Scientists Report Unusual Rise in Ocean Level

Scientists are keeping an eye on an unusual rise in sea level that, if it persists, could have a dramatic impact on the world’s coastlines.

Satellite data show sea level has risen more than a tenth of an inch in each of the past two years. Researchers said the rise was about twice that detected by land-based gauges over the past century. If the trend continues, they said, it could signal an accelerated increase in ocean depth, evidence that Earth is warming up.

A report on the study was published Friday in the journal Science.

R. Steven Nerem, a National Aeronautics and Space Administration scientist, said measurements in 1993 and 1994 detected an average annual sea-level rise of 3.9 millimeters.

Nerem said this is about double the increase detected worldwide in a century of tidal gauge readings, but he cautioned that the rate of increase may be temporary.

“We’re pretty sure that part of the rise we see is due to El Nino (a periodic weather pattern) and part of it is due to climate change,” Nerem said.

El Nino is a Pacific Ocean phenomenon in which a warm water current changes its usual pattern. This, in turn, has a global weather impact.

Nerem said El Nino’s warming of cold water could have caused a thermal expansion of water molecules that, over the vast expanse of the ocean, is enough to show up as a slight rise in sea level.