May 12 2008
Possible Effects of Chaitén Volcano
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”.
Upon reaching the surface, the magma is quickly condensed into a solid. Wikipedia has a nice article on the effects of volcanic ash. The cloud plume seen in photos is partially caused by the small ash particles. The Wikipedia article states that the visible plume is also composed of steam (water vapor), which is wrong. Water vapor in the atmosphere is colorless. The water will condense to form liquid droplets, also known as clouds.
Typical Volcanic Gaseous Emissions
But volcanoes also emit a lot of gases into the atmosphere; the most abundent being water vapor. The also emit carbon dioxide, sulpher dioxide, diatomic hydrogen, carbon monoxide, hydrogen sulfide, hydrogen chloride, and hydrogen flouride. The amounts of these typical gases released at a sampling of volcanoes can be seen at the link above.
Several of these are greenhouse gases. However, the amount of CO2 released from volcanoes each year is far less than by human. For instance, Gerlach (1991, EOS) estimated that human emissions of CO2 were 2 orders of magnitude larger than natural sources.
The real effects come from the sulphur dioxide gas that is injected into the stratosphere. This gas chemically reacts with oxygen to form sulphate aerosols (solid particles) which have different optical properties than the sulpher dioxide gas. Most importantly, it is now ‘white’, meaning that it reflects light at visible wavelengths.
Wet and Dry Deposition
There are two main processes to remove particles from the atmosphere: dry and wet deposition. Dry deposition is the most intuitive: they fall out due to gravitational settling. For large objects where the drag force is small compared to the force of gravity (such as a basketball), the time for the aerosol to settle is small. For small objects (such as sulphate aerosols), the time to settle is large.
Luckily, these aerosols can be used as cloud condensation nuclei (CCN). For cloud drops to form, they need a nucleus to initially condense upon. If that cloud drop becomes large enough, it falls to the ground as rain with the aerosol still inside of it.
Stratospheric Aerosols
As it turns out, the primary mode of aerosol removal in the troposphere is through wet deposition. That means that most aerosols will have an average time in the atmosphere about the same as the water droplets that remove them. This turns out to be a small 7-10 days.
However, there is no wet deposition in the stratosphere. So the only way for these particles to be removed is through dry deposition, gravity. The residence time for aerosols in the stratosphere is around 2 years. This is the major impact of volcanoes on the temperature of the planet. These aerosols reflect incoming solar radiation and cool the surface.
What about Chaitén?
Will the recent Chaitén eruption cause a global surface cooling? Probably. But the eruption of Pinatubo is 1991 was fairly large, and it only had a modest effect on temperature for a short time.
References:
Gerlach, T.M., 1991, Present-day CO2 emissions from volcanoes: Eos, Transactions, American Geophysical Union, Vol. 72, No. 23, June 4, 1991, pp. 249-255.
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6 Responses to “Possible Effects of Chaitén Volcano”
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From Wikipedia:
This very large stratospheric injection resulted in a reduction in the normal amount of sunlight reaching the earth’s surface by roughly 10% (see figure). This led to a decrease in northern hemisphere average temperatures of 0.5–0.6 °C (0.9–1.1 °F), and a global fall of about 0.4 °C (0.7 °F).
Ok … if sunshine drops by 10% temperature drops by .6C.
What does a rise in Sunshine do?
Take a look at Sunshine in the UK for 2007.
http://www.metoffice.gov.uk/climate/uk/2007/sunshine.html
http://www.sciencemag.org/cgi/content/abstract/308/5723/847?ck=nck
“Newly available surface observations from 1990 to the present, primarily from the Northern Hemisphere, show that the dimming did not persist into the 1990s. Instead, a widespread brightening has been observed since the late 1980s. This reversal is reconcilable with changes in cloudiness and atmospheric transmission and may substantially affect surface climate, the hydrological cycle, glaciers, and ecosystems. ”
If there is warming, how can you claim it is CO2 when more sunshine is reaching the NH?
“Gerlach (1991, EOS) estimated that human emissions of CO2 were 2 orders of magnitude larger than natural sources.”
I haven’t looked at that in particular, but I remember seeing much different figures. According to the UNEP natural sources is 20 about times that of humans, and I’ve seen other figures. In the back of my head I remember that human caused emissions was about 4 _someunits_ of CO2 out of a total of 118 _someunits_, which makes it about 30ish. Sorry, I’m a bit lazy to dig up the units and the references, it’s late.
This article relates to this topic. It’ll be a while before it’s known if there will be any global effects.
http://volcanoes.suite101.com/article.cfm/climate_change_from_chaiten
Atmoz,
Thanks for the informative post. What can you find regarding industrial emissions of sulfates reaching the stratosphere? Have you seen pictures of some of the old Soviet industrial cities? Their everyday emissions looked like mini-volcanoes.
Volk (1996) showed that mid-latitude air is entrained into the stratosphere within about 13.5 months. Similar time scales would be expected for industrial sulfate emissions. As mentioned above, the residence time for tropospheric aerosols is around 7-10 days, so very little transport of tropospheric aerosols to the stratosphere is expected.
Turco et al. (1979) demonstrate with an eddy-diffusion model that there is an effective barrier for sulfates between the upper troposphere and lower stratosphere.
References:
Turco, R., P. Hamill, O. Toon, R. Whitten, and C. Kiang, 1979: A One-Dimensional Model Describing Aerosol Formation and Evolution in the Stratosphere: I. Physical Processes and Mathematical Analogs. J. Atmos. Sci., 36, 699–717.
Volk, C. M., J. W. Elkins, D. W. Fahey, R. J. Salawitch, G. S. Dutton, J. M. Gilligan, M. H. Proffitt, M. Loewenstein, J. R. Podolske, K. Minschwaner, J. J. Margitan, and K. R. Chan, 1996: Quantifying Transport Between the Tropical and Mid-Latitude Lower Stratosphere. Science, 272, (5269), 1763. DOI: 10.1126/science.272.5269.1763
Atmoz,
How can industrial CFC’s reach the stratosphere and not sulfates? By the way, eddy diffusion is chaotic, which means on occasion you are going to get a good whiff of sulfates in the stratosphere.