Study finds 'alarming' decline in bumblebees; desert dust may melt glaciers
Study finds extreme decline in some species of agriculturally important bees
Four previously abundant species of bumblebee are close to disappearing in the United States, researchers reported last week in a study confirming that the agriculturally important bees are being affected worldwide.
They documented a 96 percent decline in the numbers of the four species - there are 50 species in North America - and said their range had shrunk by as much as 87 percent. As with honeybees, a pathogen is partly involved, but the researchers also found evidence the bees are vulnerable to inbreeding caused by habitat loss.
"We provide incontrovertible evidence that multiple Bombus species have experienced sharp population declines at the national level," the researchers reported in the Proceedings of the National Academy of Sciences, calling the findings "alarming."
"These are one of the most important pollinators of native plants," Sydney Cameron of the University of Illinois at Urbana, said in a telephone interview.
In recent years, experts have documented a disappearance of bees in what is widely called colony collapse disorder, blamed on many factors including parasites, fungi, stress, pesticides and viruses. But most studies have focused on honeybees. Bumblebees are also important pollinators, said Cameron, who led the new study, but they are far less studied. Among the plants pollinated by bumblebees, she said, are cranberries, blueberries and tomatoes.
"This is a wake-up call that bumblebee species are declining not only in Europe, not only in Asia, but also in North America," Cameron said.
Dust from far-off deserts may speed up the melting of glaciers in the Himalayas
Sediments taken from the bottom of a lake on the Tibetan plateau suggest that changes in wind patterns caused by global warming may be making the area dustier. That trend could accelerate the melting of glaciers in the Himalayas and affect already imperiled water supplies.
Jessica Conroy, a graduate student in paleoclimatology at the University of Arizona in Tucson, helped collect sediment cores from the bottom of Tibet's Kiang Lake. The cores track the history of climate in the region back to the year 1050. According to Conroy, the amount of fine-grained dust in the lake sediment increased during the 20th century. Finer dust comes from distant desert regions, suggesting stronger winds.
Scientists have previously attributed the rise of dust in the region to an increase in grazing and other relatively local developments. Conroy's data, presented last month, showed that dusty periods coincide with summers when a Northern Hemisphere atmospheric phenomenon called the Arctic oscillation is in a "positive phase." This phase leads to stronger winds in desert areas north of the lake and south of the Himalayas.
Global warming seems to be keeping the Arctic oscillation in its positive phase more often.
"It's going to continue to be dusty in this region, and dust can accelerate the melting of the glaciers in the Himalayas," Conroy said. That's because the dust lands on the white ice and makes it darker, absorbing radiation and accelerating melting. These glaciers, which provide water for hundreds of millions of people across Asia, are in serious danger. Dust also warms the air above the Tibetan plateau, enhancing monsoon circulation patterns, which could affect rain and alter rainfall patterns across southern Asia.
- Eli Kintisch
This article was produced by ScienceNOW, the daily online news service of the journal Science, and can be read online at www.sciencemag.org .