Um vulcão, cujo nome é um palavrão, mexe com o mundo

Depois de "dormir" por quase 2 séculos (sua erupção anterior deu-se em 1821, e durou dois anos -- antes disto ele havia entrado em erupção em 920 e em 1612) o vulcão Eyafjallajökull (que, em tradução literal do islandês, significa glaciar de montanha islandesa), situado em uma das menores calotas glaciais da Islândia, entrou em atividade há cerca de um mês e desde então vem infernizando a vida dos europeus e de milhares de pessoas de outras partes do mundo. Além dos efeitos imediatos sobre o tráfego aéreo na Europa, com prejuízos de bilhões de euros, não se tem ainda noção exata de seus danos sobre o clima e o meio ambiente como um todo, a médio e longo prazos.

O artigo abaixo, publicado no Wall Street Journal de 16/4/2010, faz uma boa síntese sobre o assunto.

Friday, April 16, 2010.

A Natural Event, With Extreme Global Consequence
By GAUTAM NAIK

The eruption of a volcano in Iceland is a stark reminder of how these dramatic events can affect people and places thousands of miles from the actual explosion and, in some cases, for years to come.

Some of the biggest eruptions have killed thousands of people who got caught in their lava flow. Other eruptions have caused acid rain, depleted the earth's ozone layer and even temporarily cooled the planet.

The event in Iceland is relatively small—but if the eruptions continue, the effects could get worse.

Though Iceland has plenty of volcanoes, few actually erupt. The current one started to show worrisome levels of activity around March 21, spewing out gases and ash. Flash-flood risks have forced hundreds of people to flee from near the glacier.

Volcanic ash isn't really ash; it is composed of tiny bits of jagged rock and glass. It is hard and abrasive; it doesn't dissolve in water, and can be spread by the wind.

Ash from the Icelandic eruption was picked up by winds accompanying the Gulf Stream.

Winds at a height of between 30,000 to 36,000 feet—just below the cruising elevation for jets—then carried the ash toward the U.K. and elsewhere in Europe.

If the volcano continues to erupt, and if its ash has a high proportion of sulfur, it can mix with the water vapor in the air and form a weak broth of sulfuric acid, coming down as acid rain.

"But it's hard to say whether that's a problem right now," said Robert Trombley, a former Air Force pilot and now director and of the International Volcano Research Centre, a private organization in Apache Junction, Ariz., which monitors the activity of more than 500 volcanoes every day.

While a large-scale eruption may last only a few days, the tremendous outpouring of gas and ash can have a long-term impact on the climate.

In what is known as the "haze effect," the sulfuric gas gets converted into sulfate aerosols—extremely tiny droplets that reflect more of the incoming solar radiation back into space, thus cooling the lower atmosphere.

There's a countervailing effect, too. Because volcano-produced aerosols can absorb terrestrial radiation, they can act in the opposite manner, to raise the temperature. Both the cooling and warming outcomes can last for several years.

Scientists often find it easier to predict a volcanic eruption, based on certain tell-tale signs, than an earthquake.

There was little warning, however, from under Iceland's Eyjafjallajokull glacier, where the volcano came to life last month after being dormant for nearly 200 years.