Walling ourselves in

wallsHow can we avoid a future that looks like this? Image credit: Pixabay

If you were to ask a non-scientist what the biggest impact of climate change would be, I’d wager that sea-level rise would be amongst the most common responses. Even though the impacts are likely to be wide-ranging and distributed across the globe, both inland and near coastlines, rising waters swamping coastal communities and drowned islands are perhaps some of the most visceral images that climate change can conjure. After all, the ice gradually melting below the picture-postcard polar bear has to end up somewhere.

It’s not without good reason, either. A large proportion of the world’s population lives close to the coasts, and researchers estimate hundreds of millions are exposed to sea-level rise in low-lying regions. Moreover, two thirds of cities with greater than 5 million inhabitants in low-lying coastal regions, and the demographic shift from rural areas to cities will only serve to increase the number of people at risk from sea level rise in future.

Even if the global economy can rapidly transition to a low-carbon future, some amount of sea-level rise is bound to occur, both as a result of thermal expansion of water and melting ice sheets. The rate at which this will occur is not entirely clear, but estimates suggest anywhere between 2 and 5 feet of sea-level rise averaged around the globe by 2100. Waters rising that high could not only flood some cities outright, but also put a much larger number of cities and communities at risk from storm surges and tidal flooding.

Up to this point, many readers will have heard some version of this before. I’d argue that the more important question, that is much more seldom discussed, is: What happens when the waters rise?
Cities will flood, we’re told – but is that realistic? We may not be able to change how much the sea rises, but can we prevent the waters from encroaching upon our cities and towns? It’s not unheard of for cities to have widespread flood defences, or even dykes such settlements are below sea level. Much of the Netherlands is below sea level in this respect; is it realistic to ask if this might be what we face in the future as seas rise?

Scientists have explored this in recent years and the answer is complex. Some research suggests that it may indeed be cheaper to construct walls than to abandon coastal cities wholesale, but this has to be considered in the context of diverse global economies. Developed countries are probably able to afford construction of such flood defences, but what about countries like Bangladesh, or low-lying islands; they may lack the financial wherewithal to even have a choice in the matter.

Even in developing countries, the impacts of walls to keep out the sea may be more broad than we currently consider. Some advocates of a technological solution might point to Venice as an example solution; giant flood gates now surround the city to protect the lagoon from flooding in extremely high tide events, but there are other, less encouraging examples. In Japan, after the devastating tsunami in 2011, huge sea-walls were erected along much of the affected coastline, as a barrier to prevent future events of the same ilk. Local residents report feeling walled-in by this barrier; should we expect similar psychological issues to arise in residents of cities protected from rising seas by walls?

Perhaps even more relevant than being walled-in are those who might be walled-out. In those countries where building flood defences is not financially feasible, retreat will be the only option from rising seas. Retreat perhaps understates that this could mean large-scale migration of threatened communities; the geopolitical climate in many Western countries at present could hardly be described as pro-migration, and it’s conceivable to imagine a future where cities in developed countries build walls both physically to keep out the oceans, and legally to keep out those vulnerable migrants.

Unfortunately, sea-level rise is almost guaranteed to be a problem we’ll have to face, making these issues a very real dilemma. However, there are alternatives to walls and migration; careful management of coastlines and integration of natural ecosystems may in some places limit the potential for tidal flooding. Sand dunes and wetlands can blunt flooding from tidal swells and limit inland impacts; coastal geologists will be vital to understand where and how to apply conservation strategies. We know that wetlands flora can adapt to changing sea levels, but with the rapid rise predicted by some researchers, we need to learn quickly quite how fast they can adapt, and whether we can help in these scenarios. Ecologically sound planning of our changing coastlines should be of paramount importance; it offers a less closed-in future than walls built around our cities and coasts.

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