I’m sure everyone is aware of the recent eruption of the Chaitén Volcano in southern Chile. There have been some pretty amazing photographs, satellite images, and videos. Besides the obvious negative effects to the local people, what other possible climate effects will this eruption have? We can use previous volcanic eruptions to learn what aspect of a volcanic eruption influences the global temperatures.

Solid, Liquid, or Gas?

Before the effects of a volcanic eruption can be determined, first we need to know what comes out of a volcano. The most obvious substance is the liquid hot magma (molten rock). In explosive volcanoes this is ejected into the atmosphere as tephra, which I think most of us would simply call “ash”.
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There has been much discussion lately about the recent “cooling trend” in the blogosphere. RealClimate has offered up a bet that there won’t be any long-term cooling. Roger Pielke Sr. offered his commentary. James Annan covered it not once, but twice. And William Connolley had a go at it as well.

This week offers a different cooling article in the Journal of Geophysical Research by Monaghan, et al. They looked at the Recent variability and trends of Antarctic near-surface temperature. Anthony Watts has posted on it, mostly quoting from a press release. Interestingly, the image he shows is from a NASA satellite study (which looks wrong) while the paper in question uses surface stations.
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New Scientist had an article recently titled How cleaning up America dried up the Amazon by Mason Inman. It reported on a Nature paper by Cox et al., Increasing risk of Amazonian drought due to decreasing aerosol pollution. This paper shows that positive changes can have unintended consequences long distances from their source.

The gist is that the sulfates generated in the United States reflect incoming solar radiation. But the amount of these aerosols has been decreasing since the 1970s, when anti-pollution laws started restricting the amount of aerosols in the atmosphere. Since there are now less sulfates in the atmosphere, more radiation is being absorbed by the ocean near the United States. This change in where the radiation is absorbed may have changed the storm tracks in the North Atlantic, bringing them farther North. This has led to less rainfall in the Amazon rainforest.
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Temperature is not the best metric to assess global warming. There are several reasons to use temperature when discussing global warming. The first is that most lay people can understand what a temperature is. Energy is a more difficult concept to grasp, even though they are essentially the same thing. To get the change in energy from a change in temperature, assuming nothing else changes, one need only multiply by a constant.

But as Dr. Pielke points out on his blog What Does Moist Enthalpy Tell Us?, there can actually be a decrease in surface temperature but an increase in surface energy if the water vapor content increases. He uses the example of Yuma, Arizona.
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