Volcanos Helped Slow Ocean Warming

Debris form a volcanic eruption that occurred more than a century ago still lingers in the Earth's upper atmosphere where it is helping to keep ocean temperatures cool and offset sea-level rising, a new study finds.

Spewed ashes and aerosols from the 1883 Krakatoa volcanic eruption in Indonesia are helping to block sunlight and reduce ocean temperature warming.

 "That cooling penetrated into deeper layers of the ocean, where it remained for decades after the event," said lead researcher Peter Gleckler from Lawrence Livermore National Laboratory.

The researchers tested the effects of volcanic eruptions on recent climate models. They examined model simulations of the climate from 1880 to 2000, comparing them with available observations.

They found that the average temperature of oceans (down to 300 meters) worldwide has warmed by roughly .037 degrees Celsius in recent decades due to increasing atmospheric greenhouse gases. While seemingly small, this corresponds to a sea level rise of several centimeters and does not include the effect of other factors such as melting glaciers. That sea level jump, however, would have been even greater if it weren't for volcanic eruptions over the last century, Gleckler said.

Oceans expand and contract depending on the ocean temperature. This causes sea level to increase when the water is warmer and to recede in cooler temperatures.

Gleckler's team also included the more recent 1991 Mt. Pinatubo [above image] eruption in the Philippines, which was comparable to Krakatoa in terms of its size and intensity.

The study was detailed in the Feb. 9 issue of the journal Nature.

--Ker Than

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Credit:  Richard P. Hoblitt/USGS