Satellite Data Underestimated how Fast Sea Levels Were Rising

The oceans are rising faster than scientists thought.

[e]Luis Galdamez/Xinhua Press/Corbis

When scientists measure sea level rise from space their calculations must meticulously account for the distance between the surface of the water and the bottom of the ocean. And according to a new study published by the journal Nature Climate Change, small errors in those measurements made by mapping satellites resulted in data that indicted the oceans were rising slower than they actually are.

Previously, data taken from satellites dating back to 1993 showed that rate of sea level rise slowed down over the last decade when compared to the one before it. "That was a puzzle because it coincides with a period where we've got increasing water from West Antarctica and Greenland," lead author and geophysicist Christopher Watson told the Australian Broadcasting Corporation.

But what this new analysis found was that between 1993 to 1999 one satellite overestimated the amount of sea level rise it saw. When that satellite, the Topex Poseidon, was eventually replaced, the new equipment took more accurate measurements that corrected for the original mistakes. However, this made it appear as if the rate of sea level rise slowed down instead of speeding up. And that didn't make a whole lot of sense to scientists.

“A deceleration over the last 30 years would be a bit hard to understand, although natural variability can mess with trends over shorter time periods like this,” writes Scott K. Johnson for Ars Technica. “Acceleration like this is what we expect to see, particularly as the contribution of Greenland and western Antarctica, which are both losing ice, has also accelerated over this time period.”

The degree of difference between the mistaken and corrected data amounts to a difference of 0.9 to 1.5 millimeters per year. It might not look like much on paper, but when applied across oceans worldwide, even small difference becomes more dire. "What our revised record really does indicate is an acceleration and that is consistent with the projections of sea level from IPCC [Intergovernmental Panel on Climate Change]," Watson tells the ABC. According to the IPCC forecasts, sea levels could rise almost three feet by 2100 if emissions of greenhouse gas aren’t mitigated.

Get the latest stories in your inbox every weekday.