A decrease in airborne dust and volcanic emissions has contributed to warming the North Atlantic Ocean in the past three decades, a study showed on Thursday.
About 70 percent of the Atlantic’s warming since 1980, at an average per-decade rate of a half-degree Fahrenheit (a quarter-degree Celsius), was due to less dust blown from African dust storms or to volcanic eruptions, scientists wrote in the journal Science.
“Volcanoes and dust storms are really important if you want to understand (climatic) changes over long periods of time,” said the study’s lead author Amato Evan, a researcher with the University of Wisconsin-Madison.
He said airborne particles producing warmer temperatures can also help cause hurricanes, which thrive on warm water.
Evan and his colleagues had previously shown that African dust and other airborne particles can reduce hurricane activity by allowing less sunlight to reach the water and thus cool the sea surface.
Years with low dust activity, such as 2004 and 2005 — a record-breaking storm year — have been associated with more frequent storms, the researchers noted.
During their study, the researchers used satellite data of dust and other particles along with existing climate models to calculate how much of the Atlantic warming of the past 26 years was due to changes in tropical volcanic activity.
Major such volcanic eruptions that dimmed sunlight were Mexico’s El Chichon in 1982 and Mount Pinatubo in the Philippines in 1991.
Although volcanoes are unpredictable by nature, Evan said newer climate models should at least include dust storms as a factor to predict ocean temperature changes accurately.
“We don’t really understand how dust is going to change in these climate projections, and changes in dust could have a really good effect or a really bad effect,” he said.
The researchers attributed a quarter of the warming to the dust storms themselves and said that only about 30 percent of the temperature increases were due to other factors, such as global warming.
“This makes sense, because we don’t really expect global warming to make the ocean [temperature] increase that fast,” said Evan.
Evan wrote the study with other experts from the University of Wisconsin-Madison and the National Oceanic and Atmospheric Administration.
Source ::: The Daily Star ::: 28 March 2009 (AFP, Washington)