Most of the 20th Century Sea Level Rise Was Overestimated. Why That Makes the Recent Rise Worse?
melting ice berg

A new Harvard study looked at the level of sea rise recently and over the past century. In it, scientists are hoping to clear up one puzzle many scientists have tried to wrap their heads around.

Earlier estimates pegg water level rise between 1901-1990 at 1.5-1.8 millimeters per year. Study co-author Carling Hay and Eric Morrow say that figure should be around 1.2 millimeters per year. Scientists have been overestimating the rise in water in most of the 20th century by as much as 30%.

Hay and Morrow’s study does confirm the rapid rise in sea level rise since 1990 – 3 millimeters per year. “Unfortunately, our new lower rate of sea-level rise prior to 1990 means that the sea-level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought,” says Hays.

Estimating sea-level is quite challenging. According to Hays, scientists usually gather records from tide gauges located across the world. Seems simple, right? Well, accurate readings can be hard to come by. Measurements right along the coast don’t paint the whole picture. Wind, shifting land and other factors can influence these measurements.

To get these new estimates, the team looked at what they call sea-level ‘fingerprints.’ They used statistical models to parse data and determine a more accurate figure.

“What we were interested in — and remain interested in — was whether we can detect the sea-level fingerprints we predicted in our computer simulations in sea-level records,” Morrow said. “Using a global set of observations, our goal has been to infer how individual ice sheets are contributing to global sea-level rise.”

To do so, they have to account for a wide variety of factors – ice age signals, ocean circulation patterns, warming temperatures, etc.

While the overestimation of sea-level rise between 1901-1990 seems like good news on the surface, it shows the rise in the past twenty years is larger than previously thought.

The study/paper was published yesterday in the journal Nature.

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