Antarctic Rate of Ice Loss Double Previous Estimate
For the third time this month there is bad news about ice melt in Antarctica. This time with consequences we will experience very soon.
First we had the news that a small plug of ice is holding back vast glaciers in East Antarctica’s Wilkes Basin. If the plug goes melting in that region will become unstoppable, adding 3-4m to the sea level rise already factored in from other causes. A week later there was the news that some West Antarctic glaciers have already passed the point of no return, and will melt faster than previously thought.
While the first study is apocalyptic in its implications, little of the damage is likely to be seen this century – the worst could be a thousand years away. The second will raise sea levels by less, but on a shorter timescale. It can, though, still be ignored by those who, in John Oliver’s words “cannot be trusted with the future tense.”
However, the Centre for Polar Observation and Modelling at Leeds University has found that ice loss is happening right now, and at twice the rate estimated using an incomplete version of the same technique.
The European Space Agency’s Cryosat spacecraft uses radar to measure the height and extent of the Antarctic and Greenland ice sheets. Geophysical Research Letters reports the Leeds team found 159 billion tonnes is disappearing each year, 134 billion from West Antarctica, 23 billion from the Antarctic Peninsular and 3 billion from East Antarctica. While East Antarctica contains the most ice, and therefore will be most influential in the very long run, for the moment it is West Antarctica, and particularly the glaciers flowing into the Amundsen Seat, that is causing the problems.
Previous studies had only been able to map portions of the continent, forcing extrapolations to the whole. Cryosat can penetrate obscuring clouds, allowing the team 96% coverage, leaving out only a small ring around the South Pole. The uncertainty is ±81 billion tonnes.
“We find that ice losses continue to be most pronounced along the fast-flowing ice streams of the Amundsen Sea sector, with thinning rates of between 4 and 8 metres per year near to the grounding lines of the Pine Island, Thwaites and Smith Glaciers,” says first author Dr Malcolm McMillan.
“Although we are fortunate to now have, in CryoSat-2, a routine capability to monitor the polar ice sheets, the increased thinning we have detected in West Antarctica is a worrying development,” says team leader Professor Andrew Shepherd. “It adds concrete evidence that dramatic changes are underway in this part of our planet, which has enough ice to raise global sea levels by more than a metre. The challenge is to use this evidence to test and improve the predictive skill of climate models.”
The observed melting is raising sea levels by 0.45mm/year. While this accounts for only one seventh of the observed increase in ocean levels, it is particularly disturbing because the Antarctic contribution is much more likely to accelerate than growth from most other sources.
The findings go some way to resolving a contradiction between past, incomplete, altimeter measurements of ice loss and those produced by other techniques. The loss observed is consistent with on the ice observations that have found one glacier losing 9m a year.
NASA has provided the following animation to show how warmer waters off the continent lead to glacier retreat.
Photo: Anna Hogg. Researchers at the Centre for Polar Observation and Modelling conduct research on the Antarctic Ice itself, as well as using satellite data to measure ice loss.