribute to sea-level rise. No one really knows why the Antarctic sea ice is expanding, undermined as it is by the very same warm water that is said to be responsible for the increased glacier flow in the West Antarctic.