Scientists warned that the rate of global sea level rise has been overestimated, Science Daily reported.

This means ocean levels are rising at a much faster rate over the past two decades compared to the previous predictions by scientific organizations.

Harvard University scientists Carling Hay and Eric Morrow came up with this surprising finding after reviewing past sea level rise estimates from 1900 to 1990.

Back then, ocean levels were predicted to rise by 1.5 to 1.8 millimeters every year. However, during those decades, Hay and Morrow said ocean levels actually rose by an average of 1.3 millimeters annually.

The problem, however, as pointed out by Morrow, is that current projections are based on the 1900 to 1990 estimates. Based on these data, it was agreed that the sea level has increased by 3 millimeters annually over the past two decades.

Since the sea level rise has been overestimated, the 3-millimeter increase can no longer be considered an accurate prediction.

"Another concern with this is that many efforts to project sea-level change into the future use estimates of sea level over the time period from 1900 to 1990," Morrow said in a statement.

"If we've 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," he continued.

For the years following 1990, the scientists turned to computer models and satellite data to gather a more accurate prediction. These methods are certainly more complex compared to the previous practice of using yard sticks to gather average measurements of rising ocean tides.

"Our estimates from 1993 to 2010 agree with [the prior] estimates from modern tide gauges and satellite altimetry, within the bounds of uncertainty," Hay told the BBC. "But that means that the acceleration into the last two decades is far worse than previously thought."

"This new acceleration is about 25% higher than previous estimates," she added.

Morrow and Hay attributed the rise in sea levels to the changing ocean patterns and present-day effects of global warming.