Small volcanic eruptions might help to slow global warming

The Sarychev Peak Volcano on Matua Island in the northwest Pacific erupting in June, 2009. According to new research, small eruptions such as this may have contributed to a slowdown in global warming.

Scientists have long known that volcanic eruptions can cool the atmosphere. For instance it has been estimated the eruption of Mount Pinatubo in the Philippines in 1991 corresponded to a global temperature drop of 0.5 degrees Celsius.

But the Pinatubo eruption was massive, ejecting an estimated 20 million metric tonnes of sulfur into the atmosphere. (Sulfur in the upper atmosphere reflects sunlight away from the Earth and lowers temperatures.) Previous research has suggested that smaller eruptions do not contribute significantly to this phenomenon.

But new ground, air and satellite measurements show that small volcanic eruptions that took place between 2000 and 2013 have deflected almost twice as much solar radiation as previously estimated. According to a new study in Geophysical Research Letters, the data could explain why increases in global temperatures have slowed over the past 15 years, a period called the "global warming hiatus".

The warmest year on record is 1998. After that, the steep climb in global temperatures appeared to level off. Scientists have previously suggested weak solar activity or heat uptake by the oceans could be responsible.

Climate projections don't typically take volcanic eruptions into account, because of their unpredictability. The new study combined observations from ground, air and space-based instruments to better observe the fine suspended particles, or aerosols, that erupting volcanoes spew into the atmosphere. The researchers from MIT found the aerosols from volcanoes may have been sufficient to lower global surface temperatures by 0.05 to 0.12 degrees Celsius.

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