International
A surface elevation table is used to measure subsidence in a tropical swamp in Indonesia. SIGIT DENI SASMITO/CIFOR/FLICKR

At many river deltas, scientists are missing a major source of sea level rise

For coastal communities, the sea level rise propelled by melting ice and warming oceans is bad enough. But people living on the soft, compressible sediments of river deltas have another factor to contend with: sinking land.

Scientists have traditionally inferred the sinking from tide gauge readings or measured it directly at GPS stations. But a team of scientists now says these methods significantly underestimate subsidence at many deltas and low-lying coastlines worldwide.

In recent years, scientists at Tulane University in New Orleans, Louisiana, have shown that in the Mississippi River delta, fluffy, young sediments within a few meters of the surface are compacting rapidly. They estimate the effect more than doubles the region's rate of sea-level rise to a total of 13 millimeters a year. Tide gauges and GPS stations miss that subsidence because they are anchored to deeper layers, which are less susceptible to compaction.

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