Sulfur dioxide gas released from small volcanic eruptions could be slowing the progression of global warming, according to new research.
Climatologists and meteorologists have long known that the gas is capable of cooling the planet, but the contribution of smaller eruptions has, until now, been deemed insignificant. New research shows small volcanic eruptions alter temperatures by 0.09 and 0.22 degrees Fahrenheit since 2000, twice as much as previously estimated.
Sulfur dioxide combines with oxygen high in the atmosphere, forming molecules of sulphuric acid which can remain in the air for years before falling to the surface as acid rain. While locked in the atmosphere, this material can reflect sunlight back to space, cooling the surface.
The global warming hiatus, a reduction in rising temperatures seen over the last 15 years, could be explained by the eruptions of small volcanoes, researchers hypothesize. Previous theories suggested oceans may be acting as a heat sink, or reduced solar activity.
Climate models normally do not include the effects of minor eruption, due to the great difficulty of predicting such events. Large eruptions, like that of Mount Pinatubo in the Philippines in 1991 were included in such calculations. That event released 44 billion pounds of sulfur into the atmosphere.
The warmest year on record was 1998, after which global warming slowed, contrary to predictions made using computer simulations. This suggested that another factor - something unaccounted for in virtual models - was affecting the atmosphere of the Earth. Researchers examining the question noticed ordinary water vapor may be blocking ground observations of the atmosphere between six and nine miles above the surface. This is where the troposphere, the lowest layer of the atmosphere, turns into the stratosphere.
Satellites are often used to measure concentrations of sulfur dioxide and other aerosols, but those observations may be affected by water. The new research combines data collected from space with ground-based observations, in order to overcome any affect from water vapor in the upper troposphere.
"The satellite data does a great job of monitoring the particles above [10 miles], which is fine in the tropics. However, towards the poles we are missing more and more of the particles residing in the lower stratosphere that can reach down to [6.25 miles]," David Ridley from the Massachusetts Institute of Technology (MIT), said.
A Lidar laser system was used to illuminate the atmospheric contaminant, and reflected light was compared to satellite and balloon measurements, as well as readings from the ground-based Aeronet network.
"This is part of the story about what has been driving climate change for the past 15 years. It's the best analysis we've had of the effects of a lot of small volcanic eruptions on climate," Ridley said.
Examination of the role of small volcanic eruptions in cooling global temperatures was detailed in the journal Geophysical Research Letters.
