A new study reveals that the rise in global sea level from the end of the 20th century until the last two decades is accelerating significantly faster than what scientists previously thought. This has something to do with loopholes in the estimates made for an earlier period.
For a new study published in the journal Nature on Jan. 14, Carling Hay from Harvard's Department of Earth and Planetary Sciences (EPS) and colleagues reported that the global sea level rise in the 20th century was not quite as much as previously estimated.
Although prior research suggested that the sea had risen about six inches over the 20th century, the researchers found that the rise in sea level during this period was only by about five inches.
Since estimates made in the 1990s were accurate, it means that the rate of sea level rise over the past several decades has been higher than previously believed.
Before the 1990s, when satellites were not yet used, estimates in the rise in sea level depended on the records of tide gauges, which are unevenly distributed globally. From these records, researchers have estimated that the rise in sea level for the 20th century is at 1.6 to 1.9 millimeters annually. Unfortunately, this method has its limitations.
"But these simple averages aren't representative of a true global mean value," Hay said. "Tide gauges are located along coasts, therefore, large areas of the ocean aren't being included in these estimates. And the records that do exist commonly have large gaps."
Since satellites have been used over the past couple of decades, more accurate measurements have been taken, and the rate in global sea level rise is revealed to be approximately 3 millimeters per year.
"Our estimates from 1993 to 2010 agree with [the prior] estimates from modern tide gauges and satellite altimetry, within the bounds of uncertainty. But that means that the acceleration into the last two decades is far worse than previously thought," said Hay.
The researchers said that the rate of sea level rises is about 25 percent higher compared with previous estimates, and the accelerated rate can be blamed on the melting of the ice sheets in West Antarctica and Greenland, as well as the shrinking of the glaciers, phenomena that can be attributed to manmade global warming.
The researchers said that once the result of their study is validated, it could solve some discrepancies in estimates of global sea level rise.