Rising sea levels: Survival tips from 5000 BC

Catherine Brahic, New Scientist 25 May 09;

WITH rising seas lapping at coastal cities and threatening to engulf entire islands in the not-too-distant future, it's easy to assume our only option will be to abandon them and head for the hills.

There may be another way, however. Archaeological sites in the Caribbean, dating back to 5000 BC, show that some ancient civilisations had it just as bad as anything we are expecting. Yet not only did they survive a changing coastline and more storm surges and hurricanes: they stayed put and successfully adapted to the changing world. Now archaeologists are working out how they managed it and finding ways that we might learn from their example.

The sea-level rise that our ancestors dealt with had nothing to do with human-induced climate change, of course: it was a hangover from the last ice age. As the massive ice sheet that lay on North America melted, the continent was buoyed upwards. As a result, the northern Caribbean, on the other end of the same tectonic plate, sank, making seas in the region rise up to 5 metres over 5000 years.

Although the cause of this rise was very different to what we face today, the effects were probably the same. Rising waters not only nibble away at coastlines, they also mean that hurricanes and storm surges reach further inland. Higher seas also mean that groundwater becomes contaminated with salt, and as the water table rises the waterlogged land becomes more likely to flood.

Despite these changes, excavations of ancient houses in what is now the province of Ciego de Avila in northern Cuba suggest that the region was inhabited between 5000 BC and just 300 years ago. One of the best-preserved ancient sites is the village of Los Buchillones (see image), now 150 metres out to sea, which was inhabited from AD 1260 until the mid-1600s by people known as the Taino. For Jago Cooper, an archaeologist at the University of Leicester, UK, who studies the site and others across the Caribbean, the village provides a rare chance to study the pinnacle of Taino knowledge (see image). "The people at Los Buchillones represent a way of living that capitalises on hundreds or even thousands of years of experience of living in the area," he says.

See the archaeologists at work here and here

So how did they survive as the waters rose? The first clue comes in the proverbial wisdom that every real estate agent knows: location, location, location. Palaeoclimatologist Matthew Peros of the University of Ottawa in Canada and his colleagues have taken sediment cores between the modern shore and the remains of the village, and these show that houses in Los Buchillones were built on stilts over a lagoon (see image). The land barrier that lay between the lagoon and the ocean would have provided the village with some protection from storm surges. Other settlements in the area were in similarly protected pockets, or built on the leeward side of hills.

Building in sheltered spots may seem an obvious precaution, but Cooper argues it's a crucial bit of know-how that the region has since lost. Modern towns and cities, he says, tend to be in more vulnerable, exposed places.

Perhaps surprisingly, building over water may also have made the homes less at risk of flooding. While living in the hills or on higher ground inland may seem a safer bet as the coast becomes less predictable, flood water rushing down hillsides during storms can destroy even the sturdiest house. Building over the lagoon meant that flood water, whether rushing in from the sea or down from the land, could pass underneath the house, minimising damage. This approach seemed to work: radiocarbon dating of Taino posts has shown that they were in place for hundreds of years. What's more, the bark is still on the posts, which tells Cooper that they had never been knocked over and reset. "Unless you're an archaeologist, you can't remove them from the mud without the bark coming off," he says. Older coastal sites elsewhere in the Caribbean have evidence of similar posts, suggesting that the locals may have developed stilted architecture over the centuries to deal with the fickle elements.

While the stilts were deliberately sturdy (see image), the rest of the house was quite the opposite. In 1998, a team led by David Pendergast of the Royal Ontario Museum in Toronto, Canada, unearthed the remains of an entire Taino house, with beams, rafters, roof timber and the palm leaves that made up the house's thatch all collapsed on top of each other.

Living in flimsy, thatched, wooden houses may seem a bad choice, given the extreme weather the Taino were exposed to, but it could actually have been a sensible strategy. Before the arrival of Europeans, villages were often sited close to caves. Because the same caves are used as storm shelters today, archaeologists speculate that the ancient people abandoned their homes for the caves when conditions got too dangerous to stay put. When the storm had passed, they could go home and rebuild, replacing lost thatch and beams within a couple of days, says Cooper. By contrast, modern houses in Cuba are made of concrete or brick, making them expensive and laborious to rebuild after a hurricane.

Clearly, convincing coastal populations to abandon their homes and possessions when a storm appears is unlikely to be popular today. Even so, there are lessons to learn from this style of building. Houses built on sturdy stilts could allow people to remain on the coast in spite of rising sea levels, provided that safe havens built further inland could house the entire population in a storm. This approach has begun to be used in the Maldives after the 2004 tsunami made 20 islands in the archipelago uninhabitable (New Scientist, 9 May, p 37)Movie Camera. Using local materials to build houses would also make them cheaper and easier to rebuild.

Homes, of course, are only one part of what it takes to maintain a civilisation. People need food too. Cooper and his colleagues have found evidence that, along with growing crops, and collecting shellfish and other marine food, the Taino gradually diversified their diet, fishing in new areas and trading food with inland villages. Widening their food options in this way may have acted as insurance when times got tough.

Other civilisations in the region took a different approach. In Belize, rising sea levels meant that some regions were completely transformed. Pollen and ash remains show that 2000 years ago the Mayans were growing maize with slash-and-burn agriculture in some areas that over the course of later centuries became permanently flooded wetlands. Despite this, the people stuck around and, amazingly, continued to grow their crops. They did this by digging huge networks of drainage channels and raising their fields so that roots sat above intruding seawater. Some researchers speculate that they made the best of a bad situation by catching fish, and hunting turtles and waterfowl from the canals.

There are useful lessons here, says Tim Beach of Georgetown University in Washington DC, who has studied the Mayan channels. "There is little doubt we will have to adapt to sea-level rise, and the Maya did it with wood and stone tools," he says. "These are low-cost approaches that developing countries may want to use, where they cannot afford dams and dykes to keep out the sea."

Of course, we now have several advantages over these ancient communities. In place of stone tools we have industrial machinery. In place of the spirits the ancient Taino used to help forecast storms we have live satellite forecasts. But for all our modern technology, as the sea threatens to reclaim the coasts once again, we may have much to learn from the ancient people who took it all in their stride.

Catherine Brahic is New Scientist's environment reporter