The latest NASA satellite data reveals global oceans have risen by an average of three inches, and by as much as nine inches in some locations, since 1992. An ominous new analysis based on these finding suggest an "unavoidable rise" in sea levels in the future.
Members of NASA's new interdisciplinary Sea Level Change Team are now working to predict how quickly these potentially devastating changes will occur.
"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," said Steve Nerem of the University of Colorado, Boulder, and lead of the Sea Level Change Team. "But we don't know whether it will happen within a century or somewhat longer."
In 2013, the United Nations Intergovernmental Panel on Climate Change (IPCC) made an assessment based on a consensus of international researchers suggesting the global sea levels will rise by between one and three feet by the end of the century; these new findings suggest the higher end of the suggested range is most probable. The new data shows the height of the sea surface is not rising uniformly in every region, and these variations are largely driven by the effects of ocean currents and natural cycles like the Pacific Decadal Oscillation (PDO).
"Sea level along the west coast of the United States has actually fallen over the past 20 years because long-term natural cycles there are hiding the impact of global warming," said Josh Willis, an oceanographer at NASA's Jet Propulsion Laboratory (JPL). "However, there are signs this pattern is changing. We can expect accelerated rates of sea level rise along this coast over the next decade as the region recovers from its temporary sea level 'deficit.'"
The researchers estimated about one-third of sea level rise is linked to the expansion of warm ocean water, one-third is due to ice loss from the Greenland and Antarctic ice sheets, and the final third is from melting mountain glaciers. The researchers are not sure if this ratio will remain stable in future decades, or if the polar ice sheets will begin to melt more quickly and become a larger contributor to sea level rise.
"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, of 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."
The Greenland ice sheet's contribution to sea level rise is currently much greater than Antarctica's, but the researchers believe their roles could one day reverse. In 2014, two West Antarctica studies suggested glaciers in this region are headed for a major collapse. A recent study also found two deep troughs beneath a major East Antarctic glacier that could draw in warm water and cause it to melt more rapidly.
"The prevailing view among specialists has been that East Antarctica is stable, but we don't really know," said glaciologist Eric Rignot of the University of California Irvine and JPL. "Some of the signs we see in the satellite data right now are red flags that these glaciers might not be as stable as we once thought. There's always a lot of attention on the changes we see now, but as scientists our priority needs to be on what the changes could be tomorrow."
To gain more isnight into future glacial melt, The Oceans Melting Greenland (OMG) project is taking coastal ocean temperature measurements and observing thinning around local ice sheets. The team plans to create the first high-resolution maps of the seafloor.
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