Volcanic eruption masked acceleration in sea level rise

NSF | AUGUST 12, 2016

The cataclysmic 1991 eruption of Mount Pinatubo in the Philippines masked the full impact of greenhouse gases on accelerating sea level rise, according to a new study.

Mount Pinatubo's 1991 eruption and its effects masked sea level rise. Image credit: USGS

Satellite observations of the ocean surface, which began in 1993, indicated the rate of sea level rise was holding fairly steady at about 3 millimeters per year. As the pace of warming oceans and melting glaciers and ice sheets accelerated, scientists expected to see a corresponding increase in the rate of sea level rise. Analysis of the satellite record has not borne that out, however.

Researchers have now determined that the expected increase in sea level rise due to climate change was likely hidden because of a happenstance of timing: Pinatubo erupted in 1991, two years before the first satellite observations of the ocean began. The eruption, which temporarily cooled the planet, caused sea levels to drop and effectively distorted calculations of sea level rise in subsequent decades.

Analyzing the simulations, the research team found that Pinatubo's eruption caused the oceans to cool and sea levels to drop by about 6 millimeters.

As the sunlight-blocking aerosols from Mount Pinatubo dissipated in the simulations, sea levels began to slowly rebound to pre-eruption levels. This rebound swamped the acceleration caused by the warming climate and made the rate of sea level rise higher in the mid- and late 1990s than it otherwise would have been.

The study lends support to climate model projections that show the rate of sea level rise escalating over time as the climate warms.

Understanding whether the rate of sea level rise is accelerating or remaining constant is important because it drastically changes what sea levels might look like in 20, 50 or 100 years.

Because the study's findings suggest that acceleration due to climate change is already under way, the acceleration should become evident in the satellite record in the coming decade.

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