The impact of subsidence, the gradual caving in or sinking of an area of land, in coastal communities, along with sea-level rise has long been considered a local issue, at least until now.
A new study by researchers from the University of East Anglia, published March 8, 2021, in Nature Climate Change is the first to analyze global sea-level rise combined with measurements of sinking land.
According to the new study, residents in coastal communities are experiencing an average sea level rise of 7.8 mm – 9.9 mm (0.31 in – 0.39 in) per year over the past twenty years, compared with a global average rise of 2.6 mm (0.10 in) a year.
The impacts are far larger than the global numbers reported by the Intergovernmental Panel on Climate Change (IPCC), reports Eurekalert.
“We’ve actually quantified (sea level rise) and are able to get the relative magnitude. And it’s surprising — it’s surprisingly large. We’re making the point that climate change is bad and climate-induced sea-level rise is bad,” Robert Nicholls, lead author of this research and director of the U.K.’s Tyndall Centre for Climate Change Research, according to CTV News Canada.
The evidence is already obvious
It is not as if no one was aware of the sinking lands along coastal areas where humans have congregated. In a study published in the journal Science Advances on March 7, 2018, Manoochehr Shirzaei at Arizona State University and Roland Bürgmann at the University of California, Berkeley show that major portions of San Francisco Bay’s shoreline are sinking faster than the sea is rising.
Much of the infrastructure along the Bay’s shoreline was built on mud that compacts over time, lending some stability. This land is sinking at a rate of about 2.0 millimeters a year, about the thickness of a nickel. But other areas aren’t so lucky.
Areas like San Francisco International Airport, Treasure Island, and Foster City were built on fill that was not densely compacted – like sand, gravel, garbage, and other debris. These areas are sinking at a much faster rate, about 10 millimeters, or nearly half an inch a year.
In 2019, Indonesian President Joko Widodo announced plans to move the country’s capital away from Jakarta, reportedly the fastest sinking city in the world.
Located on the island of Java, the city is sinking at a rate of 10 inches a year due to a number of reasons, just one of them associated with climate change.
And in Nova Scotia, Canada, many communities are built close to the water, and the province has one of the most severe rates of sea-level rise in the country, according to CBC Canada.
This is because as the water rises, the land is sinking as a consequence of the last ice age. The area around Hudson Bay, which was depressed by the thickest part of the Laurentide Ice Sheet thousands of years ago, is now rebounding and moving upward.
Nova Scotia, which was at the thinnest part of the ice sheet, is going in the opposite direction. This strange phenomenon is known as glacial isostatic adjustment — and means the Maritimes are subsiding at a rate of about 15 centimeters per century.
Assessing four components of relative sea-level change
The research took into account four factors that impact changes in sea-level rise. They include climate-induced sea-level change, the effects of glacier weight removal causing land uplift or sinking, estimates of river delta subsidence and subsidence in cities.
Using the Dynamic Interactive Vulnerability Assessment (DIVA) model which is designed for understanding coastal management needs and Sea-level measurements from satellite data, the research team found that impacts and adaptation needs are much higher than reported global sea-level rise measurements suggest.
The research also shows high rates of relative sea-level rise are most urgent in South, South East, and East Asia as the area has many subsiding deltas and coastal flood plains, growing coastal megacities, and more than 70 percent of the world’s coastal population.
Perhaps the most important lesson we can take from this study is the need to aggressively manage our coastal communities, including stopping the withdrawal of groundwater that is increasing subsidence and better management of river deltas. This, along with doing better at mitigating the effects of climate change is necessary.
