SILENCE IS GOLDEN: Compared with air and water pollution, noise pollution is often dismissed as one of the least serious environmental problems we face. It doesn't expose us to chemical toxins, it doesn't linger after the source goes away, and it's just a matter of degrees, anyway — you can't have civilization without making a little noise. But prolonged exposure to that noise does more than just damage our ear drums and prop up the hearing-aid industry: It has been shown to cause chronic stress in humans, a biological response that our ancestors evolved in the wild, where sudden noises usually signal danger. As the din of society continues to grow louder and wider, Newsweek interviews an audio ecologist who's quietly fighting to save America's few remaining silent places. Scientist and author Gordon Hempton defines true silence as "the complete absence of all audible mechanical vibrations, leaving only the sounds of nature at her most natural." Hempton travels around the globe, recording natural sounds ranging from howling coyotes to melting snow, all while fleeing the invasive racket of traffic, airplanes, snowmobiles and other noisy manmade contraptions. He won't divulge some of his favorite quiet spots for fear of people ruining them, but does offer advice for finding your own: Look at a NASA photo of the United States at night (or check out these nighttime photos of world cities), and head for the dark areas. "Light pollution is the evil cousin of noise pollution," Hempton says. (Sources: Newsweek, British Medical Bulletin, EPA, NASA)

GREENWASHING TERRORISM: Al-Qaeda leader Osama bin Laden reportedly issued a new audiotape Friday, calling for an international boycott of American goods and the U.S. dollar as a way to combat climate change. In the new tape, a voice said to be bin Laden's rambles about the dangers of global warming before predictably segueing into his broader argument — that the only way to stop worldwide catastrophe is to bring "the wheels of the American economy" to a standstill. (Maybe no one has told bin Laden that China is actually now the world's largest emitter of greenhouse gas emissions?) The tape's authenticity has yet to be confirmed, but it wouldn't be the first time bin Laden has mentioned climate change, just his first tape that's dedicated entirely to the subject. The tape blames Western nations for floods, desertification and other environmental ills around the world, and demands "drastic action" rather than "solutions that partially reduce the effect." Bin Laden also released another tape last week in which he took credit for a Nigerian student's failed Christmas Day airplane bombing attempt, and many terrorism experts say these tapes seem to be desperate attempts by bin Laden to regain his relevance on the world stage. (Sources: Associated Press, BBC News)

CUTTING CARBON: The much-maligned Copenhagen Accord received a boost Thursday, when the United States officially pledged what President Obama first suggested last year: The country will cut its greenhouse gas emissions 17 percent from 2005 levels by 2020. The Obama administration submitted this reduction target to the U.N. three days before the Jan. 31 deadline, but it came with an asterisk. Acknowledging that any such cuts hinge on what Congress will allow, the U.S. plan promises to reduce the country's emissions "in the range of 17 percent, in conformity with anticipated U.S. energy and climate legislation, recognizing that the final target will be reported to the Secretariat in light of enacted legislation." In other words, the U.S. will cut emissions by about 17 percent, as long as Congress says that's OK. In the meantime, the Obama administration also announced another major emissions plan on Friday: The U.S. federal government will slash its own carbon emissions 28 percent by 2020, saving an estimated $8 billion to $11 billion in energy costs. "Our goal is to lower costs, reduce pollution, and shift federal energy expenses away from oil and towards local, clean energy," Obama said. (Source: Los Angeles TimesWashington Post)

MAKING TRACKS: President Obama announced $8 billion in stimulus funding on Thursday for 13 high-speed rail corridors, laying the groundwork for a larger, nationwide network that could one day rival President Dwight Eisenhower's interstate highway system. Rail projects in California, Florida and the Midwest were the big winners at Thursday's town-hall meeting in Tampa, Fla., where Obama highlighted the economic benefits of such an investment. "It creates jobs immediately and it lays the foundation for a vibrant economy in the future," he said, adding that when the Tampa-to-Orlando line is finished, "I'm going to come back down here and ride it." In addition to creating jobs and boosting commerce, the new rail networks are expected to reduce traffic congestion, automobile exhaust and greenhouse gas emissions in the regions they interconnect. While all the networks are being called "high-speed," the speeds will vary among the regions — California's trains will exceed 200 mph, others will top out at 110 mph, and some of the slowest new rail lines in Ohio will feature trains that travel no faster than 79 mph. (Source: AP)

GETTING THE VAPORS: Scientists who are curious why the 1990s' rampant global warming hasn't continued its breakneck pace this decade may now have their answer — water vapor. They've long known that vaporized water is a major part of Earth's natural greenhouse gas effect, trapping solar heat in the atmosphere and radiating it back down to the surface. But atmospheric water vapor levels fell after the 1990s, and a new study published in the journal Science suggests this drop-off may have offset the simultaneous rise of humans' greenhouse gas emissions. The decade from 2000-2009 was still the warmest ever recorded worldwide, but global temperatures didn't rise as rapidly as they did during the '90s. The planet should have heated up by 0.25 degree Fahrenheit during the 2000s based on the previous decade's trend, but actually only rose by 0.18 degree, and the researchers say a mysterious decline in water vapor is likely the reason. But what caused such a large drop in water vapor? "We really don't know," says NOAA senior scientist Susan Solomon, lead author of the study and also co-chair of the U.N. Intergovernmental Panel on Climate Change's landmark 2007 report on the effects of global warming. "We don't have enough information yet." (Sources: USA Today, Guardian)

DEFENDING RIGHTS: In an effort to protect endangered right whales from a potential cacophony in their winter breeding grounds, a dozen environmental groups are suing the U.S. Navy over a planned sonar training range off the Southeast coast. Their lawsuit argues that the Navy hasn't fully studied how the sonar might affect the area's noise-sensitive marine mammals, and is asking a federal court to force the Navy to rework its environmental impact assessment for the project. The groups want the Navy to employ seasonal restrictions on the range to safeguard breeding or newborn right whales from being bombarded with sonar, and also want ships to follow the federal "ship strike" rule, with large vessels slowing down to 11.5 mph along the whales' coastal migration routes. The sonar range would be built in northern Florida waters that are a central part of the right whale's winter breeding ground, and are also popular hangouts for other species such as loggerhead sea turtles. "We think there are a lot of things that could have been done better that don't preclude the Navy's ability to do the training it needs to do," an attorney with the Southern Environmental Law Center tells the Charleston (S.C.) Post and Courier. Right whales were nearly wiped out by whale hunters in the 19th century, and with only about 400 left alive today, the species' long-term survival is still considered to be in doubt. (Source: Charleston Post and Courier)

Russell McLendon

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Photo (airplane over house): ZUMA Press

Photo (Osama bin Laden): AP

Photo (coal-fired power plant): ZUMA Press

Photo (Obama in Tampa on Jan. 28): ZUMA Press

Photo (clouds): U.S. National Park Service

Photo (right whale): U.S. Department of the Interior

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.