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Ice sheet melt rate underestimated

The West Antarctic Ice Sheet The West Antarctic Ice Sheet NASA
11 Mar
2015
The West Antarctic Ice Sheet contains enough ice to raise the global sea level by 16 feet, and it could be melting faster than previously thought

Researchers have long agreed that the vast West Antarctic Ice Sheet will collapse. Up until now the question has been whether it will take decades or centuries.

However, a new model from Caltech suggests that the collapse will come sooner than previously thought, with the potential to raise global sea levels by 16 feet.

Antarctica’s ice sheets are an unknown factor in global climate change. Scientists know that rising atmospheric and ocean temperatures damage the ice sheets, but nobody is sure how fast each sheet will melt.

Last year, a study suggested that the fastest possible melt rate would be 200 years with the slowest at more than a millennium, with 200–500 years being the most likely scenario.

‘All of our simulations show it will retreat at less than a millimetre of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go,’ said Ian Joughin, a glaciologist at the University of Washington, commenting on last year’s research.

us vs antarcticaUS and Antarctica compared (Image: NASA)

The new research shows the ice sheet’s physical features make it particularly vulnerable to global warming. The sheet’s grounding line, where the land ice meets the ocean, is particularly vulnerable.

‘Our results show that the stability of the whole ice sheet and our ability to predict its future melting is extremely sensitive to what happens in a very small region right at the grounding line,’ says Andrew Thompson, a co-author on the study.

A slope on the ocean floor directs warm water to the ice sheet’s base to melt the sheet from below.

Life on ice. A tour round the US Antarctic Program’s West Antarctic Ice Sheet base

The scientists think that as the grounding line retreats, interior ice flow into the oceans could increase. Grounding line recession also thins and melts ice shelves, which are floating extensions to an ice sheet that reduce ice flow into the sea.

Previous research took a simplified approach to measuring ice melt that did not account for friction at the grounding zone. The new model takes inspiration from earthquake research to improve predictions.

‘If another sudden switch happens in West Antarctica, sea level could rise a lot, so understanding what is going on at the grounding lines is essential,’ says Richard Alley, a glaciologist at Pennsylvania State University.

Once the new model has been applied to the ice sheet, scientists will be able to tell just how much sooner change will take place.

The research was published in the Journal of Glaciology. Read it here.

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