When you hear of global cities most at risk of being inundated by rising seas, it's usually a pretty standard list: New York City, Boston, Miami Beach, Venice, New Orleans, Rio De Janeiro and a whole swath of the waterlogged but soberly prepared Netherlands usually make the cut.
And there is good indeed a reason to worry — and take action — in each of these vulnerable cities. But a new briefing paper published by London-based charity Christian Aid finds coastal cities that are already actively sinking are even at greater peril of being impacted by climate change-fueled sea level rise.
Spanning four continents, eight of the most high-risk sinking cities identified by Christian Aid — London, Shanghai, Bangkok, Houston, Jakarta, Manila, the Bangladeshi capital of Dhaka and the Nigerian city of Lagos — are collectively home to over 83 million people. This number is sure to grow exponentially as global urban centers continue to burst from their seams. Per the report, 59 percent of the world's population will live in cities by 2030. Asia has experienced — and will continue to experience — the most rapid urban growth. Currently, 54 percent of the Asian population resides in low-lying, storm-prone coastal areas.
Titled "Sinking Cities, Rising Seas" the paper was published just ahead of the United Nations' Intergovernmental Panel on Climate Change (IPCC)'s landmark special report detailing how the world must work together to limit the rise in global temperatures to 1.5 degrees Celsius above pre-industrial levels in order to stave off certain climate catastrophe. (The short and only solution: the immediate and aggressive reduction of greenhouse gas emissions with unprecedented global coordination.) If not limited, sea levels could rise as much as 40 centimeters — nearly 16 inches — in the coming decades. And as Christian Aid explains, a 2 degree Celsius rise in global warming "would take us into a climate regime unparalleled in human history."
Writes Dr. Katherine Kramer, Christian Aid's global lead for climate change and lead author of "Sinking Cities, Rising Seas:"
Even with the current 1 degree Celsius of warming climate, vulnerabilities to climate impacts are becoming increasingly obvious — as in this year's northern hemispheric heat wave and the lethally catastrophic storms Mangkhut and Florence demonstrate.
Collective, collaborative and unprecedented efforts to limit warming by reducing greenhouse gas emissions as quickly and deeply as possible, in line with limiting warming to 1.5 degrees Celsius with a high probability is essential to reduce this climate vulnerability. This will require the world to achieve net zero emissions5 by 2050.
Kramer goes on to explain that the eight global cities used as case studies in the report all have heightened "overall vulnerability to sea level rise and to damaging storm surges" due to the fact that they're, well, sinking into the earth. Some cities, such as Jakarta, have lost their valuable natural means of flood protection to rampant development. Additional factors like poor planning exacerbate an already dire situation while "climate change acts as a further multiplier of existing and future vulnerabilities."
"These global metropolises may look strong and stable, but it is a mirage," Kramer tells The Guardian. "As sea levels rise, they are increasingly under threat and under water."
Here's a look at the eight cities spotlighted in "Sinking Cities, Rising Seas" with info on why they're sinking, what's at stake and how they've taken action if at all.
Sprawling, low-lying Houston was ravaged by flooding unleashed by deadly rain-marker Hurricane Harvey in 2017. (Photo: Revolution Messaging/Flickr)
Situated on the banks of the Buffalo Bayou and its tributaries, pancake-flat Houston — Texas's biggest city and the fourth most populous city in the United States — is sinking just as fast as the sea is rising. Just barely squeaking above sea level, Houston's topography is naturally precarious. But human activities such as industrial-scale groundwater extraction and, most notably, oil and gas production have only caused this vibrant and diverse Texas metropolis to sink and sag — a phenomenon known as subsidence — even further.
"Ironically, being a fossil producer is undermining Houston's already-limited resilience to climate impacts, including sea level rise," writes Kramer.
In total, the Houston-Galveston region has sunk a total of 105.9 inches over the decades. Currently, northwestern sections of the city are sinking that fastest at a rate of roughly 2 inches per year. Houston, we really do have a problem.
In Jakarta, extensive groundwater extraction and a dense, vertical skyline make for a particularly perilous pair. (Photo: Ya, saya inBaliTimur/Flickr)
The Indonesian capital of Jakarta holds the dubious distinction as the fastest sinking city in the world at a clip of roughly 10 inches per year. About 40 percent of the sprawling city now lies below sea level per the report.
The main reason this city of nearly 10 million is sinking — and sinking so fast — is relatively straightforward: the absence of a reliable network of piped-in water has led to a preponderance of illegal private wells used by Jakarta residents to extract groundwater. And it's these wells that have drained underground aquifers and prompted such dramatic subsidence ... "like deflating a giant cushion underneath it [the city]," wrote The New York Times of Jakarta's "surreally fast" descent in 2017. "Rivers sometimes flow upstream, ordinary rains regularly swamp neighborhoods and buildings slowly disappear underground, swallowed by the earth."
And that's not the only issue. Jakarta's soaring skyline packed-full of hulking, high-rise buildings is further squashing the city. "While the loss of groundwater undermines Jakarta from underneath, the sheer weight of its buildings pushes from above, causing further sinking," writes Christian Aid.
Bangkok is another Asian metropolis that's wealth of high-rise buildings isn't doing it any favors in the subsidence department. (Photo: Stephanie Kraus/Flickr)
With an elevation that reaches just five feet above sea level, governmental officials estimated in 2015 that the Thai capital, which is sinking at a little under an inch per year, could be submerged within 15 years if the water around the city doesn't cease rising at the current rate.
While subsidence caused by groundwater extraction is less an issue than it once was in Bangkok, the ground beneath the city is essentially caving in under the substantial heft of its cloud-brushing built environment. "As elsewhere, Bangkok's sinking feeling has ironically been made worse by its reaching for the skies. The sheer weight of its buildings are pressing into the riparian sediments and compacting them as the sustaining water is depleted from them," writes Christian Aid.
Per Thailand's National Reform Council, which recommends building a massive seawall around the city, there are more than 700 building with more than 20 floors spread out across Bangkok and more than 4,000 buildings with between eight and 20 stories.
London's Thames flood defenses are used six to seven times per year — double the amount anticipated when the barriers were first completed. (Photo: Jack Torcello/Flickr)
Tapped-out aquifers and far too many heavy skyscrapers aren't necessarily to blame for the fact that the British capital city is gradually sinking. From a geological perspective, it's actually largely Scotland's doing.
Kramer explains how a phenomenon known as glacial isostatic adjustment — a "vestige of the last ice age" — is responsible for already flood-prone London's slow descent downwards. The sinking "is a result of the weight of the glaciers pressing down on Scotland 11,000 years ago. These depressed the north and allowed the south of the U.K. to relatively soar. However, since the UK's glaciers have melted, Scotland is on the rebound, at a rate of around 1mm [.04 inches] per year, and the south of the country is simply sinking back into the rising sea."
And one needn't look much further than London's primary flood defense, the Thames Barrier, to understand the how grim the situation is. Built and designed in 1984 to protect London from 1-in-100-year flood levels up to 2300, engineers anticipated that the barrier would be used two or three times annually. In actually, it's seen far more action and is currently used six to seven times per year.
Like many other sinking cities that are particularly vulnerable to the effects of climate change, Shanghai, the world's most populous city, is sinking under the weight of its own development. This has been made worse by groundwater extraction. Per the report, the total losses resulting from the structural havoc that subsidence has wreaked on Shanghai's buildings and infrastructure was roughly $2 billion from 2001 through 2010.
Shanghai, however, has demonstrated that aggressive schemes to slow subsidence have proven effective. Restrictions on private wells, a GPS system to better monitor the sinking and a larger shift away from groundwater extraction have helped to slow the city's annual sinking rate from 3.5 inches to less than half an inch.
What's more, an effort to pump billions of gallons of water into once tapped-out aquifers hasn't just slowed but even reversed sinking in some areas.
The Philippine capital of Manila is chaotic, vibrant and impossibly dense. It's also a verified fast-sinker at roughly 4 inches per year — that's 10 times the rate of sea level rise caused by global warming.
As Kramer explains, groundwater extraction is again the main culprit here: "Since the city has an average elevation of around 5 meters [16 feet], it seems to be living on borrowed time. The subsidence not only increases the absolute risk of flood, but also the areas affected: high tides can penetrate further inland and floods may recede more slowly. This means that there is increased risk of salination of soils that were previously fertile."
Water-intensive rice production just north of the city and illegal, flood-causing expansion of agricultural fishponds aren't helping matters.
With a rapidly growing population now topping 21 million people, the Nigerian port city of Lagos — the most populous city on the African continent — is especially vulnerable to rising seas due in part to a lack of adequate drainage systems and subsidence caused by groundwater extraction.
As Kramer writes, "some estimates suggest that a sea level rise of 20cm [7.8 inches] could cause 740,000 people to lose their homes across Nigeria: clearly the need to limit warming as much as possible is of paramount importance to avoid these people being internally displaced.
As the report details, the building of a new artificial island named Eko Altantic that's planned across from mainland Lagos is being touted as a potential economic boon that would generate new jobs, boost tourism and be an all-around great asset to the city on numerous fronts. However, many worry that the new island, which would be protected by a massive seawall, could have a detrimental impact on the surrounding islands during storm events by pushing storm surge onto them. "Non-sustainable development, combined with climate impacts, may not prove a good combination for the city," concludes Kramer.
Described as "another low-lying, river-side city beset by a sinking feeling caused by unsustainable extraction of groundwater," the Bangladeshi capital city of Dhaka is sinking at a rate of a little over a half-inch per year. (Shifting tectonic plates also play a hand in the subsidence experienced in the region although groundwater extraction is the primary cause.)
Although Dhaka's sink rate isn't as alarmingly fast as in some other cities, the overall situation is made exponentially worse by the fact that sea level rise in the Bay of Bengal is 10 times the global average. This has caused millions of people in low-lying coastal areas southwest of the city to migrate en masse to Dhaka's already overstuffed slums.
To their credit, city officials have undertaken some efforts to lessen the deadly impact of flood-producing weather events.