photo: Jim Maes/Creative Commons
With the recent eruption of Mount Merapi in Indonesia this one is particularly apropos: Scientists from Columbia University have discovered that over the past 800 years, major volcanic eruptions have caused to significant shifts to rainfall patterns across Asia, and in ways that were opposite of what has been predicted in many climate change models.
Mount Pinatubo erupting in 1991. Photo: Wikipedia.
Looking at tree-ring data, researchers from the Lamont-Doherty Earth Observatory found that while much of Central Asia became drier in the aftermath of major volcanic activity, Southeast Asia became wetter.
The part at deviance from many climate models is this: It was generally thought that the increase in sulfate particles in the atmosphere caused by the eruptions would deflect solar radiation and cool the Earth, also causing less surface evaporation and lowering rainfall.
Obviously that did occur in Central Asia, where drier conditions persisted for a couple years after the eruptions, but it's unknown why the exact opposite occurred in elsewhere.
Summit caldera of Mount Tambora, Indonesia. Photo: Wikipedia.
Atmospheric Cycles Could Counteract or Reinforce Volcano Effect
One possible reason put forth is that atmospheric cycles such as El Niño could counteract the volcanic effect.
Kevin Anchukaitis, lead author of the study, noted however that if volcanic eruptions and these atmospheric cycles came together at the right time, they could reinforce one another. "Then you get flooding or drought, and neither flooding nor drought is good for the people living in the regions."
As for the Mount Merapi eruption, the LDEO scientist say that it isn't large enough to be able to trigger large-scale changes in weather--for that you need something the size of the 1991 eruption of Mount Pinatubo in the Philippines or the 1815 eruption of Mount Tambora in Indonesia.
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More on Volcanoes:
Global Warming Versus the Volcano: Could Eruptions Slow Climate Change?
Ask Pablo: What Impact Will The Volcano In Iceland Have On Climate Change?
Geoengineering Inspired by Volcanoes? Not It You Want to Avoid Destroying Our Lakes