Thursday, November 23, 2006
Volcano eruptions in Iceland are responsible for the famine in Africa
A series of 10 eruptions from the Laki Craters changed atmospheric conditions in most of the Northern Hemisphere and led to unusual temperature and precipitation patterns that peaked in the summer of 1783, causing below normal rainfall in most of the Nile drainage basin and record low levels for up to one year following the eruptions.
"Some of the driest weather occurred over the Nile and Niger River watersheds," explained lead author Luke Oman, a researcher from Rutgers University, NJ. "The relative lack of cloud cover and increased temperature likely amplified evaporation, further lessening water available for run-off."
Large amounts of sulfur dioxide are released into the atmosphere when volcanic eruptions takes place. Aerosol particles, which reflect sunlight back into space, form when this gas combines with water vapor. The result is cooler average temperatures on Earth.
Researchers used computer models to simulate how Iceland's Laki eruptions affected temperature and rainfall levels over the Sahel, a stretch h of land from the Atlantic ocean to the "Horn of Africa."
"These findings may help us improve our predictions of climate response following the next strong high-latitude eruption, specifically concerning changes in temperature and precipitation," Oman said. "Many societies are very dependent on seasonal precipitation for their livelihoods, and these predictions may ultimately allow communities time to plan for consequences, including impacts on regional food and water supplies."
Simulations showed that the aerosols formed by the eruptions cooled average temperatures in the Northern Hemisphere by up to 5.4 degrees Fahrenheit. Tree ring data in Alaska and Siberia also showed reduced growth during the same summer, signifying cooler than normal weather.
The unusually cool temperatures reduced the temperature difference between the land masses of Africa and Eurasia and their respective water masses, the Atlantic and Indian oceans. Usually, a sharp contrast in temperature between land and sea creates raging monsoon winds. Monsoons are seasonal shifts in wind direction that signify the beginning of the rainy season.
The lack of monsoons led to a reduction in cloud cover over the Sahel of Africa, southern Arabian Peninsula and India that summer. This caused temperatures to increase by as much as 3.6 degrees Fahrenheit and induced drought in the region. The resulting food shortage reduced the population of the Nile Valley by a sixth.
The study was detailed in the Sept. 30 issue of the American Geophysical Union's Geophysical Research Letters.