This week's physics central podcast is about hot and cold. Volcanoes—which spew material that reaches thousands of degrees Fahrenheit—can actually cool the planet. Volcanoes eject aerosols that reflect sunlight, and climate scientists have observed the cooling effects of major volcanic events in 1991 and 1982. Those effects can sometimes take years to reverse. New research in the journal Nature Geophysics has shown that the combination of minor volcanic events between 1998 and 2010 had a measurable cooling effect on the Earth.
This is a big deal because it partly explains the so-called global warming slow-down: a decrease in the acceleration of rising global temperatures. For the most part, climate models have not been able to replicate the slow-down. But most of those models do not include recent volcanic activity as a cooling factor.
In 2011, Susan Solomon and colleagues at MIT wrote a paper showing that the volcanic contribution from 1998 to 2010 was likely large enough to have a significant cooling effect on the earth. The new work by Ben Santer and colleagues at Lawrence Livermore National Laboratory provides the quantitative evidence to back up Solomon's conjecture.
Using satellite data going back to 1998, Santer and his team measured the extent to which volcanic aerosols blocked sunlight and moonlight coming through the atmosphere. They estimate that volcanic activity may be responsible for 15 to 20% of the global warming slow-down.
The results counter the notion that climate models do not predict the slow-down because they are "oversensitive" to greenhouse gasses. Santer emphasized that this logic is flawed for multiple reasons, but the new results offer more clear evidence against it.
This new information will help scientists make better predictions about future climate conditions (it is already being incorporated into climate models), but it don't be mislead by the title of this post: these cooling effects do not reverse the effects of climate change. If volcanic activity and other cooling effects are reduced in the future, temperatures will once again start to soar.