Volcanoes helped slow ocean warming trend, researchers find

Feb 09, 2006
The June 12, 1991 eruption column from Mount Pinatubo, Philippines, as seen from Clark Air Base
The June 12, 1991 eruption column from Mount Pinatubo, Philippines, as seen from Clark Air Base. Credit: Richard P. Hoblitt/USGS

Ocean temperatures might have risen even higher during the last century if it weren't for volcanoes that spewed ashes and aerosols into the upper atmosphere, researchers have found. The eruptions also offset a large percentage of sea level rise caused by human activity.

Using 12 new state-of-the-art climate models, the researchers found that ocean warming and sea level rise in the 20th century were substantially reduced by the 1883 eruption of the Krakatoa volcano in Indonesia. Volcanic aerosols blocked sunlight and caused the ocean surface to cool.

“That cooling penetrated into deeper layers of the ocean, where it remained for decades after the event,” said Peter Gleckler, an atmospheric scientist at Lawrence Livermore National Laboratory (LLNL). “We found that volcanic effects on sea level can persist for many decades.”

Gleckler, along with LLNL colleagues Ben Santer, Karl Taylor and Krishna AchutaRao and collaborators from the National Center for Atmospheric Research, the University of Reading and the Hadley Centre, 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.

External “forcings,” such as changes in greenhouse gases, solar irradiance, sulphate and volcanic aerosols, were included in the models.

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.

The volume 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.

“The ocean warming suddenly drops,” he said. “Volcanoes have a big impact. The ocean warming and sea level would have risen much more if it weren't for volcanoes.”

Volcanic aerosols scatter sunlight and cause the ocean surface temperature to cool, an anomaly that is gradually subducted into deeper layers, where it remains for decades.

The experiments studied by Gleckler’s team also included the more recent 1991 Mt. Pinatubo eruption in the Philippines, which was comparable to Krakatoa in terms of its size and intensity. While similar ocean surface cooling resulted from both eruptions, the heat-content recovery occurred much more quickly in the case of Pinatubo.

“The heat content effects of Pinatubo and other eruptions in the late 20th century are offset by the observed warming of the upper ocean, which is primarily due to human influences,” Gleckler said.

The research appears in the Feb. 9 issue of the journal Nature.

Source: Lawrence Livermore National Laboratory

Explore further: SpaceX breaks ground on Texas rocket launch site

add to favorites email to friend print save as pdf

Related Stories

Kiribati leader visits Arctic on climate mission

Sep 20, 2014

Fearing that his Pacific island nation could be swallowed by a rising ocean, the president of Kiribati says a visit to the melting Arctic has helped him appreciate the scale of the threat.

Cape Cod saltmarsh recovery looks good, falls short

Sep 17, 2014

After decades of decline, grasses have returned to some once-denuded patches of Cape Cod's saltmarshes. To the eye, the marsh in those places seems healthy again, but a new study makes clear that a key service ...

Study finds Great Barrier Reef is an effective wave absorber

Sep 17, 2014

New research has found that the Great Barrier Reef is a remarkably effective wave absorber, despite large gaps between the reefs. This means that landward of the reefs, waves are mostly related to local winds rather than ...

Recommended for you

Gravitational waves according to Planck

3 hours ago

Scientists of the Planck collaboration, and in particular the Trieste team, have conducted a series of in-depth checks on the discovery recently publicized by the Antarctic Observatory, which announced last spring that it ...

Infant solar system shows signs of windy weather

3 hours ago

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have observed what may be the first-ever signs of windy weather around a T Tauri star, an infant analog of our own Sun. This may help ...

Finding hints of gravitational waves in the stars

10 hours ago

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

User comments : 0