From: American Geophysical Union
Published November 21, 2014 02:34 PM

Can Volcanic Eruptions Slow Global Warming?

Small volcanic eruptions might eject more of an atmosphere-cooling gas into Earth’s upper atmosphere than previously thought, potentially contributing to the recent slowdown in global warming, according to a new study.

Scientists have long known that volcanoes can cool the atmosphere, mainly by means of sulfur dioxide gas that eruptions expel. Droplets of sulfuric acid that form when the gas combines with oxygen in the upper atmosphere can remain for many months, reflecting sunlight away from Earth and lowering temperatures. However, previous research had suggested that relatively minor eruptions—those in the lower half of a scale used to rate volcano “explosivity”—do not contribute much to this cooling phenomenon.

Now, new ground-, air- and satellite measurements show that small volcanic eruptions that occurred between 2000 and 2013 have deflected almost double the amount of solar radiation previously estimated. By knocking incoming solar energy back out into space, sulfuric acid particles from these recent eruptions could be responsible for decreasing global temperatures by 0.05 to 0.12 degrees Celsius (0.09 to 0.22 degrees Fahrenheit) since 2000, according to the new study accepted to Geophysical Research Letters, a journal of the American Geophysical Union.

These new data could help to explain why increases in global temperatures have slowed over the past 15 years, a period dubbed the ‘global warming hiatus,’ according to the study’s authors.

The warmest year on record is 1998. After that, the steep climb in global temperatures observed over the 20th century appeared to level off. Scientists previously suggested that weak solar activity or heat uptake by the oceans could be responsible for this lull in temperature increases, but only recently have they thought minor volcanic eruptions might be a factor.

Climate projections typically don’t include the effect of volcanic eruptions, as these events are nearly impossible to predict, according to Alan Robock, a climatologist at Rutgers University in New Brunswick, N.J., who was not involved in the study. Only large eruptions on the scale of the cataclysmic 1991 Mount Pinatubo eruption in the Philippines, which ejected an estimated 20 million metric tons (44 billion pounds) of sulfur, were thought to impact global climate. But according to David Ridley, an atmospheric scientist at the Massachusetts Institute of Technology in Cambridge and lead author of the new study, classic climate models weren’t adding up.

Continue reading at the American Geophysical Union.

Volcano image via Shutterstock.

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