Global mean sea level is rising 25 percent faster now than it did during the late 20th century largely due to increased melting of the Greenland Ice Sheet, a new study shows. However, the researchers’ more accurate estimate of sea level rise was slightly lower than previous estimates.
The new study revisits how well these measurements agree with independently observed changes in the various components contributing to sea level rise, from the melting of glaciers to the amount of water vapor in the atmosphere. Using this approach, the new study finds the global mean sea level, or the average height of the world’s oceans, has been increasing by three millimeters (.1 inches) per year on average during the satellite period.
The research also finds the rate of global mean sea level rise increased by 0.8 millimeters (.03 inches) per year during the second half of the satellite period, from 2004 to 2015.
The new study is not the first to estimate sea level rise, but the comprehensive approach used by the authors provides perhaps the best estimate yet of how fast global mean sea level is changing, said Anny Cazenave, a space geodesist at the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS) in Toulouse, France, and co-author of the new study published in Geophysical Research Letters, a journal of the American Geophysical Union.
“We came up with new numbers and a new, more robust view of what is going on,” Cazenave said.
Global mean sea level is one of the best indicators of climate change, because it integrates many changes occurring in the climate system, from the melting of glaciers to the amount of water stored on land to the amount of water vapor in the atmosphere, Cazenave said.
The ocean is currently storing most of the additional heat generated by greenhouse gas warming, and because of the ocean’s slow response to this additional heat, sea levels will continue to rise for hundreds of years, even if emissions of greenhouse gases ceased immediately, Cazenave said. Because of this, accurate sea level rise information like that detailed in the new study will be needed to model future sea levels for centuries, she said.
“It is very important to accurately know how sea level is evolving, what is the current rate of sea level rise and if there have been changes in this rate of sea level rise during the last decade,” Cazenave said. “Now we have in hand a new number that seems to be robust and says, yes, global mean sea level is accelerating, and we can say this is because of accelerating land ice melt.”
The researchers analyzed information from 26 data sets to recalculate the sea level budget and come up with a new estimate of the global mean sea level rise rate. They were also able to account for drift from an instrument used to measure sea level in the 1990s that scientists had thought could be throwing off sea level rise estimates. Satellites first started measuring sea level rise in 1993.
Warming of the deep ocean currently has a negligible contribution to sea level rise, according to Cazenave.