This is the 41st anniversary of the first Earth Day, observed in the United States in the aftermath of a disastrous oil spill off the country's West Coast. Earth Day is now celebrated in one form or another in nearly 200 countries.

    This year, Earth Day organizers called on people worldwide to pledge “a billion acts of green” to improve the planet's environmental health.

    As Friday began, organizers calculated that more than 100 million people had already made promises to improve the environment. Those pledges ranged from individuals' plans to reduce the use of toxic chemicals, to switching to compact fluorescent lights at home, to using mass transit for travel to work and eating locally grown food.

    U.S. President Barack Obama said the day is a chance to “renew America's commitment” to environmental protection, and to ensure that American leadership “will continue to be pivotal” in confronting global environmental challenges.

    U.S. first lady Michelle Obama had planned to help work on the habitat at an urban park in Washington, but the event was canceled as rain fell in the capital city. Public officials around the U.S. planned other events, such as in Baltimore, where the governor of the state of Maryland opened an electric-vehicle charging station at an airport.

    Much has changed in the U.S. since the first Earth Day in 1970 – a time when many factories still were allowed to belch smoke and pollutants into the air, and all cars burned fuel containing lead, a dangerous automobile-exhaust pollutant. Over the following decades the nation's Environmental Protection Agency was established, and federal and local jurisdictions enacted many laws protecting air and water supplies and endangered species of animals and plants.

    Environmental regulations nevertheless still cause controversy in some parts of the U.S. The two main political parties, Democrats and Republicans, frequently contest each other's claims about the effect of greenhouse-gas emissions on the warming of the planet. As the nation has struggled to recover from the worst economic downturn in 70 years, some have questioned whether environmental laws contributed to the loss of jobs and whether the resulting rise in energy costs is worthwhile.

    With more than 13 million Americans still jobless, many U.S. consumers have hesitated to purchase higher-priced “environmentally friendly” products. A recent survey has shown that consumers are not buying as many “green” products, such as cleaning supplies for household use, as they did several years ago.(本文由在线英语听力室整理编辑)