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The Antarctic ice sheet is around one and half times larger than Australia. What’s happening in one part of Antarctica may not be the same as what’s happening in another – just like the east and west coasts of the US can experience very different responses to, for example, a change in the El Niño weather pattern. These are periodic climate events that result in wetter conditions across the southern US, warmer conditions in the north and drier weather on the north-eastern seaboard.
The ice in Antarctica is nearly 5km thick in places and we have very little idea what the conditions are like at the base, even though those conditions play a key role in determining the speed with which the ice can respond to climate change, including how fast it can flow toward and into the ocean. A warm, wet base lubricates the bedrock of land beneath the ice and allows it to slide over it.
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What the experts say
Fortunately, models are not the only tools for predicting the future. Structured Expert Judgement is a method from a study one of us published in 2013. Experts give their judgement on a hard-to-model problem and their judgements are combined in a way that takes into account how good they are at assessing their own uncertainty. This provides a rational consensus.
The approach has been used when the consequences of an event are potentially catastrophic, but our ability to model the system is poor. These include volcanic eruptions, earthquakes, the spread of vector-borne diseases such as malaria and even aeroplane crashes.
Since the study in 2013, scientists modelling ice sheets have improved their models by trying to incorporate processes that cause positive and negative feedback. Impurities on the surface of the Greenland ice sheet cause positive feedback as they enhance melting by absorbing more of the sun’s heat. The stabilising effect of bedrock rising as the overlying ice thins, lessening the weight on the bed, is an example of negative feedback, as it slows the rate that the ice melts.
The record of observations of ice sheet change, primarily from satellite data, has also grown in length and quality, helping to improve knowledge of the recent behaviour of the ice sheets.
With colleagues from the UK and US, we undertook a new Structured Expert Judgement exercise. With all the new research, data and knowledge, you might expect the uncertainties around how much ice sheet melting will contribute to sea level rise to have got smaller. Unfortunately, that’s not what we found. What we did find was a range of future outcomes that go from bad to worse.
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We gathered together 22 experts in the US and UK in 2018 and combined their judgements. The results are sobering. Rather than a shrinking in the uncertainty of future ice sheet behaviour over the last six years, it has grown.
If the global temperature increase stays below 2°C, the experts’ best estimate of the average contribution of the ice sheets to sea level was 26cm. They concluded, however, that there is a 5% chance that the contribution could be as much as 80cm.
If this is combined with the two other main factors that influence sea level – glaciers melting around the world and the expansion of ocean water as it warms – then global mean sea level rise could exceed one metre by 2100. If this were to occur, many small island states would experience their current once-in-a-hundred–year flood every other day and become effectively uninhabitable.
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| A climate refugee crisis could dwarf all previous forced migrations. Punghi/Shutterstock |
Let’s try and put this into context. The Syrian refugee crisis is estimated to have caused about a million people to migrate to Europe. This occurred over years rather than a century, giving much less time for countries to adjust. Still, sea level rise driven by migration of this size might threaten the existence of nation states and result in unimaginable stress on resources and space. There is time to change course, but not much, and the longer we delay the harder it gets, the bigger the mountain we have to climb.
Links
- Why remote Antarctica is so important in a warming world
- The sea isn’t actually ‘level’: why rising oceans will hit some cities more than others
- Why ice sheets will keep melting for centuries to come
- Heat from the Atlantic Ocean is melting Arctic sea ice further eastwards than ever before
- How Climate Change Is Pushing Central American Migrants To The US
- Climate Change: Global Impacts 'Accelerating' - WMO
- 'Great Concern': World Meteorology Agency Reports Bad Climate Tidings
- Climate Change Creates A New Migration Crisis For Bangladesh
- Climate Gentrification: The Rich Can Afford To Move – What About The Poor?
- Climate Change Must Be Dealt With Before It Unleashes Millions Of Global-Warming Refugees
- Climate Change Could Affect Human Evolution. Here's How.
- NASA: Antarctica's Effect On Sea Level Rise In Coming Centuries
- Climate Change Predicted To Wipe $571 Billion Off Property Values
- What Survival Looks Like After The Oceans Rise
- Climate Change Helped Destroy These Four Ancient Civilisations
- Polar Warning: Even Antarctica’s Coldest Region Is Starting To Melt
- Huge Cavity In Antarctic Glacier Signals Rapid Decay
- An Ocean Of Evidence On Warming Is Our Cue To Take Action - Now
- Warming Oceans Likely To Raise Sea Levels 30cm By End Of Century – Study
- How Extreme Weather Is Shrinking The Planet
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