Week of 9/02/07

Dear EarthTalk: What is the issue with the Gulf Stream in relation to global warming? Could it really stop or disappear altogether? If so, what are the ramifications of this?

—Lynn Eytel, Clark Summit, PA

Part of the Ocean Conveyor Belt—a great river of ocean water that traverses the saltwater sections of the globe—the Gulf Stream stretches from the Gulf of Mexico up the eastern seaboard of the U.S., where it splits, one stream heading for Canada’s Atlantic coast and the other for northern Europe and Greenland. By taking warm water from the equatorial Pacific Ocean and carrying it into the colder North Atlantic, the Gulf Stream warms up the eastern U.S. and northwestern Europe by about five degrees Celsius, making those regions much more hospitable than they would otherwise be.

Among the greatest fears scientists have about global warming is that it will cause the massive ice fields of Greenland and other locales at the northern end of the Gulf Stream to melt rapidly, sending surges of cold water into the ocean system and interrupting the flow of the Ocean Conveyor Belt. One doomsday scenario is that such an event would stop or disrupt the whole Ocean Conveyor Belt system, plunging Western Europe into a new ice age without the benefit of the warmth delivered by the Gulf Stream. "The possibility exists that a disruption of the Atlantic currents might have implications far beyond a colder northwest Europe, perhaps bringing dramatic climatic changes to the entire planet," says Bill McGuire, a geophysical hazards professor at University College London’s Benfield Hazard Research Centre.

Computer models simulating ocean-atmosphere climate dynamics indicate that the North Atlantic region would cool between three and five degrees Celsius if Conveyor circulation were totally disrupted. "It would produce winters twice as cold as the worst winters on record in the eastern United States in the past century," says Woods Hole Oceanographic Institution’s Robert Gagosian.

The slowing of the Gulf Stream has been directly linked with dramatic regional cooling before, says McGuire. "Just 10,000 years ago, during a climatic cold snap known as the Younger Dryas, the current was severely weakened, causing northern European temperatures to fall by as much as 10 degrees Fahrenheit," he says. And 10,000 years earlier—at the height of the last ice age when most of northwestern Europe was a frozen wasteland—the Gulf Stream had just two-thirds of the strength it has now.

A less dramatic prediction sees the Gulf Stream slowing down but not stopping entirely, causing the east coast of North America and northwestern Europe to suffer only minor winter temperature dips. And some scientists even put forth the optimistic hypothesis that the cooling effects of a weakened Gulf Stream could actually help offset the higher temperatures otherwise caused by global warming.

To McGuire, these uncertainties underscore that fact that human-induced global warming is "nothing more nor less than a great planetary experiment, many of the outcomes of which we cannot predict." Whether or not we can trim our addiction to fossil fuels might just be the determining factor in whether global warming wreaks havoc around the world, or just causes us minor annoyances.

CONTACTS: University College London’s Benfield Hazard Research Centre; Woods Hole Oceanographic Institution

Dear EarthTalk: Is it true that anti-bacterial soaps are no better at preventing infections than plain soaps and that they are actually harmful to the environment?

—Avery Bicks, New York, NY

University of Michigan researchers reviewed numerous studies conducted between 1980 and 2006 and concluded that antibacterial soaps that contain triclosan as the main active ingredient are no better at preventing infections than plain soaps. Further, the team argued that these antibacterial soaps could actually pose a health risk, because they may kill beneficial bacteria and also reduce the effectiveness of some common antibiotics, such as amoxicillin. The study was published in the August 2007 issue of the peer-reviewed journal, Clinical Infectious Diseases.

These findings concur with earlier research conducted by Tufts University’s Alliance for the Prudent Use of Antibiotics. The Tufts study concluded that overuse of triclosan could cause new strains of bacteria to develop, thus "changing the kind of bacteria in our houses to those that may actually be harmful or resistant to antibiotics
" said Tufts" Dr. Stuart Levy.

According to the non-profit group Beyond Pesticides, laboratory studies have found a number of different strains of mutated bacteria that are resistant to triclosan and to certain antibiotics. The organization also cites reports of triclosan converting into a carcinogenic class of chemicals known as dioxins when exposed to water and ultraviolet radiation. Besides cancer, dioxins have been linked to weakening of the human immune system, decreased fertility, altered sex hormones and birth defects.

If antibacterial hand soap is not effective at reducing infections, consumers may wonder about whether alcohol-based hand sanitizers may do a better job. Combing through different studies on the topic yields mixed conclusions. According to one study conducted at Colorado State University, alcohol-based hand sanitizers were as much as twice as effective as either regular soap or antibacterial soap at reducing germs on human hands.

A Purdue University study, however, contradicts these findings, concluding that while alcohol-based hand sanitizers may kill more germs than plain or triclosan-based soaps, they do not prevent more infections that make people sick. Instead they may kill the human body’s own beneficial bacteria by stripping the skin of its outer layer of oil.

The best advice might just come from a study published in the journal Dairy, Food and Environmental Sanitation back in 1998, which concluded that washing hands thoroughly for 20 seconds or more with plain soap and warm water is by far the most effective way to reduce harmful bacteria, and as such remains our best defense against getting sick.

CONTACTS: Clinical Infectious Diseases; Tufts" Alliance for the Prudent Use of Antibiotics; Beyond Pesticides

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