Last updated February 13, 2018 at 4:09 pm
Satellite data has confirmed global sea levels are rising faster each year.
Steve Nerem and collegaues from the University of Colorado Boulder analysed 25 years of satellite data and found that the rate of acceleration is about 0.08mm per year. At this rate, by the end of the century it could mean sea level rising by 1cm a year.
Sea levels go up as water either warms up and expands, or more water enters the oceans from melting ice sheets in Greenland and Antarctica. Both processes are happening due to climate change, but it is the increasing melting of the ice sheets causing the acceleration of sea-level rise.
“This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate–to more than 60 cm instead of about 30,” says Nerem.
“And this is almost certainly a conservative estimate.”
“Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that’s not likely.”
Using satellites to measure sea-level rise
The research team analysed satellite altimetry data. A satellite beams down a radar pulse, which is bounced back from the Earth’s surface and back to the satellite receiver.
By combining the altimetry data with the location of the satellite, researchers are able to measure sea-surface heights.
The research combined data from several satellite missions ranging back to 1992.
Detecting acceleration of sea-level rise is difficult even in a data set this large, because climate patterns like El Niño and La Niña can cause fluctuations in global sea level, as can large volcanic eruptions.
Mt Pinatubo erupted in 1991, just prior to the launch of the first satellite mission (Topex/Poseidon), which decreased global mean sea level. Climate models were used to account for the variation from these effects.
The data was cross-checked against tide gauge data.
“The tide gauge measurements are essential for determining the uncertainty in the GMSL (global mean sea level) acceleration estimate,” said co-author Gary Mitchum, USF College of Marine Science. “They provide the only assessments of the satellite instruments from the ground.”
25 years is just enough to provide an initial detection of acceleration, say the authors of this new study published in the Proceedings of the National Academy of Sciences.
The Jason-3 satellite, launched in 2016, will continue to provide sea-surface mapping data which will improve the reliability and robustness of the data.
Future research will focus on extending out the time series further, and refining the models to be able to better predict the impacts at a regional level.
Research published in PNAS.