Week of 12/04/2005

Dear EarthTalk: What are the implications of the increased breakup of Antarctica's large floating ice shelves in recent years?

—Gaertner Olivier, Brussels, Belgium

Ice shelves are thick plates of ice that float on the ocean around much of Antarctica. Snow, glaciers and ice floes feed these large plates in the colder months. In warmer periods, surface melting creates standing water that leaks into cracks and speeds the breaking off (calving) of icebergs, decreasing the continent's mass in a natural cycle as old as Antarctica itself.

"Large icebergs calve off on a fairly regular basis from the larger ice shelves in Antarctica," says Dr. Ted Scambos, a research associate at National Snow and Ice Data Center. "This is a part of their normal evolution."

The only effect of such calving that scientists are sure about is that they are changing the outline of Antarctica. The break-up of the ice shelves, which account for about two percent of the continent's landmass, does not have any measurable effect on sea levels. "Since an iceberg floats in ocean water, and much of it is below the surface, it is already displacing the same volume of water it will contribute when it eventually melts," Scambos explains.

But while such calving activity may not be new, it has increased over the last 30 years, with larger and larger chunks breaking off from Antarctica where they float free in the ocean and break up into successively smaller pieces. One especially large iceberg, a chunk the size and shape of New York's Long Island and dubbed "B15A" by researchers, broke off from Antarctica's Ross Ice Shelf in 2000 and just last April collided with the continent's Drygalski Ice Tongue (a long shelf of ice extending out to sea from the mainland). The iceberg itself remained intact, but a city-sized chunk of the ice tongue broke off and is now floating free.

Most researchers suspect that recent increases in calving are linked to warming surface air temperatures as a result of human-induced climate change. British glaciologist David Vaughan says, "There is no doubt that the climate on the Antarctic Peninsula has warmed significantly over the last few decades. What we're seeing now are changes only just working through to glaciers and ice sheets." Scambos says that, as Antarctic summer temperatures continue to increase, the process can be expected to become more widespread, and could begin to significantly increase sea levels around the world.

Even a relatively small rise in sea level would make some densely settled coastal areas uninhabitable. The Intergovernmental Panel on Climate Change, an international group of climatologists, predicts a global sea level rise of less than three feet by 2100, but also warns that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea levels many more feet in coming centuries. Some 200 million people inhabit low-lying areas in countries like Vietnam, Bangladesh, China, India and The Philippines and could be displaced, leading to a major international refugee crisis.

CONTACTS: Intergovernmental Panel on Climate Change, www.ipcc.ch, NASA's iceberg collision page, www.nasa.gov/vision/earth/lookingatearth/Iceberg_collides.html.


Dear EarthTalk: Are there any environmentally friendly alternatives to aerosol spray dusters?

—Troy Blakely, New York, NY

Artists, photographers and electronics technicians have long relied on aerosol spray dusters to carefully remove dust and fine particles from sensitive surfaces like paintings, film and computer hardware. An aerosol spray uses a propellant chemical, along with various other additives, to push clean air or a particular active ingredient out of the container. Until the late-1980s, chlorofluorocarbons (CFCs) were the primary propellants used. However, CFCs were phased out worldwide after scientists discovered that they were helping to deplete the Earth's ozone layer.

While makers of aerosol spray dusters don't use CFCs anymore, they can put other potentially harmful hydrocarbons, such as methylene chloride, into their products. The Consumer Federation of America reports that many of the highly flammable substances used are carcinogenic. Some are also neurotoxic (harmful to nerve tissue) and contain chemicals that can damage one's sense of smell.

Hydrocarbon-free alternatives are not that easy to come by, though one manufacturer, Advantus, makes a line of nontoxic, chemical-free and "ozone-safe" dusters for home and office. Some are refillable and are thus waste saving, too, and can be ordered from the company's website. Several other companies, including Universal and Falcon, make spray dusters that use Earth-friendly propellants, but they are not chemical-free. Most are available at most office supply stores or online at CleanSweepSupply.com.

Those who rely on spray dusters can minimize their use by keeping the indoor environment as dust-free as possible. Frequent damp dusting and vacuuming are the best defenses against a dusty indoor environment. Clutter consisting of small objects and books make dusting more difficult—and all the more necessary. Routine air duct cleaning and frequent changing of furnace and air conditioning filters will also minimize the accumulation of dust in both homes and offices.

CONTACTS: Consumer Federation of America, www.consumerfed.org, Advantus Corp., www.advantus.com; CleanSweepSupply.com, www.cleansweepsupply.com.