Sea levels over the past two decades have risen faster than previously thought, suggests a new study that reassesses the accuracy of satellite data.

The study by an international team of scientists, published Monday in Nature Climate Change , compares satellite records of sea levels made from 1993 to mid-2014 to tide gauge records.

Lead author and geophysicist Christopher Watson says the study results address an ongoing puzzle about sea level rise.

Previous studies based on tide gauge or satellite data alone have suggested a slowing in the rate of sea level rise over the past decade relative 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," says Watson, senior lecturer at the University of Tasmania.

SEALEVEL-FLOODING/CHESAPEAKE

Remains of trees in a coastal ghost forest display rising sea levels on Assateague Island in Virginia. Since 1992, sea levels in some parts of the world have risen more than 25 cm (9 inches) and other regions, such as along the U.S. West Coast, actually falling, according to an analysis of 23 years of satellite data. (Kevin Lamarque/Reuters)

But comparison of the satellite and hourly tide gauge data, factoring in the land movements around those gauges, suggests that sea levels have risen faster since 1993 relative to slower rate in previous decades.

Errors in satellite record corrected

The study also corrects long-standing errors in the satellite record of sea levels, finding that the global mean rate of sea level rise between 1993 and mid-2014 is between 2.6 and 2.9 millimetres per year.

Previous studies overestimated the average annual rate of sea level rise over the period. Most of this overestimation of sea level rise occurred earlier in the record, from 1993 to1999, which distorted the bigger picture, and concealed the trend of accelerating sea level rise.

The measurement errors, known as 'bias drift', could be due to degradation of the electronics in the first satellite in the series, called Topex Poseidon, Watson says, although work is continuing to establish the cause.

The degree of difference between the original and revised measurements is only around 10 to 15 per cent — amounting to differences of 0.9 to 1.5 millimetres per year — but it paints a revised picture of a recent acceleration in sea level rise, which is much closer to predictions.

With only just over two decades of satellite monitoring, the fluctuations in sea level could just be the result of annual variability, but the data suggests a trend is emerging, says Watson.

"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]," says Watson.

The IPCC forecast global sea levels to rise up to 98 centimetres by 2100 — if greenhouse gases continue unabated — or between 28 and 61 centimetres if emissions are mitigated.

An acceleration in the rate of global sea level rise could have significant impacts on coastal regions, says Watson.