By Darien Kaufman in Mashable, 26 June 2017
A new study, published in June in the journal Nature Climate Change, confirms an acceleration in sea level rise during the past few decades. There had been greater uncertainty about this before, with climate deniers latching onto that and arguing that such an acceleration has not, in fact, been occurring.
However, by using calculations of the various contributing factors to sea level rise, such as melting ice sheets, water expansion that occurs as the oceans warm, and other factors, researchers from institutions in China, Australia, and the U.S. found that global mean sea level increased from about 2.2 millimeters per year in 1993 to 3.3 millimeters per year in 2014.
While that may seem tiny, the numbers add up quickly. These rate changes are the difference between a decadal sea level rise rate of 0.86 inches and 1.29 inches, with greater acceleration expected in the future.
The findings also made clear how major contributors to sea level rise have been changing over time. And it doesn’t paint a pretty picture.
Whereas global ice mass loss constituted 50 percent of sea level rise in 1993, this rose to 70 percent in 2014. The study found that the largest increase came from the Greenland Ice Sheet, which made up just 5 percent of the global mean sea level rise rate in 1993, and now constitutes 25 percent of it.
Given scientists’ concerns about Antarctica’s stability, look for melting glaciers to comprise an even greater share of the sea level rise budget in the near future.
A different study published in early June found the rate of sea level rise just about tripled between 1990 and 2012.
A study published in 2016 found that if global warming continues above 2 degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels through 2100, then sea levels would end up rising faster than at any time during human civilization. That study found that in a warming scenario of 5 degrees Celsius, or 9 degrees Fahrenheit, which is roughly the path we’re on now, New York City could see more than a meter, or about 3.6 feet, of sea level rise with an even higher upper limit. This would make a Hurricane Sandy-sized storm surge far more common in the city.
A separate study published in February found that current rates of sea level rise are likely unprecedented in at least the past 2,800 years.
This week’s findings are in line with NASA’s estimate for the current rate of sea level rise, which is 3.4 millimeters per year.
The significance of the new study is that it resolves lingering uncertainties about mismatches between what scientists know about contributors to sea level rise, and measured rates from satellites. This study, along with other recent work, shows the two match up closely, and it nails down the sea level rise acceleration.
Also, the new research shows that coastal communities that are already struggling with increased flooding on an annual basis, such as Miami Beach, will have to cope with a rapidly worsening situation in coming decades.
For every millimeter that the local sea level rises, the easier it becomes for the ocean to hit previously unheard of flood levels. Storm surges ride on top of background sea levels, and like a basketball player playing on a court with a steadily rising floor, even weaker storms are becoming more likely to score a slam dunk.