A new approach to assessing future sea level rise from ice sheets

Jan 06, 2013

Future sea level rise due to the melting of the Greenland and Antarctic ice sheets could be substantially larger than estimated in Climate Change 2007, the Fourth Assessment Report of the IPCC, according to new research from the University of Bristol.

The study, published today in Nature Climate Change, is the first of its kind on ice sheet melting to use structured expert elicitation (EE) together with an approach which mathematically pools experts' opinions. EE is already used in a number of other scientific fields such as forecasting volcanic eruptions.

The ice sheets covering Antarctica and Greenland contain about 99.5 per cent of the Earth's which would raise by some 63m if it were to melt completely. The ice sheets are the largest potential source of future – and they also possess the largest uncertainty over their future behaviour. They present some unique challenges for predicting their future response using numerical modelling and, as a consequence, alternative approaches have been explored.

One such approach is via carefully soliciting and pooling expert judgements – a practice already used in fields as diverse as eruption forecasting and the spread of vector borne diseases. In this study Professor Jonathan Bamber and Professor Willy Aspinall used such an approach to assess the uncertainties in the future response of the ice sheets.

They found that the median estimate for the sea level contribution from the ice sheets by 2100 was 29cm with a 5 per cent probability that it could exceed 84cm. When combined with other sources of sea level rise, this implies a conceivable risk of a rise of greater than 1m by 2100, which would have deeply profound consequences for humankind. The 's report provided figures ranging from 18cm to 59cm for six possible scenarios.

The researchers also found that the scientists, as a group, were highly uncertain about the cause of the recent increase in ice sheet observed by satellites and equally unsure whether this was part of a long term trend or due to short-term fluctuations in the climate system.

Professor Bamber said: "This is the first study of its kind on ice sheet melting to use a formalized mathematical pooling of experts' opinions. It demonstrates the value and potential of this approach for a wide range of similar problems in research, where past data and current numerical modelling have significant limitations when it comes to forecasting future trends and patterns."

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More information: 'An expert judgement assessment of future sea level rise from the ice sheets' by J.L. Bamber and W.P. Aspinall in Nature Climate Change.

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Dug
2.3 / 5 (3) Jan 06, 2013
To date both climate change and sea level computer modeling have been abysmal at predicting current and future rises. When you run the models backwards they can't predict what has happened in the past using all available indicators. So now, we're going to make predictions by popular opinion? One has to assume that they expect that to be better than current computer climate modeling predictions... oh, but wait those expert opinions are based on... current computer climate modeling. GIGO
slack
1 / 5 (2) Jan 07, 2013
:)
Aahh well, it had to happen...
Science by the numbers after all, too bad the numbers just represent opinions!
And why use opinions?
Why, because: "... past data and current numerical modelling have significant limitations when it comes to forecasting future trends and patterns."
LOL!

But that doesn't deter the determined sensationalism of the editor of this piece, which has, in the synopsis (which is all that most casual readers absorb):
"Future sea level rise due to the melting of the Greenland and Antarctic ice sheets could be substantially larger than estimated in Climate Change 2007..."

In spite of the fact that the article actually states:
"The researchers also found that the scientists, as a group, were highly uncertain about the cause of the recent increase in ice sheet mass loss observed by satellites and equally unsure whether this was part of a long term trend or due to short-term fluctuations in the climate system."

But that never stops the determined alarmist... :)
antialias_physorg
5 / 5 (2) Jan 07, 2013
To date both climate change and sea level computer modeling have been abysmal at predicting current and future rises.

It has?

CNES/CLS, Ablain, White, CUSLRG, and LSA all have sea level rises of between 2.9 and 3.2 mm per year.
Sattelite data shows that the actual rise was 3.3 mm per year. So I'd say they have done a pretty good job of estimating sea level rise for the most part.

That someone is "highly uncertain about the cause of the recent increase in ice" doesn't mean that they can't model it based on past observations.

You can model a trend by fitting a curve to past datapoints - even if you don't know the mechanism. Unless the mechanism is HIGHLY non-linear such a model will be good for short term to medium term predictions. (For example ancient cultures were pretty good at predicting the movement of stars/planets - even though they had no idea about the mechanism behind it)