Report warns of ‘clear trend’ of accelerating sea level rise
Gulf Coast increases at twice the global average
The rate of sea level rise along much of the U.S. coastline continues to accelerate, according to a new report.
The report’s key message “is a clear trend toward acceleration in rates of sea-level rise at 25 of our 32 tide-gauge stations,” Virginia Institute of Marine Science professor emeritus John Boon said in a statement. “Acceleration can be a game changer in terms of impacts and planning, so we really need to pay heed to these patterns.”
Boon and other researchers at William & Mary’s Virginia Institute of Marine Science released the report Monday.
Sea level rise acceleration was highest along the Gulf Coast, where Grand Island, Louisiana, saw a nearly 8 millimeter yearly increase, double the global average, according to the report. Galveston and Rockport in Texas also had significant increases.
The report includes 51 years of water level observations, from January 1969 through December 2019.
Worldwide, sea level has risen about 8 inches since 1880 but, unlike water in a bathtub, it doesn’t rise evenly. In the past 100 years, it has climbed about a foot or more in some U.S. cities because of ocean currents and land subsidence.
Here’s why: As the planet air warms, so do the seas. Heat-trapping greenhouse gases cause more land ice (glaciers and ice sheets) to melt and water to expand. Warmer water simply takes up more room than cooler water.
Scientists say global warming will be the primary cause of rising sea levels in the future. Their greatest uncertainty is how quickly the massive West Antarctic ice sheet will melt.
The current acceleration began around 2013 or 2014, the report says, likely associated with ocean dynamics and ice sheet loss. In 2019, rates of sea level rise accelerated at all 21 of the stations studied along the U.S. East and Gulf coasts and at seven of the eight monitored stations along the U.S. West
Coast.
“Although sea level has been rising very slowly along the West Coast, models have been predicting that it will start to rise faster,” the marine science institute’s Molly Mitchell said.
In Alaska, all four stations monitored show relative sea level falling at increasingly rapid rates because of coastal mountain-building, the report said.
The National Oceanic and Atmospheric Administration also has warned about sea level rise acceleration. It has noted that by the end of the century, global sea level is likely to rise at least one foot above 2000 levels, even if greenhouse gas emissions follow a relatively low pathway in coming decades.
“On future pathways with the highest greenhouse gas emissions, sea level rise could be as high as 8.2 feet above 2000 levels by 2100,” NOAA warned.
Mitchell said that “seeing acceleration at so many of our stations suggests that – when we look at the multiple sea level scenarios that NOAA puts out based on global models – we may be moving toward the higher projections.”