How Rising Seas Push Coastal Systems Beyond Tipping Points

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A new multidisciplinary case study from USGS and collaborators looks at how even modest sea-level rise threatens coastal communities, infrastructure and ecosystems such as beaches, tidal marshes and estuaries by pushing them past “tipping points,” the crucial junctures at which even slight changes can fundamentally alter how an entire system behaves.

A four-panel diagram shows how different amounts of sea-level rise change a coastal system.

Conceptual diagram of the tipping points in the Santa Barbara coastal system with increasing sea level rise. From top to bottom:
A) Present day: coastal habitats and infrastructure vulnerable.
B) 0.5 meter sea level rise (SLR): sandy beach ecosystems squeezed by SLR and urban infrastructure, tidal marsh habitats degrading.
C) 1 meter SLR: sandy beach ecosystems and salt marsh habitats almost completely eliminated, daily tidal flooding impacts urban environments.
​​​​​​​D) 2 meter SLR: Habitats lost, and urban environment highly susceptible to daily and periodic storm impacts. 

(Credit: USGS. Public domain.)

Above: A USGS researcher measures dune elevation at a sandy beach in southern California.

A new  study—published in the journal Nature--Scientific Reports by  the USGS Pacific Coastal and Marine Science Center and collaborators—looks at how even modest sea-level rise threatens coastal communities, infrastructure and ecosystems by pushing them past their “tipping points,” the crucial junctures at which even slight changes can fundamentally alter how an entire system behaves.  

In one example, the study projects that with just  10 inches  of sea-level rise in Santa Barbara, California, the resulting habitat loss from beaches and wetlands would degrade overall biodiversity and ecosystem function. 

“The Earth’s physical and biological systems are inextricably linked, but individual components will respond to [the effects of climate change] at different rates and reach critical ‘tipping points’ at different times,” said Patrick Barnard, USGS Research Geologist and a lead author of the study. 

Sandy beach ecosystems are particularly vulnerable to sea-level rise, the study notes, and may have already exceeded a tipping point in Southern California: As beaches decrease in height and width with rising seas, the already narrow intertidal zones—supporting invertebrates that help cycle nutrients by breaking down organic matter—shrink further. The upper portion of these beaches, where native coastal vegetation traps sand and builds dunes that can weather climate-fueled storm surges, also disappear with rising seas. 

By assessing  how different coastal environments respond to the effects of climate change, the researchers demonstrated that degradation of habitats along beaches and in tidal wetlands occurs much sooner and at lower sea-level rise than the more pronounced flooding of the adjoining communities. 

The study suggests that natural systems reach tipping points at much lower levels of sea-level rise than human-built systems, suggesting that significant ecosystem disruption can occur even as coastal communities and infrastructure remain relatively unaffected as sea levels rise. 

Local officials, land managers and other decision makers  can use the information in this study to inform  coastal habitat restoration and other mitigation measures.

Read the article, published in Nature--Scientific Reports, titled “Multiple climate change-driven tipping points for coastal systems.”

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