Global warming: many scientists agree that earth's climate has warmed in recent years. But not all of them think it is a cause for concern.

If you want to see the glaciers (huge masses of ice) that gave Glacier National Park its name, don't wait too long. When President William Howard Taft made the Montana area a national park in 1910, there were about 150 of the massive ice forms. That number has since melted away to around 20.

"The ones that remain are shrinking," says Dan Fagre (FAYgree), a scientist with the U.S. Geological Survey. "We're literally watching glaciers disappear before our eyes." Fagre predicts that most, if not all, of the park's remaining glaciers will be gone within 30 years.

Scientists around the world agree that our planet is getting warmer. Flowers bloom earlier in the spring. Warm-weather plants, insects, birds, and other animals are migrating to once-cooler regions. Average global temperatures have risen over the last 50 years. And, scientists say, the thick ice cap covering the North Pole is melting.

"It's here. It's real," says Tim Barnett about global warming. Barnett is a climatologist at the Scripps Institution of Oceanography in California. "Among [most] scientists, there's no question that this is what's happening--and it's going to affect every single person on Earth."

The Greenhouse Effect 

Over millions of years, Earth's climate has shifted between warmer and cooler temperatures many, many times. Is the current warming trend part of this natural cycle, or something more?

Many scientists think that it is something more. At least part of the warming, they say, is due to pollution created by humans. Common activities, such as burning fossil fuels--oil, gas, and coal--give off carbon dioxide (C[O.sub.2]) and other gases. Most of the burning results from cars, factories, and the power plants that provide energy for houses and office buildings. These gases stay in the atmosphere, intensifying Earth's natural "greenhouse effect."

What is the greenhouse effect? Imagine the inside of a car on a sunny day. Sunlight comes in through the windows (as it does through Earth's atmosphere). The light gets trapped inside the car, heating the interior. If a window is open, some of the heat escapes, but it still remains warm inside the car. If all the windows are shut, however, the heat builds up. The seats and the air inside the car get much hotter.

Earth's atmosphere naturally creates a greenhouse effect, which is what helps make life on Earth possible. Without the atmosphere, much of the sun's energy would bounce back into space, and Earth's surface would be too cold to support life. But many climatologists think that gases from human pollution are, in effect, closing the windows. As more heat energy is trapped inside the atmosphere, global temperatures rise.

Scientists have found that the rise in global temperatures matches the rise in C[O.sub.2] levels in Earth's atmosphere. There may already be enough C[O.sub.2] in the atmosphere to keep warming the planet for decades to come. Computer models predict that Earth's temperatures may rise an additional 2.5 to 10.4 degrees Fahrenheit in the next 100 years.

Should We Worry?

If Earth really is getting warmer, should we be concerned? Most experts agree that human activity is affecting global temperatures. But they are split about whether this poses a serious threat.

John Christy, director of the Earth System Science Center at the University of Alabama at Huntsville, believes that the projected rise in temperatures will not be dramatic enough to cause serious problems. "Most of the predictions are too alarmist," he says.

Patrick J. Michaels, a climatologist for the state of Virginia, agrees. "The fact of the matter is," he says, "if you look at those temperature records that [people] keep on citing, you will see that almost all of the warming takes place in the absolute coldest, most miserable air masses in Siberia and northwestern North America.... We've warmed Siberia from minus 40 [degrees Fahrenheit] to minus 38. Big deal."

Other experts, however, say that it is a big deal. Global temperatures just a few degrees warmer could alter weather patterns and sea levels, and lead to flooding, drought, a rise in the number of damaging storms, and the spread of mosquito-borne diseases.

Glacial melt raises another concern. Much of the world's population relies on glaciers for water to drink and to irrigate crops. "In places like the Himalayas [a mountain range in Asia], the summer water supply is 100 percent glacier meltwater," says Fagre. "But those glaciers may be gone by 2030."

The New York Times reported on another disturbing trend in January. Scientists in Antarctica have found that rising temperatures in some areas there have caused glaciers to thin and ice shelves the size of some U.S. states to disintegrate or recede. On the Antarctic Peninsula, grass is appearing in places that were once hidden under a blanket of ice and snow.

"The evidence is piling up; everything fits," Robert Thomas, a glaciologist from NASA, told the Times. "Around the Amundsen Sea, we have surveyed a half dozen glaciers. All are thinning, in some cases quite rapidly, and in each case, the ice shelf is also thinning."

What are the implications of this? If enough glaciers, which rest on land, slide into the sea, the increase in ocean volume could raise the global sea level.

"If Antarctica collapses, it will have a major effect on the whole globe," said Eric Rignot, a glaciologist at NASA's Jet Propulsion Laboratory in Pasadena, California.

Kyoto Protocol

Many scientists, as well as world leaders, believe that we should take immediate steps to reduce greenhouse-gas emissions. Building cleaner power plants, driving cars that pollute less, and developing new fuels are some proposals for doing so. About 120 countries have signed an international agreement called the Kyoto Protocol. After years of negotiations, the treaty took effect on February 16, 2005. It calls for countries to take immediate steps to reduce the release of C[O.sub.2] and five other gases into the atmosphere.

The United States participated in early negotiations on the treaty, but President George W. Bush ordered a withdrawal from the talks in 2001. Since the agreement does not place restrictions on developing countries, the President argued, it puts undue pressure on industrialized nations. Australia has also refused to ratify (approve) the treaty.

The debate about global warming is likely to continue as your generation comes of age. Today's kids, says Tim Barnett, "should learn about the climate and how it's changing. They should have a say about the world they're going to inherit."

Words to Know

* climatologist: a scientist who studies Earth's long-term climate as well as trends and changes that may affect it.

* emission: something discharged or sent into the air.

Your Turn

THINK ABOUT IT

1. What are some examples of fossil fuels?

2. Do you think that global warming is something to worry about now, sometime in the future, or not al all? Explain.

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* OBJECTIVE

Students should understand

* global warming is a term that describes the increase in Earth's temperature, which is the result of natural and human factors.

* TEACHING STRATEGY

Instruct students to discuss the economic, social, environmental, and political changes that might result from global warming. How would their community be affected by the ongoing rise in Earth's temperature?

* BACKGROUND

A 2003 study by the World Health Organization said that continued global warming would lead to a worldwide increase of malnutrition and mosquito-borne diseases, such as malaria. A team of researchers recently ranked Finland, Norway, Uruguay, Sweden, and Iceland as the five most successful nations at managing development and maintaining "environmental sustainability." The U.S. ranked 45th of the 146 countries studied.

* CRITICAL THINKING

MAIN IDEA: What do scientists say about global warming? (Some scientists believe the increase is a strictly natural occurrence, as Earth's climate has changed many times over the course of the planet's history. Others, however, believe that pollution created by humans has contributed alarmingly to the warming trend.)

COMPREHENSION: Why did President Bush refuse to include the U.S. in the UN's Kyoto Protocol? (President Bush said that the restrictions set by the environmental treaty would place undue burdens on industrialized nations.)

* ACTIVITY

ECO-FRIENDLY TECHNOLOGY: How has modern technology contributed to global warming? What eco-friendly products, such as hybrid automobiles and recyclable plastics and metals, are being manufactured to help reduce pollution? Instruct students to create a consumer guide of environmentally friendly technology.

STANDARDS

SOCIAL STUDIES, GRADES 5-8

* People, places, and environment: How global warming could have severe environmental, political, social, and economic consequences.

* Production, distribution, and consumption: How the consumption of fossil fuels has led to an increase in the emission of pollutants, which is believed to cause global warming.

RESOURCES

PRINT

* Brown, Paul, Global Pollution (Raintree Pub., 2003). Grades 5-8.

* Pringle, Laurence, Global Warming: The Threat of Earth's Changing Climate (Seastar Books, 2003). Grades 5-8.

WEB SITES

* EPA (kids' site) epa.gov/globalwarming/kids

* Global Warming-FAQs www.ncdc.noaa.gov/oa/climate/globalwarming.html

ENVIRONMENT: GLOBAL WARMING, PAGES 5-7

* Decide whether each sentence is true, false, or an opinion. Rewrite a correct version of any false statement on a separate sheet of paper.

--6. Global warming is affecting only the glaciers and ice formations in the North Pole.

--7. The Kyoto Protocol goes into effect in February 2006.

--8. Evidence that Earth's climate has changed includes the appearance of warm-weather plants in once-cooler regions.

--9. Many of the predicted changes resulting from global warming are too alarmist.

--10. President Bush says that the Kyoto Protocol unfairly burdens industrialized nations.

6. False; Global warming is causing environmental changes all over the world.

7. False; The Kyoto Protocol went into effect on February 16, 2005.

8. True

9. Opinion

10. True