Climate change is altering our world, and not for the better. The Intergovernmental Panel on Climate Change (IPCC) report published in September 2019 paints a picture of a world on the verge of crisis. Among the many climate-related challenges highlighted by the report, increased risk of flooding in coastal areas due to extreme weather events is drawing attention.
As many as 280 million people could be displaced by sea level rise and catastrophic superstorms, according to the IPCC report. Many of these are in major urban areas. More than two-thirds of the world’s megacities – those with populations of between eight and 10 million – are on the coasts.
“There are three really vulnerable populations at risk from sea level rise: small island nations, deltas and coastal cities,” says Ivan Haigh, Associate Professor of Oceanography at Bristol University. According to Haigh, regardless of any actions taken now to combat climate change, these populations will be impacted by sea level rise.
“Even if we were to go to negative emissions tomorrow, sea levels are still going to rise for hundreds of years,” Haigh says.
Despite the risks, these areas keep growing. A 2013 study by the World Bank put Jakarta and Miami atop the list of megacities with the most to lose, both economically and in terms of population risk. By 2050, Jakarta faces average annual losses of EUR 1.5 billion. If flood defences are breached, those losses could exceed EUR 9 billion every year.
“At the time of the study there were 139 coastal cities with a population of at least a million. In the 1960s there were only two megacities. It’s projected in 20 years there will be up to 50. So, it shows you the scale of the problem,” says Haigh.
These cities aren’t just major population centres. They’re also centres of commerce and manufacturing. Their economic importance is one reason nations are working to shore up defences.
“It’s likely certainly in the short term that we’re always going to try and defend our cities,” says Haigh. “London is the classic example. Without the Thames Barrier, there’s no city.”
There is a staggering amount of wealth protected by the movable flood barrier, which took eight years to build at a cost of EUR 618 million. It guards some 1.2 million houses and more than EUR 231 billion in property across 125 sq. km of the city.
Miami Beach, the economic centre of the Florida coastline, is only two metres above the current sea level. There, city politicians are spending EUR 1.8 million per city block to raise the roads by a little over half a metre. In New York, Mayor Bill de Blasio recently unveiled a EUR 9 billion plan to build seawalls 1.5-2 metres above sea level around the city at a cost of up to EUR 600 per metre.
Any solutions are going to be expensive, notes Kevin Horsburgh, chief scientist at the UK’s National Oceanography Centre in Liverpool. Horsburgh authored the UK Climate Projections series of advice for government and has advised the Office for Nuclear Regulation on long-term infrastructure issues.
“The sums of money are going to be vast, that goes without saying,” Horsburgh says. But, he notes, the costs of erecting barriers have to be considered next to the alternative. “You can’t just suddenly ask 10 or 20 million people to move. Compare that to the creation of a new city elsewhere. It’s just arithmetic: is it cheaper to adapt or move?”
Some cities, however, have come down on the other side of that equation.
Jakarta, the capital of Indonesia, sits on a river delta. Years of groundwater extraction – pumping water from deep wells for drinking water or to make concrete to support city expansion – has caused severe subsidence, resulting in the city starting to literally sink into the sea.
“The northern part of Jakarta is subsiding at a rate of up to 10 cm per year,” says Gilles Erkens, a geologist who chairs the Deltares Research Institute in the Dutch city of Utrecht. “There are streets in Jakarta near the harbour that flood twice a day, every day, because of the tide, says Horsburgh. They haven’t got a sea level problem, they’ve got a tide problem because the land has sunk. Compared with the UK, the population densities are also absolutely huge.”
The city has sunk by up to four metres since the 1960s.
In terms of measurements it’s often difficult to distinguish between subsidence and sea level rise. If there is human-induced subsidence in urban centres like Bangkok, Jakarta, or Shanghai, subsidence has a larger impact on people’s lives than sea level rise.
Additionally, sea level rise has to be addressed by tackling impact on climate on a global scale. Subsidence, on the other hand, is a local problem: If you want to tackle subsidence in Jakarta, you have to take action in Jakarta, there’s no need to do something in Japan or the Netherlands.
“On one hand it’s easier but on the other hand it’s more confronting, there’s nowhere to hide, it’s your own responsibility,” says Erkens.
The need and ability of individual cities to take local action led to Indonesian President Joko Widodo’s announcement that the capital will move to Borneo.
Moving cities will have serious economic implications for major maritime hubs, not least because the interconnectedness of cities makes it difficult to just pick up a city and drop it elsewhere.
Many coastal megacities grew up around ports, and remain tied to the shipping industry, which exposes them to further risk.
“If you’re growing your country’s blue economy of the basis of exports, then you will be building some kind of infrastructure, but the moment you do that, it has some threat from sea level rise,” says Horsburgh.
This doesn’t mean that there is no room for innovative solutions to be implemented, however. Automated dock-to-dock shipping can help reduce waiting time in terminals, and AI-controlled route planning could reduce overcapacity and slash waiting times at ports, cutting the amount of fuel that is burned as ships sit idle waiting to be unloaded.
The net effect of these changes could see fuel efficiency improve by between 5% and 7%, using many millions of tonnes fewer of liquified natural gas and diesel.
“I think many of the world’s cities, particularly in southeast Asia are going to face enormous challenges, and I think there will have to be some areas where they do retreat,” says Haigh.
Nevertheless, Haigh says there are reasons to be optimistic. “As a society we are incredible. There is nothing we can’t accomplish, and I think we have all the technology we need to adapt. The problem is that cities are not spending enough money on it.”
Erkens highlights two recent examples where megacities have implemented solutions to face off against this existential threat.
“The most inspiring solutions used to tackle subsidence are probably in Tokyo, and also in parts of Venice where they have stopped the deeper groundwater extraction,” he says. “And then they turned to other sources of water supply, for example treated service water, as well as programs to reduce water demands.
“Of course, the enormous investments that have to be done is what is holding back other cities from doing something similar. And particularly because you need very brave politicians to do this on a very large scale: it will only benefit you in the longer term, but you have to pay a lot of money up front.”