In addition to generating 8% of global carbon emissions, recent studies have
highlighted another negative impact of the world’s most popular building
material — its weight, which is causing a host of coastal cities to sink faster
than sea levels are rising.
Concrete
is the second most widely used substance on earth, next to water. It’s well
understood that concrete has an emissions
problem
— the concrete industry is responsible for 8 percent of all global carbon
emissions — however, the impact of its weight in sustainable development is less
discussed. Concrete demand is expected to
increase
48 percent by 2050, but humanity’s favorite building material is literally
causing the downfall of cities around the world.
Subsidence — the sinking or lowering of the earth’s surface — could
significantly impact nearly 20
percent of the
global population, especially as sea levels continue to rise. Subsidence is
caused by multiple factors, both natural- and human-caused. 2022
research by
the University of Rhode Island used five years of satellite data to measure
the subsidence rate of 99 coastal cities across the globe. The results: Coastal
cities are sinking under their weight faster than sea levels are rising.
“If subsidence continues at present rates, these cities will be challenged by
flooding much sooner than projected by sea-level-rise models,” the report reads.
“Expanded monitoring and policy interventions are required to reduce subsidence
rates and minimize their consequences.”
In most of the coastal cities evaluated, areas are subsiding at roughly 2mm per
year — faster than the normal subsidence of more stable regions. But in 33
cities, parts are sinking 10mm or more each year — five times faster than global
sea-level rise. The worst sinking is occurring in cities located in South,
Southeast and East Asia: In several Asian cities, subsidence rates
exceed 30mm per year — overshooting sea-level rise nearly fifteen-fold.
Many geological phenomena outside of human control play a pivotal role in
subsidence rates. But groundwater extraction, oil and gas production, and the
weight of the built environment are dominant factors causing many of the worst
subsidence rates in the world. While groundwater withdrawal for manufacturing
and urban centers is usually the biggest anthropogenic contributor to
subsidence, the weight of the built environment is undeniably making it worse in
some of the world’s biggest cities.
China’s record-breaking urban
expansion
over the past several decades created an unprecedented demand for concrete,
where the unimaginable weight of the country’s rapidly growing cities is causing
major population centers to
sink rapidly: Some
portions of Beijing are sinking over 40mm each year.
But Beijing is not alone: A Chinese
study published last
month in the journal, Science, found that 40 percent of the landmass in 82 large
Chinese cities exhibits moderate to severe sinking — exacerbating the effects of
sea-level rise and flooding events for millions of people.
“By 2120, 22 to 26 percent of China’s coastal lands will have a relative
elevation lower than sea level, hosting 9 to 11 percent of the coastal
population, because of the combined effect of city subsidence and sea-level
rise,” the report reads. “Our results underscore the necessity of enhancing
protective measures to mitigate potential damages from subsidence.”
A 2023 study
published in the journal, Earth’s
Future, found a
similar thing happening in New York City. Like many cities across the world,
New York’s broader subsidence rate is thought to be hastened by factors
including glacial retreat and groundwater extraction. While building load alone
isn’t the only factor causing the world’s cities to sink, heavy buildings and
infrastructure can greatly exacerbate the natural subsidence rate of an area —
especially when constructed on soft or previously excavated ground like that
beneath parts of Manhattan.
“[E]very additional high-rise building constructed at coastal, river or
lakefront settings could contribute to future flood risk, and mitigation
strategies may need to be included,” wrote the authors of the New York study.
“Major cities on every continent except Antarctica are observed to be
subsiding … and the issue may be worsened as populations grow. Increasing
urbanization will likely exacerbate subsidence by groundwater extraction and/or
construction density — which, combined with accelerating sea-level rise, implies
a growing flood hazard in coastal cities. As these trends continue, it will be
important to be mindful of accompanying mitigation strategies against inundation
in growing coastal cities.”
As the Rhode Island authors warn: “Even in developed countries of North
America, Europe and Australia, parts of many cities appear to be
sinking faster than sea level is rising. [C]ities and nations that fail to
address the cause(s) of their subsidence will be challenged by flooding much
sooner than projected by sea-level rise models. … Continuous monitoring and
policy intervention are required to reduce subsidence rates and minimize their
consequences.”
Many low-carbon material-science startups are creating ways to reduce concrete’s
climate impacts — finding solutions in
biomimicry
and alternative materials such as captured
carbon.
One company, Eco Material Technologies, utilizes
waste fly ash to produce low-carbon alternatives for the Portland cement found
in concrete. But low-carbon concrete doesn’t necessarily mean less weight.
"Eco Material’s products greatly improve the durability and sustainability of
concrete, but they do nothing for reducing its weight,” the company told
Sustainable Brands® in an email.
Potentially, a combination of low-carbon concrete that’s more durable than
legacy concrete — coupled with smarter design to utilize less of the material —
could mitigate some of the adverse global effects of concrete production and
use. But weight is still a looming issue that will need to be addressed for
coastal cities to adapt to the effects of climate change.
Published May 16, 2024 8am EDT / 5am PDT / 1pm BST / 2pm CEST
Christian is a writer, photographer, filmmaker, and outdoor junkie obsessed with the intersectionality between people and planet. He partners with brands and organizations with social and environmental impact at their core, assisting them in telling stories that change the world.
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