27 Nov 2014

On Sea Level Rise

On Tuesday night this week, I had the pleasure of listening to Prof David Vaughn talking about the work of the British Antarctic Survey where he has worked almost all his adult life. Vaughn is Professor Ice Sheet and he spends his time exploring the goings on in Antarctica, Greenland and the 200,000 plus glaciers that pepper the world's mountain ranges. It's a fascinating area of science and one that's obviously key to our understanding of where our climate and our sea levels are heading.

At this point, I would expect a number of people to rise angrily from their perches and accuse me of listening to a pinko greenie engaged in a conspiracy to pull the wool over our eyes by manipulating the data to suggest we are all doomed. "British Antarctic Survey? British Alarmist Society, more like." I have no doubt that UKIP will be planning to slash their £44m annual budget under their charming "Axe all green subsidies" policy.

May I suggest that, before they do, they spend an hour listening to David Vaughn talk. He dresses very conservatively, he talks very quietly, he is polite almost to a fault. In fact, he comes on like an accountant, which perhaps is what he is actually is, albeit one with some very sophisticated measuring kit. He just weighs ice and measures sea levels. He looks for trends and patterns and he peers into the future to try and work out where things are headed, but he steers clear of making suggestions about what we should or shouldn't be doing — "that's for economists and politicians to decide".

What was interesting to me is the huge strides that have been made in our knowledge in the past few years, between the IPCC reports AR4 in 2007 and AR5 in 2013. We now have two satellites (the Grace mission) which are measuring gravitational variations caused by changes in mass at surface level. If the mass of an ice cap is changing, Grace will pick it up. Clever stuff.

And the mass of ice sheets is changing. As you might expect, it's decreasing, although the picture isn't  uniform nor necessarily easy to interpret. Thus far, the changes are fairly moderate and are occurring at the margins, but what scientists fear is that there might be a sudden catastrophic event. One area on the Antarctic coast is of particular concern because there the ice sheet rests on bedrock which is far below sea level and there is a possibility that relatively small changes in sea temperature could cause it to all slide into the sea. How big an area? The size of Cornwall? Belgium? Norway? No one knows, but Vaughn probably has a better handle on it than anybody else. If we can afford MI5 and MI6, then I think we can afford the BAS.

Back at the height of the last ice age when ice sheets covered much of the northern hemisphere, the global sea level was 120m lower than it is today. The Mediterranean was not there and there was a land bridge between Britain and France. The temperature was approximately 7°C colder than it is today.

Still locked up in the Greenland Ice sheet is another potential 7m of sea level rise and in Antarctica it's 60m, so if we were to head for a 4°C increase in global temperatures, which is within the bounds of possibility (though far from certain), then we could anticipate a much higher sea level, though it might take 500 years to play out.

What is known today is that global sea level is currently rising at 3.2mm per annum. It the last century, it averaged around 2mm and in the 19th century, they think it was around 0.8mm. There is no hiatus in sea level change — the rise is pretty much constant. 3.2mm may not sound like much, but that still equates to 300mm by 2100. In fact best estimates are rather more than this at present but it's a field open to a lot of doubt and speculation. (Sea level is affected by a number of factors beside ice sheet melt.) It's probable that the relatively small amount of climate warming that we've already seen has locked in sea levels rises of several meters, but the timescale on which it will all happen is contentious.

The questions are can we manage this? Can we arrest it? And over what timescales are we talking? Should we be planning now to mitigate sea level rises which won't be fully played out till maybe the 25th century? What exactly are our planning horizons? This isn't the stuff of blind panic: it's good old risk assessment played out over a very long timescale. It does however ask some very uncomfortable questions about whether our actions now are making things better or worse for our distant descendants and what exactly we are hoping to achieve on Planet Earth.

In the shorter term, what is likely to happen is that storm surge events like the one that accompanied Hurricane Sandy are going to get worse and more frequent, but we already know that our coastal cities (New Orleans) and infrastructure (Fukushima) are at much greater peril than we care to think about. Sea level rise simply changes the odds and, if you like, makes coastal protection more expensive. Right-wing commentators who claim that it's simply too expensive to stop burning fossil fuels should bear this in mind. The longer we keep bingeing, the bigger the hangover.

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