Record-breaking sea-level rise found along U.S. coasts

A recent study spearheaded by researchers from Tulane University has revealed that sea levels along the United States’ Southeast and Gulf coasts have experienced rapid acceleration, breaking records over the past 12 years. 

The study, published in the journal Nature Communications, highlights an alarming increase in the rate of sea-level rise, with researchers detecting a half-inch per year increase since 2010. The scientists attribute this acceleration to the combined impact of man-made climate change and natural climate variability.

Study lead author Professor Sönke Dangendorf emphasized the seriousness of these findings: “These rapid rates are unprecedented over at least the 20th century and they have been three times higher than the global average over the same period.”

To better understand the factors contributing to this acceleration, the researchers analyzed a combination of field and satellite measurements dating back to 1900. Study o-author Noah Hendricks, an undergraduate student in Dangendorf’s team at Old Dominion University, explains that they “systematically investigated the different causes, such as vertical land motion, ice-mass loss, and air pressure, but none of them could sufficiently explain the recent rate.” 

Instead, the researchers discovered that the acceleration is a widespread signal spanning from the Gulf of Mexico’s coasts to Cape Hatteras in North Carolina, the North Atlantic Ocean, and the Caribbean Seas. This pattern indicates changes in the ocean’s density and circulation.

According to the scientists, the primary factors driving the expansion of this area, known as the Subtropical Gyre, are shifting wind patterns and ongoing warming. Warmer water masses require more space, contributing to the rise in sea levels. 

The study suggests that the recent acceleration is an unfortunate combination of man-made climate change signals and a peak in weather-related variability that persisted for several years. The researchers expect that the rates will likely return to more moderate values as predicted by climate models in the coming decades.

However, study co-author Professor Torbjörn Törnqvist warns that this should not be mistaken for an all-clear signal: “These high rates of sea-level rise have put even more stress on these vulnerable coastlines, particularly in Louisiana and Texas where the land is also sinking rapidly.” 

Dangendorf adds that the “results, once again, demonstrate the urgency of the climate crisis for the Gulf region. We need interdisciplinary and collaborative efforts to sustainably face these challenges.”

The study was conducted with the collaboration of several experts from various institutions, including Qiang Sun from Tulane, John Klinck and Tal Ezer from Old Dominion University, Thomas Frederikse from the Jet Propulsion Laboratory in Pasadena, California, Francisco M. Calafat from the National Oceanography Centre in Liverpool, UK, and Thomas Wahl from the University of Central Florida in Orlando.

Future sea-level rise

Predictions for future sea-level rise vary depending on the emission scenarios, climate models, and timeframes considered. According to the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (2021), global mean sea level is projected to continue rising over the 21st century, with different rates depending on the greenhouse gas emission scenarios.

Under a low-emission scenario (SSP1-1.9), the report estimates a global mean sea-level rise of 0.28 to 0.55 meters (11 to 22 inches) by 2100 compared to the 1995-2014 average. 

In a moderate-emission scenario (SSP2-4.5), the projected rise ranges from 0.34 to 0.65 meters (13 to 26 inches). However, under a high-emission scenario (SSP5-8.5), sea levels could rise between 0.63 and 1.02 meters (25 to 40 inches).

These estimates account for multiple factors contributing to sea-level rise, including thermal expansion of ocean waters, melting glaciers, and the loss of ice from Greenland and Antarctic ice sheets. It is important to note that regional variations in sea-level rise will occur due to factors such as ocean currents, land subsidence, and changes in Earth’s gravitational field.

Predictions beyond 2100 remain uncertain, but under most scenarios, sea-level rise is expected to continue for centuries. The magnitude of long-term sea-level rise will depend on future greenhouse gas emissions and the Earth’s climate system’s response. Reducing emissions and implementing adaptation measures are critical to mitigating the impacts of sea-level rise on coastal communities, infrastructure, and ecosystems.

Worst-case scenario for sea-level rise

Under the worst-case scenario, where sea levels rise by 40 inches (1.02 meters) by the year 2100, the consequences would be profound and widespread, particularly for coastal regions and low-lying areas. Some of the potential impacts include:

1. Coastal flooding: The frequency and severity of coastal flooding would significantly increase, affecting millions of people living in coastal areas. Some regions would experience more frequent and devastating storm surges and extreme weather events, potentially resulting in loss of life and property.
2. Loss of land and property: As sea levels rise, low-lying coastal areas would be permanently submerged, leading to the loss of valuable land and property. Many major coastal cities and communities would be at risk, forcing people to relocate.
3. Displacement of populations: The loss of habitable land would lead to the displacement of millions of people worldwide, creating a massive wave of climate refugees. This could result in social, economic, and political challenges as nations struggle to accommodate the influx of displaced populations.
4. Infrastructure damage: Vital infrastructure such as roads, bridges, ports, airports, power plants, and sewage treatment facilities in low-lying coastal areas would be at risk of flooding and permanent inundation. The costs of repairing or relocating this infrastructure would be immense.
5. Economic impacts: The loss of land, infrastructure, and property would have significant economic consequences. Tourism, agriculture, and fisheries in coastal areas would be severely affected. In addition, the costs of adaptation measures and disaster response would place a heavy burden on governments and taxpayers.
6. Ecosystem disruption: Rising sea levels would lead to the loss of coastal ecosystems, including wetlands, mangroves, and coral reefs, which provide essential habitats for numerous species and act as natural barriers against coastal erosion and flooding. The loss of these ecosystems would have cascading effects on biodiversity, fisheries, and the overall health of the oceans.
7. Saltwater intrusion: As sea levels rise, saltwater would infiltrate into coastal freshwater resources, contaminating drinking water supplies and agricultural lands. This would exacerbate water scarcity issues and negatively impact agriculture and food security in affected regions.
8. Cultural heritage loss: Many historically and culturally significant sites located in coastal areas would be at risk of being lost or damaged due to rising sea levels and increased coastal erosion.

To mitigate these potential consequences, it is crucial to reduce greenhouse gas emissions, implement effective adaptation measures, and improve the resilience of coastal communities and infrastructure to the impacts of sea-level rise.

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