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The question comes up nearly every time people are hit with an unusual flood, drought or heatwave. Just last week, researchers reported that the cap of ice that covers most of the Arctic Ocean is 20% smaller than usual for this time of year. Is global warming at work here too?
Climate scientists agree that our world is getting warmer. Nine of the 10 warmest years on record have been in the past decade. Of course, nature has brought about dramatic changes in the earth's climate in the past, such as the Ice Age. But scientists are convinced that this warming trend is being pushed by humans.
|  Traffic in the Walnut, California area burns fossil fuel, clogs highways and pollutes the atmosphere. |
Manmade Climate?
The atmosphere naturally traps heat from the sun, much like a glass greenhouse warms the air inside even when temperatures outside are cool. This "greenhouse effect" makes life possible on our planet.
But people are intensifying the natural greenhouse effect. Enormous amounts of polluting gases are produced when we burn fossil fuels such as coal and oil to produce power for our cities, factories and cars and to heat our homes.
By pumping more and more of these gases into the atmosphere, humans are turning up the thermostat. And the effects have clearly started, according Kevin Trenberth of the National Center for Atmo-spheric Research. "We are already seeing fewer frost days, heavier rains and more droughts and heatwaves," Trenberth told TFK.
Scientists fear that the situation could get much worse. Higher temperatures could affect where important crops such as wheat and corn can be grown. Countless species of plants and animals could face big disturbances of their habitat, and that could mean extinction for polar bears and other animals. Scientists also worry that if mountaintop glaciers and the ice sheets in the Arctic and Antarctic continue to melt, sea levels around the globe will rise. Water would swallow coasts and low-lying islands, where hundreds of millions of people live.
What can be done?
The best chance to slow global warming is to reduce the amount of greenhouse gases that are put into the atmosphere. Most of the world's countries have signed a treaty called the Kyoto Protocol, which requires them to pledge to reduce their greenhouse emissions. But the U.S. has not. President George W. Bush has been sharply criticized for this, but he says it would be too costly for U.S. companies to meet the emission limits.
One thing is certain. Efforts to turn down the heat will have to involve the entire world if they are to succeed. "Climate change is truly a global issue," says Trenberth, "and one that may prove to be humanity's greatest challenge."