Fifty thousand drowned, steamships aground with their bows among trees, cattle rolled head over heels by gigantic waves — stories of great sea surges from past centuries abound. Many of them cascaded ashore when coastlines were relatively stable, killing everyone in their path. Today, we live in a warming world of rising sea levels, where tens of millions of us live a few meters above the ocean. The potential for sudden cataclysm is greater than ever.
The record of history is sobering. On Jan. 16, 1362, a severe southwesterly storm swept across the British Isles. The wooden spire of Norwich cathedral in eastern England collapsed.
Hours later, the Grote Mandrenke, “The Great Killing of Men,” descended on the Low Countries at high tide. Huge waves carried everything before them. “An infinity of people perished,” fishing fleets became matchwood, entire herds of cattle and sheep perished in the raging waters. Three centuries later, in 1634, another cataclysmic storm surge brought sea levels four meters above normal to the Strand Islands off northern Germany. As many as 15,000 people and 50,000 livestock drowned.
These were but two of the savage attacks on the low-lying coasts of the North Sea, this from a patch of ocean that was largely dry land less than 8,000 years ago. The geologists call it Doggerland, a sunken landscape that once formed the North Sea. It was a land of sluggish rivers, lakes and extensive wetlands. A few thousand hunters thrived there, living off fish and small game, using antler-tipped spears.
We know this because a trawler dredged one from the seabed in 1932. Doggerland slowly vanished in the face of sea level rise caused by thawing ice sheets, an ever-changing world for those who lived there. By 5,500 B.C., Doggerland had disappeared under the chilly waters of the North Sea.
The inhabitants of the Low Countries have been battling the ocean ever since. For over a thousand years, they have tried to wall off the ocean. Today, millions of people live in densely occupied coastal landscapes behind great barriers. The Dutch government’s hideously expensive Delta Works was the culmination of centuries of defense work, but the authorities never relax in the face of a warming future with predictions of more extreme weather events. They are planning for at least 10,000-year storms in a world of rising sea levels.
It’s hard for us to imagine what the world was like at the end of the Ice Age, when sea levels were about 220 meters lower and the North Sea was dry land.
Take the Nile, which flowed into the Mediterranean through narrow gorges. As the ocean rose, the now silt-heavy Nile formed a fertile delta that became the granary of the pharaohs. All was well two thousand years ago, when Alexandria had only 300,000 inhabitants. Today, the Aswan Dam far upstream has drastically reduced silt flow. Nearly 10 million people live in Alexandria and Cairo. The delta is slowly vanishing under rising sea levels, its groundwater contaminated by saltwater, the soils depleted. The delta is no longer a balanced system. Perhaps 7 million people will suffer regularly from starvation by 2100.
The world’s sea levels have risen since the 1860s, with no end in sight. Skeptics argue that this is a long-term problem, measured in centuries rather than generations, that there is plenty of time to adapt to changing shorelines. But they forget about the more frequent extreme-weather events with their sea surges predicted for the future.
Hurricane Katrina in 2005 and Superstorm Sandy in 2012 were both wake-up calls for Americans living near sea level. Katrina devastated New Orleans, leaving 80 percent of the city underwater. Levees broke, over 1,500 people died, and thousands were stranded, especially poorer people. Sandy’s surge flooded Lower Manhattan and the New Jersey Shore. Subways flooded, thousands of houses became rubble. With $60 billion of damage, recovery will take years, while a debate over long-term solutions sputters along. Does one wall off New York, force people to build on higher ground, or restore protective mangrove swamps? The answers will be long in coming, but meanwhile, as cities like Miami grow, our vulnerability increases every year.
The threat is even more ominous elsewhere. Today, some 200 million people live within five meters of sea level, many of them in megacities like Shanghai. The Netherlands has the resources to wall off the sea, but what about other parts of the world? Small Pacific islands like Tuvalu, Alaska’s barrier island communities, and the Maldives in the Indian Ocean are seriously endangered and may even cease to exist.
Bangladesh, most of which is river delta country, lies at the head of the Bay of Bengal, where intense cyclones and their fast-moving storm surges have the potential to kill thousands. And kill they do, in a country with an exploding population, chronic poverty and a long coastline. Cyclone Bhola in 1970 killed over half a million people, at a time when the population was much smaller than today. To its credit, the government has developed early warning systems, erected refuge buildings, and created evacuation strategies that have saved many lives. But these do not answer the longer-term problem of fast-growing urban populations, threats to rice crops, seawater contaminated groundwater, and nowhere to move millions of people forced from their homes by rising seas. More