Sea level rise continues to accelerate.

• Position: Global Warming

The acceleration of global sea level change from the end of the 20th century through the last two decades significantly has been swifter than scientists thought, according to a study in Nature.

Coauthored by earth scientists Carling Hay and Eric Morrow, the study shows that calculations of global sea-level rise from 1900-90 had been overestimated by as much as 30%. Previous estimates had placed sea-level rise at between 1.5 and 1.8 millimeters annually in the 20th century. Hay and Morrow suggest that, from 1901-90, the figure was closer to 1.2 millimeters per year. However, global sea level has risen by about three millimeters annually since that time.

"Many efforts to project sea-level change into the future use estimates of sea level over the time period from 1900-90," Morrow notes. "If we have been overestimating the sea-level change during that period, it means that these models are not calibrated appropriately, and that calls into question the accuracy of projections out to the end of the 21st century."

Hay and Morrow approached the challenge of estimating sea-level rise from a new perspective. Typically, according to Hay, estimates of sea-level rise are created by dividing the world's oceans...