If global temperatures rise above 1.5° Celsius above pre-industrial levels—the ideal temperature limit set by the Paris agreement—global sea levels will rise by more than 40 centimeters (approximately 15.7 inches) by 2100. If temperatures top 2° Celsius, sea level rise will be more than 50 centimeters (approximately 20 inches) by century’s end. This could be devastating to coastal cities around the world that are already vulnerable to storms and flooding because of geological or urban planning factors.
That is the finding of a report from Christian Aid looking at eight coastal cities especially vulnerable to the effects of climate change. The Christian Aid report is one of several from organizations around the world being published in anticipation of the Intergovernmental Panel on Climate Change (IPCC) report on how and if the world can achieve the 1.5° Celsius goal, The Guardian reported. The IPCC report, scheduled to be released on Monday, is expected to say that the 1.5° goal is possible with urgent action to reduce greenhouse gas emissions. The Christian Aid report helps illuminate what is at stake.
“These global metropolises may look strong and stable, but it is a mirage. As sea levels rise, they are increasingly under threat and under water,” report author Kat Kramer told The Guardian.
Jakarta, Indonesia: At a rate of 25.4 centimeters (approximately 10 inches) per year, Jakarta is the world’s fastest sinking city. Much of this sinking is due to the digging of illegal wells to access groundwater, since surface drinking water options are too polluted to be safe. Because more than 97 percent of the city is covered in concrete, the groundwater is not replenished by rain and rivers. The city is also sinking due to the weight of its buildings. In addition, natural flood barriers like mangroves have been cut down to clear space for housing.
Bangkok, Thailand: Bangkok faces a similar problem of skyscrapers pushing down on water-depleted soils. A study released by the city government in 2015 predicted it could be underwater within 15 years. Bangkok has taken some action to preserve groundwater, such as the Ground Water Act of 1977 that restricted the amount of groundwater extracted. The city is now sinking at a slower rate than before, and water is being pumped back into the ground, but it is not enough to save the city from rising seas.
Lagos, Nigeria: Lagos is built on the coast and incorporates a series of islands. Poor drainage worsened the impact of devastating floods in 2011, and some estimates say that just 20 centimeters (approximately 8 inches) of sea level rise could render 740,000 people across Nigeria homeless. Lagos also faces the problem of excessive groundwater extraction. In addition, authorities are planning the construction of a new island called Eko Atlantic, planned as a new capital and financial center and designed to be protected by a sea wall. There are concerns the new development could worsen flooding for the rest of coastal and island Lagos by pushing flood waters its way.
Manila, Philippines: Manila is also sinking due to groundwater extraction at a rate of 10 centimeters (approximately 4 inches) per year, 10 times the rate of climate-caused sea level rise. Another problem is its extensive rice fields, which consume more water than other crops and increase flood risk when illegal fish ponds are built in tidal channels.
Dhaka, Bangladesh: Dhaka is sinking at a rate of 1.4 centimeters (approximately 0.55 inches) per year, and sea level rise in the Bay of Bengal is apparently around 10 times the global average. About 1.5 million people have already migrated from coastal villages to the city’s slums. Dhaka’s woes are made worse by groundwater extraction. The fact that the Indian plate and Burman sub-plate are moving in a way that causes Dhaka to subside adds to its woes, though groundwater extraction plays a larger role in its sinking than plate tectonics.
Shanghai, China: Shanghai is another major city sinking under the weight of its own development as groundwater extraction and increased building cause it to subside. It is also losing sediment that would naturally protect it because its rivers are dammed or because it is used for building materials. Shanghai did work to take action against sinking by requiring official permits for wells from 1995 and sourcing more water from the river, and it has reduced its sinking from nine centimeters (approximately 3.5 inches) to one centimeter (approximately 0.4 inches) per year. It has also caused land to rise in some places by pumping water back into the ground. The report pointed out that in some places land had risen by 11 centimeters (approximately 4.3 inches), which is the difference between the sea level rise predicted for 1.5 and two degrees of warming.
London, England: During the last ice age, glaciers pressed down on Scotland, causing the south of UK land mass to rise. Now that the glaciers have melted, Scotland is rising at a rate of 1 millimeter (approximately 0.04 inches) per year, and the south of England, including London, is sinking. The Thames Barrier, opened in 1984 to protect London from a one-in-100-year flood, was expected to be used two to three times a year. It is currently used double that, six to seven times yearly.
Houston, Texas: Houston sits on the Buffalo Bayou and is naturally flood prone for that reason, but it also is sinking due to groundwater extraction and, ironically, from the extraction of oil and natural gas from the ground beneath it. The Houston-Galveston area has already lowered by three cubic meters (approximately 105.9 inches), and the northwest is sinking by two inches a year.