Life is becoming more and more unbearable in many areas of flood-prone cities, such as Ho Chi Minh City, where high tides can cause floods for as many as 10 days per month. Sandbags are often ineffective because the water comes up into the house through the sewage systems.
What’s the solution? Some cities are investing in new sea walls, dykes and polders, or high-tide gates – like London’s Thames Barrier – to hold back high waters. In poorer places, people simply endure the problem until they are forced to abandon their homes.
Insurance is already a big problem in many coastal cities. The US government had to underwrite policies for residents of New Orleans after their city was inundated in the aftermath of Hurricane Katrina. But that is a costly and, many would say, doomed enterprise. Coastal cities around the world will likely have to be abandoned and relocated as the cost of saving lives and repairing infrastructure becomes too great. Even important port cities, like New Orleans on the banks of the mighty Mississippi will eventually become unliveable. And these abandoned cities will leave their marks in the sedimentary layers forming all the time, to be discovered like mythical Atlantises by divers of the far future.
The coastal cities with the best chances of being preserved for posterity are those built on parts of the Earth’s crust that are being pulled ever so slowly downwards by the movement of tectonic plates, such as London. Cities drowned and then buried in silty blankets will persist in a petrified form. The subways and sewage pipes will perhaps resemble the traces left by some giant burrowing creature, and the deep foundation piles of high-rises will linger as uncharacteristic stripes in the layers of a future cliff. Little will remain of cities built in deserts, such as Las Vegas and Lima, those built at altitude, such as La Paz, and those exposed to violent destruction from cyclones, volcanoes or earthquakes, like Kathmandu.
These seemingly permanent symbols of our species’ great civilisations are as vulnerable as we are to the ravages of time, and to humanity’s destructive practices. Our industrial pollution is impacting the man-made world as surely as it is affecting the natural world. Millions of years from now, there may be few signs of the mighty cities that have transformed our planet.