Global sea level rise has been assumed to have been rising at an average rate of 1.5 centimeters (0.6 inches) per decade since 1900, as measured by NOAA. However, a new study has cast that figure into doubt: after having taken regional sea level increases into account, the previously accepted rate may be off by a great deal — from 5 to 28 percent in some regions.

The problem comes from the fact that sea level measurements have been historically taken from coastal tide gauges, from roughly a dozen select sites around the northern hemisphere. It was assumed in the past that ocean levels were rising relatively evenly across the globe, however:

“It’s not that there’s something wrong with the instruments or the data, but for a variety of reasons, sea level does not change at the same pace everywhere at the same time,” explains study lead Philip Thompson, associate director of the University of Hawai’i Sea Level Center.

Specifically, sea levels have been increasing faster in the southern hemisphere — precisely where the majority of these tidal gauges are not. The study has found that the last century saw much higher average sea level rises across the globe, somewhere between 14 centimeters (5.5 inches) and 17 centimeters (6.7 inches).

The rapid rise of sea levels in the southern hemisphere has presented a conundrum to scientists, since ice melt has been more rapid in the Arctic, as opposed to the Antarctic. As it turns out, the influences made by factors such as wind patterns and volume increases due to increased temperature, can create “ice melt fingerprints" for individual regions, marking how sea level rise is affected.

“This is really important, because it is possible that certain melt fingerprints or the influence of wind on ocean circulation might cause us to overestimate past sea level rise,” continues Thompson. “But these results suggest that is not likely and allow us to establish the minimum amount of global sea level rose that could have occurred during the last century.”