Retreat?

So now it's time to say goodbye! After having spent the last couple of months, while writing this blog, looking at what we are dealing with in terms of sea level rise, and the some of the ways we are trying to cope with the problem. I've really been struck by the extent of the problem that we are faced with. While it will effect some coastlines alot more than others, this is definitely a global problem.


I've looked at a range of possibilities from man made to natural that can help protect our coastlines, but the over-riding impression that I get is that long run these cannot help us. I've started to wonder whether it is ever really possible to mitigate for sea level rise in the long term or whether we are just putting off the inevitable For some areas I think that in the long run (and I don't even mean that far into the future) retreat is the only option. Future projections include considerable sea level rise, and I for one am not sure I would feel comfortable living behind a sea wall or dyke and below sea level.


Already some communities are facing up to the possibilities of relocating. Many island nations in the Pacific have already been forced to abandon some of the lower lying islands, and communities in Alaska are considering moving inland after increased storms and coastal erosion (Kelman, 2008). Of these Tuvalu is perhaps the most at risk, but they are also the only ones with a plan - when Tuvalu is finally submerged the Tuvaluans can have a home in New Zealand. This is not the case for all the island nations, others such as Vanuatu, and the Cook Islands have no such safety net in place. This brings up the really interesting question - whose responsibility is it to re home these communities? And then there are also all the communities that won't be washed away but rising sea level could destroy their way of live, and their livelihood. These will be the majority - how can we look after these people too? Relocating comes with problems too - one village in Alaska voted to move inland after higher sea levels and storms were threatening to destroy their houses. But having announced their intentions they were no longer able to secure funding for important infrastructure such as hospitals and schools (GRIST). It's really important that these people don't become refugees in another country, and that it is possible to find a new home where they can keep their sense of community rather than being spread about and swallowed up by another country.

I've also been thinking - to what extent is this a problem of our own making? We have released unprecedented volumes of greenhouse gases into the atmosphere causing warming, and ice melting and thermal expansion. But we have also situated many of our largest population centres next to the coast making them unnecessarily vulnerable to any small changes in sea level whether it be from natural variability, or from anthropogenic causes. Never before in human history have our numbers been so many, our populations been so static, and it been so difficult for us to relocate to higher ground.

Credits: Nick Lyon

 

So what would Canute do? This is the thing about King Canute, he never actually thought he could hold back the sea. He only sat on the beach and told the sea to stay back as a way of proving to his courtiers that he was not all powerful, and could not control nature. Perhaps this lesson from a thousand years ago is worth remembering as we move forward. We cannot control nature, and perhaps it might be better to use our resources to look after ourselves rather than holding back the sea.

Future Sea Level Rise

I've spent the last couple of months looking into the various reasons for sea level rise, so I think it's high time (or high tide?) I put all this together and consider how the sea level could change in the future.

This looks like a worst case scenario for King Canute (Credit: Henry Tapper)

Scientists have varying degrees of confidence in each component of sea level rise, and for a long time all the different causes could not explain the extent of sea level rise we were observing - until groundwater was included that its. Even as it is, the melting of ice sheets have the highest potential to increase sea level - perhaps global mean sea level rise of up to 70 metres, but ice sheet dynamics aren't fully understood yet (Rahmstorf, 2007), so as you can imagine it is very very difficult to predict how sea level is going to change in the future. So let's start with the IPCC AR5. They state:

"It is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971-2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets."

 

This is very important because even the RCP2.6 scenario, in which emissions stabilise and then start to decrease before 2100 (van Vuuren et al. 2011), involves increased sea level rise. You can see this more clearly on the graph below. So even if we do everything we can in terms of reducing our emissions, models agree that we will experience continued sea level rise of at least 30 cm by 2100.

Projected sea level from the RCP2.6 and RCP8.5 scenarios relative to 1986-2005 from the CMIP ensemble (IPCC)

I think in terms on the way a warming climate will impact on our lives, increasing sea level is arguably the biggest problem that we are going to have to deal with. You can start to get an idea of the extent small sea level rises will effect us here. Just taking a look at some of the countries I've already looked at and a 1 metre global sea level rise, it's really quite scary the extent of the problem. So forward planning, mitigation, and adaption are essential. But how reliable can any projection of sea level rise be?


Rahmstorf et al. (2007) compared model projections from the 2001 IPCC report with subsequent observations of sea level. The models, which began in 1990 and didn't incorporate any sea level observations after this date, consistently underestimated global mean sea level rise between 1990 and 2006, despite accurately predicting other aspects of the climate system such as carbon dioxide. Church et al. (2013) suggests that this could be natural variabilty, such as the 60-year sea level oscillation proposed by Chambers et al (2012), not recreated by process based models, rather than a systematic misrepresentation of the climate system. Models have advanced considerably since, alongside out understanding of the climate system, and computer power allowing inclusion of more processes, but it's still worth remembering that all models are wrong - they can only be an indication of future change. With any projection we should always bear their limitations in mind.


So we are pretty sure global mean sea level is going to rise, but it's a bit hard to comprehend the effect this will have on us. I think it's really important to look at the impacts on a more personal regional level. We don't expect sea level to rise uniformly all over the world - things like salt content, ocean dynamics, and post glacial isostatic rebound mean that sea level changes differently all over the world. Some countries will experience accelerating sea level rise, while others will experience falling sea level despite the trend in global sea level. It's all about being prepared, if this is something you are interested in, definitely check out Yuchao's blog on the future economic impacts of sea level rise.

Windmills

I think it's about time to take a brief look at how the Netherlands are coping with rising sea level. The Netherlands are famous for their low topography, half the country is less than one metre above sea level, and the highest point in the Netherlands is actually in the Carribean! Because of this the Dutch are the experts of mitigating against sea level rise, I mean I've been reading the IPCC's Assessment Report 5 ALOT recently, and I can't help but notice that 10/57 of the contributing authors for the sea level change chapter are from the Netherlands. Everyone knows about that little Dutch boy with his finger in the dam, but somehow I don’t think that's the secret of  the Netherlands' mastery of keeping the sea at bay.



Source: Flexitreks



The Netherlands is really interesting because not only do they have many types of coastal defence, but they have also been actively reclaiming land from the sea for hundreds of years. I want to use this post to look at windmills, for some reason I was convinced that these were an intrinsic part of the tulip growing process, but actually windmills have been instrumental in allowing the Dutch to live below sea level. This is definitely something that more countries and cities will have to start considering in the future.


It all started hundreds of years ago when the Dutch started draining marshland to make more farmland. They built canals and ditches to drain the land into rivers, but the land started to subside until it was the same sort of level as the rivers, and didn't drain any more and very liable to flooding (van Schoubroeck, 2010). Obviously this was a bit of a problem a so they made dykes to protect their land from the rivers, more ditches to divert the water, and windmills to pump the water out of the new farmland, to somewhere less annoying, usually a storage lake. The windmills either used a scooping wheel or an Archimedes screw to get the water to higher levels. This was the start of the typical polder system. I have found a little diagram here:



How windmills get water to go uphill (Source: iamexpat)



A really good example is Kinderdijk, a village below sea level that built 19 windmills, together with a combination of ditches and sluices, in the 18th century to pump water out of the land into a storage basin higher up. Who knew all you needed was a bit of wind and an Archimedes screw to live below sea level?


Sadly, the original wind-powered water pumps are no longer in use - but their steam then electrical pumping station descendants are still essential all over the Netherlands. In fact the Dutch pumps are so good, that when the Somerset levels flooded last year the Environment Agency borrowed 13 to try and reduce the water level (BBC News).

 

I love windmills, and I think that it's fantastic that it's possible to live several metres below sea level with a bit of ingenuity and wind power. I'm sure that something along these lines could be used elsewhere - I mean they have certainly proved that they work.