Volcanic Eruptions Partly Behind Global Warming 'Pause'

Volcanic eruptions are partly behind the global warming "pause" that has occurred over the last 15 years, according to a new study, effectively cooling the atmosphere 0.05 degrees to 0.12 degrees Celsius (32.09 - 32.216 F) since 2000.

From 1998-2013, the planet has experienced a "warming hiatus" or "pause" during which the average surface temperature on Earth has barely risen, causing people to question the reality of global warming. Scientists insist that this lull won't last forever, and cite natural cooling fluctuations, solar irradiance and heat uptake by the oceans as reasons for the contradiction. And now, researchers are partially blaming small volcanic eruptions for the pause as well.

"This new work shows that the climate signals of late 20th- and early 21st-century volcanic activity can be detected in a variety of different observational data sets," lead study author Benjamin Santer, from the Lawrence Livermore National Laboratory, said in a statement.

When volcanoes spew out sulfur dioxide during an eruption - formed when the gas combines with oxygen in the upper atmosphere - it reflects sunlight away from the Earth. This lowers temperatures at both the surface and the upper atmosphere, and can persist for many months.

Previous research suggested that only extremely large eruptions would be able to cause such a drastic impact on the global climate - for example, the 1991 Mount Pinatubo eruption in the Philippines, which released an estimated 20 million metric tons (44 billion pounds) of sulfur into the atmosphere. But now, according to more accurate aerosol measurements using ground-, air- and space-based instruments, it seems that smaller eruptions are just as effective.

That's because prior satellite measurements missed data from the stratosphere and the troposphere - the lowest layer of the atmosphere, where all weather takes place. Those layers meet between 10 and 15 kilometers (six to nine miles) above Earth.

"The fact that these volcanic signatures are apparent in multiple independently measured climate variables really supports the idea that they are influencing climate in spite of their moderate size," said co-author Mark Zelinka. "If we wish to accurately simulate recent climate change in models, we cannot neglect the ability of these smaller eruptions to reflect sunlight away from Earth."

The findings were published in the journal Geophysical Research Letters.

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