COP15 and Antarctica: how soon, how fast, how deep?

Torrents of bandwidth have been dedicated to the Paris climate change conference (COP15). I am not an expert, a scientist or diplomat so I’ve focused on one small question. What about Antarctica, the warning canary of climate change?

The standout headline is the commitment to keep global temperatures ‘well below’ 2° above pre-industrial levels and work towards a 1.5° limit. That’s a huge challenge, but a study of the impacts on sea levels soon helps us to understand why this matters.

There is an excellent interactive map at http://geology.com/sea-level-rise/. After you’ve experimented with your own home, take a look at what a 1m sea-level rise does to the Netherlands, Denmark and Bangladesh. It would wipe out many Pacific nations, which is why they have been so vociferous and effective in these discussions. (Remember, these projections take no account of extreme weather events, such as Storm Desmond, which brought flooding to the north of England and Wales this week. The BBC picture above is the valley around Keswick.)

Antarctica, its islands and the Southern Ocean are not mentioned in the new Agreement, but then very few places are. The Agreement itself is about process, binding agreements, shared methodologies and (of course and crucially) money.  Several important events and briefings during COP15 were organized by the Scientific Committee on Antarctic Research (SCAR) and the the International Cryosphere and Climate Initiative (ICCI). You can watch the press briefing on Antarctica Day, 1 December. (Don't be put off by the fumblings of the slide operator.) Prof Julian Gutt (of the Wegener Institute at Bremerhaven), who spoke at that briefing did a useful summary.  The results presented to COP15 are part of the most recent update of the SCAR project on Antarctic Climate Change and the Environment (ACCE) for which there is an excellent wiki which captures ongoing research.

Ice sheets represent a huge proportion of water on Earth. Over 95% of terrestrial ice is locked up in three sheets: Greenland, West and East Antarctica. If Antarctica’s ice melts, sea level rises a catastrophic 55m or more. That makes the current huge movement of people into Europe look like nothing. So let’s take a look at what’s happening to glaciers. There are three major points, and they all matter to the target of 1.5°.

First there’s the bleedin’ obvious: melting ice puts a lot of water into the sea. The Greenland Ice Sheet alone represents an additional 7.3m on sea levels. Each little glacier doesn’t always sound like much but start adding those together and you see plenty. (Of course the sea level rise isn’t the only impact of melting glaciers: I’ve talked elsewhere about some of the ecosystems impact of more sediment for example.)

Even relatively small areas can have a big impact because of the way the watersheds work in the underlying bedrock and its contours. Several big glaciers, particularly Thwaites, Pine Island and Smith,  empty into the Amundsen Sea (Look about 30° anticlockwise from the Peninsula and it’s that big bay). These alone are estimated to contain enough water to raise sea levels by about 1m. This is a really inaccessible area (even by Antarctic standards) but recent research shows these glaciers are retreating rapidly. Dr Gabrielle Walker, in her wonderful survey of continental science, Antarctica, describes the process: the warmer deeper water surrounding Antarctica used to be held away from the Thwaites glacier tongue by a ridge. The ice over the ridge has melted and now that warm water is ‘hollowing out a huge cavity, like a rotten tooth.’

Secondly, the rate of change is extremely difficult to predict. The Antarctic ice, in particular, has already melted faster than modelling just a few years ago.  This suggests complex feedback loops and mechanisms we are only just now beginning to understand.

This slide (taken from fourth Assessment Report for the International Panel on Climate Change and discussed at COP15 by Prof Bamber at Bristol University) shows the increasing rate of ice-mass loss across the three big ice-sheets. With data aggregated across 5 year intervals since reliable satellite observation began in the early 1990’s, we can see that the ice is disappearing. The loss is accelerating and we don’t yet really understand why.

Scientists are now talking a great deal about the grounding line, the point at which the glacier moves from land to sea: how does this hinge influence a glacier's stability and rate of melting? On all three ice sheets on many glaciers it is retreating rapidly. The speed of retreat is also affected by the slant or slope of the bedrock beneath the ice itself, particularly where the land slopes downwards as it goes inland. In the Amundsen sea, for instance, there are models which suggest a huge loss of ice by 2200 as a result of the movement of the grounding line across the steep valleys of the underlying bedrock, as this slide illustrates. 

Crucially, in some places a huge area of ice is protected from the sea by one (relatively) small ice plug. The Wilkes Basin on the East Antarctic Ice Sheet is fed by the largest such basin in East Antarctica. If it melted it alone would increase sea-levels by between three and four meters. The edge of that glacier is protected from the sea, and hence rapid erosion, by an iceplug. The plug itself itself only contributes 80mm of SLR, but take it out and we will see rapid impact. The next slide shows the scale of the bay which would be created by glacial loss at Wilkes.

You can also see that we are talking a long time scale, but it is already starting. The rate of ice-melt really matters. Prof Bamber said 'If it's a millimetre a year, which is 10 centimetres a century, we can adapt to that. In a thousand years from now, who knows what capacity we'll have to cope with that. But if it's 10 times that, if it's a centimetre a year, we have really, really big problems.' This isn't standard apocalyptic talk, based on political prognostications or magical thinking, but a sober and possibly conservative evidence-based hypothesis. 

Thirdly, these changes are irreversible and they go through a tipping point, a step change where even a bit more sea ice at the fringes makes very little difference. Some scientists fear that tipping point has already been passed with the glaciers feeding into the Admundson Sea and the Greenland sheet, which together represent about 8.3m rise in sea level. (Feel free to go back and look at that interactive map again. Consider Cairo and Basra.)

In Paris Antarctic scientists have been anxious to say that they don’t see these changes happening tomorrow. They are estimating centuries for the sea ice to melt, even if all fossil fuel on earth was put into the atmosphere. At the same time, though, they are clear that we must start planning now. Prof Ricarda Winkelmann of the Potsdam Institute for Climate Impact Research (PIK), in Germany said at the 1 December press conference that ‘We really need to think of sea level rise as a commitment, and we really need to decide what our legacy is supposed to be.’

You often see the 2° target (agreed at the Copenhagen conference) described as ‘arbitrary’. Bear in mind that in 2015, global average temperature is expected to reach the 1° increase for the first time. Whatever some die-hard American Republicans and our own Nigel Lawson might argue, the evidence of warming is crystal clear.

So does 1.5° matter and does it have any more real meaning beyond protecting a few flyspeck states in the Pacific expanse? The models suggest, with all the caveats and unknown mechanisms duly acknowledged, that at temperatures 1.6° above pre-industrial levels the whole of the Greenland ice sheet will be gone. That’s 7.3m on the sea level and it is likely that we are already committed to that happening. Yes, that number really matters.

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