New satellite images suggest that the Earth is getting dustier. Well, not necessarily, chimed in Dan Muhs of the U.S. Geological Survey. Scientists increasingly turn to satellite images to track dust plumes in the atmosphere.
“The ability to monitor dust plumes is better now than in the past. This new information gives us a better appreciation of atmospheric dust,” said Muhs.
And it is important to study dust, because it is, in the words of Karen Kohfeld of Simon Fraser University, Burnaby Canada, the great communicator of the Earth System. “Dust links the land, air and sea system,” said Kohfeld.
During a news briefing at the AAAS annual meeting in San Diego, Calif, a panel of climate experts converged to discuss the impact of dust in the atmosphere. Scientists have been monitoring dust in the atmosphere using satellites since the 1990s. The dust arrives on American shores from three locations — North African and Middle East desert-derived dust affects the southern United States and Caribbean; Pacific loess deposits affect the western United States and Canada; and Arctic loess deposits affect to the northern Canada, United States, and northern Europe.
The last source is the real surprise to scientists.
Glaciers in the Arctic have been retreating for decades as the planet continues to warm. According to Joseph Prospero of the University of Miami, “Our recent work in Iceland has shown that most of the dust events there are associated with dust emitted from glacial outwash deposits, which may be carried to northern latitudes and into Europe by synoptic weather events.”
The trend toward glacial shrinkage is not expected to slow in the near future, leaving the scientific community to ponder how this new addition of dust will affect the planet and human health.
Now what exactly is dust? According to the panel, dust is composed of soil particles (primarily mineral material) smaller than 50 micron (4 × 10-4 in) in diameter — the thickness of an average human hair.
“Not taking into account human created industrial particles produced during combustion, aerosols are dominated by dust and sea salt,” said Natalie Mahowal of Cornell University. “These particles range between 2 to 20 microns,” stated Muhs. According to Muhs, ten percent of the planet is covered with loess deposits, a rock flour produced by glacial grinding of rocks, and this material is a strong contributor to global dust.
The interest in atmospheric dust is based on how these tiny particles can affect climate, precipitation, and human health.
Dust is a rouge element in the climate system. It can behave as an agent causing the planet to warm or cool depending on its location in the atmosphere. High in the atmosphere, dust acts like tiny mirrors reflecting the incoming solar radiation back into space resulting in a net cooling effect. However, if the dust is located lower in the atmosphere, at a height of the clouds, the dark color of the dust helps to absorb incoming solar radiation resulting in a net warming effect. This duel nature of dust has frustrated climate modelers who develop computer models to make predictions of future climate conditions.
In addition to warming and cooling, dust also wrecks havoc with the formation of rain. Dust particles act like tiny vehicles that water vapor condenses onto to form rain droplets. When there are too many dust particles in the atmosphere the rain droplets cannot grow. Think of this in terms of the winnings of the lottery. When there are only five winners of a jackpot, everyone gets a big payout, but when there are hundreds of winners, each person walks away from the game with some change in their pocket. This is similar to how excess dust affects precipitation formation.
“The first 30 years of the dust record showed a strong relationship between dust transport across the ocean to rainfall amounts in the Sahel and Soudan regions of Africa,” said Prospero. “It’s important to note that the level of dust transport is not necessarily related directly to rainfall but possibly to other climate factors associated with the variability of rainfall.”
In addition, exposure to high concentrations of aerosols, especially particles smaller than 2 microns in diameter, have been linked to adverse health effects including asthma, coronary disease, and cancer.
Dust is not only a driver of climate change, but an archive of changes in climate. “We still have work to do to understand the fundamental processes and relationship between climate, rainfall, and dust transport,” says Propero. “Predicting long-term effects of climate and dust transport is exacerbated by the fact that many of the climate prediction models for lower latitude Africa are not consistent.”
EarthSpin 