Seas around the world have risen an average of 7.6 centimetre since 1992, with some locations rising more than 23 centimetres due to natural variation, according to the latest satellite measurements from NASA and its partners.
The space agency is now providing its observations and analysis for an intensive research effort that points to an unavoidable rise of a metre or more in the future.
“We’ve seen from the paleoclimate record that sea level rise of as much as 10 feet in a century or two is possible, if the ice sheets fall apart rapidly,” said Tom Wagner, the cryosphere program scientist at NASA Headquarters in Washington.
“We’re seeing evidence that the ice sheets are waking up, but we need to understand them better before we can say we’re in a new era of rapid ice loss.”
NASA has been recording the height of the ocean surface from space since 1992. That year, NASA and the French space agency, CNES, launched the first of a series of spaceborne altimeters that have been making continuous measurements ever since. The first instrument, Topex/Poseidon, and its successors, Jason-1 and -2, have recorded about 2.9 inches (7.4 centimeters) of rise in sea level averaged over the globe.
In the 21st century, two new sensing systems have proven to be invaluable complements to the satellite altimetry record. In 2002, NASA and the German space agency launched the Gravity Recovery and Climate Experiment (GRACE) twin satellites. These measure the movement of mass, and hence gravity, around Earth every 30 days. Earth’s land masses move very little in a month, but its water masses move through melting, evaporation, precipitation and other processes. GRACE records these movements of water around the globe. The other new system is the multinational Argo array, a network of more than 3,000 floating ocean sensors spread across the entire open ocean.
But not everyone is affected equally, NASA says. According to the 23-year record of satellite data from NASA and its partners, the sea level is rising a few millimeters a year.
If you live on the US East Coast, though, your sea level is rising two or three times faster than average. If you live in Scandinavia, it’s falling. Residents of China’s Yellow River delta are swamped by sea level rise of more than nine inches (25 centimeters) a year.
“A lot of the major uncertainty in future sea level rise is in the Greenland Ice Sheet,” said OMG principal investigator Josh Willis, a scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.
At about 660,000 square miles (1.7 million square kilometers), the ice sheet is three times the size of Texas. It’s about a mile deep on average and contains enough water to raise global sea levels about 20 feet (6 meters), if it were all to melt.
“The question is how fast it’s melting,” Willis said.
You can see the results of the research in greater detail at the NASA website, Rising Seas: Frontiers of Climate Science
Bill Condie is a science journalist based in Adelaide, Australia.
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