Ocean levels on Earth have risen an average of three inches in the last 23 years, and could rise an additional three feet in the next century, according to an interdisciplinary NASA team charged with measuring changing sea levels.
Scientists from NASA Wednesday presented satellite data gathered since 1992 that measured ocean levels rising at an average of 3 millimeters per year. The findings pointed to thermal expansion caused by warming ocean temperatures, as well as melting ice sheets and glaciers, as the reasons for the rise — and scientists warned that the rate at which sea levels are climbing is accelerating.
“Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it’s pretty certain we are locked into at least 3 feet of sea level rise, and probably more,” Steve Nerem, a professor at the University of Colorado Boulder and leader of NASA’s Sea Level Change Team, told reporters in a Wednesday afternoon conference call. “But we don't know whether it will happen within a century or somewhat longer.”
The United Nations Intergovernmental Panel on Climate Change made a comprehensive assessment of rising sea levels in 2013, with climate experts stating that oceans would rise from one to three feet by the end of the century.
But NASA said Wednesday that satellite data gathered since then has shown that sea levels will climb to the higher end of that range, though it will be difficult to predict exactly how long it will take to reach that level.
Along with partners from French space agency Centre National d'Études Spatiales, the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and the U.S. National Oceanic and Atmospheric Administration (NOAA), NASA has been tracking changing sea levels and the melting of ice sheets and glaciers using satellites equipped with highly sensitive instruments.
Mike Freilich, director of NASA’s earth science division in Washington, explained that the satellites were so accurate that they would be able to detect the movement of a dime lying on the ground from 40,000 feet above it.
The scientists said that melting ice sheets in Greenland and Antarctica have been contributing to rising sea levels sooner and more significantly than they had anticipated.
“On a personal level,” said Eric Rignot, a glaciologist at the University of California – Irvine and NASA’s Jet Propulsion Laboratory in Pasadena, “the data collected over the last few years make me more concerned about the melting of the ice sheets than I was before.”
Sea levels don’t rise uniformly across the planet, and in some places — particularly on the West coast of the U.S. — they are actually declining due to natural cycles of ocean currents. The scientists expect sea levels in those regions to catch up, and perhaps to exceed global average sea levels.
“People need to understand that the planet is not only changing, it’s changed,” said NASA scientist Tom Wagner during the conference call.
“If you’re going to put in major infrastructure like a water treatment plant or a power plant in a coastal zone ... we have data you can now use to estimate what the impacts are going to be in the next 100 years,” Wagner said.
“Sea level rise will measurably change the shape of our coastline, especially in low-lying states like Florida,” added NASA’s Freilich.
Researchers noted that with the Greenland and Antarctic ice sheets melting, it will be difficult for scientists to predict when sea levels will rise as a result because they have never actually witnessed the collapse of an ice sheet.
“This is a continuing and evolving story,” said Rignot. “We’ve never seen something like this on this scale before.”
With wire services