Iceland volcano unlikely to cause global cooling
The eruption of Mt. Eyjafjallajokull in Iceland has had a chilling effect on air travel, but unless the eruption starts lofting far greater amounts of volcanic material higher into the atmosphere than it has to date, or continues unabated for months, the volcano with the tongue-twisting name probably will not join the ranks of famous climate-altering volcanoes, such as Mt. Tambora in Indonesia and Mt. Pinatubo in the Philippines.
Pinatubo, which blew its top in 1991, is famous for causing average global surface temperatures to drop by about one degree Fahrenheit in the one to two years following the eruption.
The Icelandic volcano, whose name, I suspect, can be traced to someone having an epileptic seizure while typing, has been spewing ash several miles high since last week, raising fears of another short-term, volcanically induced cool down. Although the ash plume has been sufficient to grind air travel to a screeching halt, most of the volcanic material has remained in the troposphere, where chemical processes and precipitation can disperse it in a matter of days, rather than entering the stratosphere where it would have a more enduring influence on the climate.
For example, an advisory from the UK Met Office yesterday told aviators that there was "no significant ash risk above flight level 350" (35,000 feet for those of you who don't speak pilot). Not only has the bulk of volcanic material stayed in the lower atmosphere, but the volcano has contributed a tiny fraction of the material that previous climate-disrupting volcanoes have released.
Volcanoes affect the climate by emitting both carbon dioxide, which causes warming, as well as particles known as aerosols, particularly sulfate aerosols, which cause cooling. Once they reach the upper atmosphere, these aerosols are very effective at reflecting incoming solar radiation, preventing it from reaching Earth's surface and thereby cooling the climate. This cooling can last as long as a few years, and is one of the many natural sources of climate variability.
The amount of carbon dioxide that volcanoes emit is extremely small compared to recent emissions from human activities. This graphic shows that daily emissions of carbon dioxide from European air travel dwarf the estimated emissions of the same gas from the volcano each day.
I asked Alan Robock, an environmental sciences professor at Rutgers University, to put this eruption into a historical context. He provided some startling statistics:
The April 14 eruption put out 0.003-0.004 megatons of sulfur dioxide into the troposphere, whereas the 1991 Pinatubo eruption added 20 megatons of sulfur dioxide to the stratosphere, he said.
"So this one was 10,000 times smaller, and put the sulfur dioxide into a region where its lifetime is only a week or so, as compared to one-two years in the stratosphere, so that's another factor of 100 smaller in terms of lifetime," Robock said via email.
Another factor that argues against this eruption having much influence on the global climate is its location. Iceland is almost perfectly situated to maximize the disruption of air traffic, while minimizing the impact on the climate system. The country sits upwind of Europe, and prevailing winds have carried the fine particles of ash, which are extremely hazardous to aircraft engines (see the case of British Airways flight 9 in 1982), above European hubs like London, Paris and Frankfurt. However, because of the way air circulates within the stratosphere, it can be especially difficult for a volcano located so far north to significantly alter the global climate.
According to the National Center for Atmospheric Research in Boulder, Colo., air primarily enters the stratosphere over the tropics, and the circulation carries it from there toward the poles, where it descends back to the troposphere. Because of this pattern, known as the Brewer-Dobson circulation, an eruption in the tropics can rapidly spread volcanic material worldwide, whereas emissions from a high-latitude volcano would have a more narrow influence on the climate in the northern hemisphere.
The volcano will not have a noticeable effect on North American weather in the near-term, although some ash has drifted to northeastern Canada, where flight restrictions are possible today, according to CNN. As the ash circulates around the Northern Hemisphere there may be more vibrant sunsets than normal, according to Weather Underground meteorologist Jeff Masters, who wrote last week:
It does not appear that the current eruption... was large enough to alter the atmospheric circulation of the Northern Hemisphere and cause a change in the late spring/early summer weather patterns. A series of several major eruptions over the next few weeks would be required for that to happen. The volcano is also too far north for the cooling effect of its ash cloud to affect the sea surface temperatures in the tropical Atlantic for the coming hurricane season. However, the ash could should bring spectacular sunsets to Europe over the next week, and to North America by sometime next week, as the jet stream wraps the ash cloud eastwards across the Northern Hemisphere.
History does argue in favor of caution, though, considering that Icelandic volcanoes, including Eyjafjallajokull's neighbor, Mt. Laki, have been blamed for triggering significant cooling spells in the past.
According to the blog realclimate.org, a long-duration eruption of Mt. Laki in 1783-84 had "significant climate effects."
"The crucial factor was that the eruption was almost continuous for over 8 months which lead to significantly elevated sulphate concentrations for that whole time over much of the Atlantic and European regions, even though stratospheric concentrations were likely not particularly exceptional," NASA scientist and blogger Gavin Schmidt wrote in 2006.
Only time will tell how long this eruption will last, and whether it may prevent this year from becoming the warmest year on record, as some NASA scientists have projected.
The views expressed here are the author's alone and do not represent any position of the Washington Post, its news staff or the Capital Weather Gang.
| April 19, 2010; 10:45 AM ET
Categories: Climate Change, Freedman, Nature, News & Notes, Science
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