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Less clouds, more haze for China
Augustine ash
Highlighting landslide risk

Less clouds, more haze for China

China has had fewer days with cloud cover over the past half-century, according to new weather station data. At the same time, however, the region has cooled and evaporation has decreased — suggesting instead the presence of more clouds, which reflect solar rays and their heat. Researchers analyzing the new data speculate that increases in pollution may be the culprit behind the paradox.

A team led by Yun Qian of the Pacific Northwest National Laboratory in Richland, Wash., looked at data taken from 1955 to 2000 from 537 weather stations scattered across China. They determined that on average, differences between night and day temperatures and the amount and duration of sunshine in China had decreased around 2 percent every decade, which would suggest an increasing trend in cloud cover. But, the team wrote in Geophysical Research Letters on Jan. 11, human and satellite observations told a different story: Cloud cover decreased slightly over that time period. Haze remained, however, measured by the stations as overcast days.

China’s emissions of aerosol particles that create haze increased until the mid-1990s, according to state records, and have seemed to level out since then. Aerosol particles have properties that allow them to both scatter and absorb solar radiation, depending on whether they are made of sulfate (which reflects it) or soot (black carbon, which absorbs it). The “mismatch” between cooling and increased smog, the team says, “reminds us of the complexity of aerosol composition and mixing.”

In this case, the haze seems to have reflected more solar radiation, preventing it from reaching the ground. Less heat on the ground would decrease the evaporation of soil moisture, which contributes to cloud formation.

“The key in this case was the fact that the cloud fraction was decreasing simultaneously with solar radiation,” which gives the new report a “unique angle” on describing aerosols over China, says Mark Jacobson, an atmospheric scientist at Stanford University in Palo Alto, Calif. Jacobson hazards his own guess as to why aerosols might be further reducing solar radiation in the area: As the particles absorb heat in the atmosphere, the warmer temperatures keep water from depositing on clouds, as relative humidity increases. This lack of water leads to smaller spread out clouds — in effect, blocking more solar radiation.

Despite their speculation that smog is responsible, the researchers wrote that people “cannot expect a simple correspondence between pollutant emissions and solar radiation on annual or even decadal timescales.” Still, Qian says that smoggy regions experienced a slight cooling effect, noting that the particle pollutants possibly offset the background temperature signals from global warming. “The emission issue is very difficult to predict,” he says, depending on China’s future coal use and energy production, as well as environmental protection policies and the adoption of sulfur emission controls.

The research is “a very clever study showing the impact of increased aerosol air pollution on climate in China — simple measurements showing profound effects,” says Russell Dickerson of the University of Maryland in College Park, with results consistent with satellite observations and past studies. Dickerson says that particulate matter in the atmosphere “probably [has] large-scale impacts” on chemistry and air quality. He sees the work as support for a “call for action to implement methods for sustainable development in Asian industry, transportation and agriculture.”

Naomi Lubick

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Augustine ash

Alaska’s Augustine Volcano made headlines in January by erupting for the first time in almost 20 years. Starting in December, earthquake activity ramped up in the volcano, situated in southwestern Cook Inlet, triggering closer monitoring by the Alaska Volcano Observatory. In mid-January, Augustine eventually shot ash plumes into the air up to 8 kilometers (5 miles) high, drifting over the Kenai Peninsula, about 100 kilometers away. And on Jan. 30, the volcano spewed pyroclastic flows, as well as steam with minor amounts of ash in a plume that extended to the northeast (shown here with a viewpoint from the southwest Print Exclusive). The drifting ash temporarily grounded flights from Kodiak Island.

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Highlighting landslide risk

More than 91,900 people died in 2005 because of natural disasters, according to data released by the United Nations in January. Of those, more than 80,000 died in the earthquake that shook Pakistan on Oct. 8 and its ensuing landslides. Landslides, alone or in conjunction with earthquakes and volcanic activity, are often unrecognized as a serious threat, scientists say.

“On an annual basis, there are many, many instances of small damaging landslides,” says Anthony Crone of the U.S. Geological Survey in Boulder, Colo., and “they have a cumulative effect” leading to large financial losses, but they get little public attention.

At a meeting in Tokyo in January, researchers from the United Nations University presented data to diplomats and international organizations showing that nearly 500 historic landslides from 1903 to 2004 displaced, killed or otherwise affected more than 10 million people and inflicted billions of dollars of damage.

Although Asia has the most landslides, the most deaths and injuries occur from events in the Americas (see Geotimes, December 2005). Other places of concern cited at the meeting — intended to raise awareness and give researchers and countries an agenda of priorities — include World Heritage cultural sites, such as Incan ruins at Machu Picchu, where tourists were stranded last year after landslides blocked the only path out.

“Landslide risk reduction is a young science that has a large number of questions to answer,” says Srikantha Herath, a professor at the United Nations University and Institute of Industrial Science at the University of Tokyo, who participated in the meeting. In addition to improving science and mitigation efforts, Crone also suggests limiting where people can build, in much the same way that floodplains in some regions are legally off limits for housing or other permanent infrastructure.

“As the world’s population increases, people tend to be moving into more hazardous locations,” he says. “Landslides are just one in the suite of natural hazards that need to be addressed and that we all need to be aware of.”

Naomi Lubick

Links:
"Landslides bury Guatemala" and "Quake sets off landslides in Kashmir," Geotimes, December 2005

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