• Global warming is the increase in amounts of "greenhouse gases" in Earth's atmosphere
• Greenhouse gases trap the sun's rays in the atmosphere, raising the temperature to abnormal levels
• The main greenhouse gases are carbon dioxide, water vapor, methane, and ozone
• Greenhouse gases are caused by natural gases and other common sources of energy, as they are released when those sources are burned
• The 1990s were the warmest decades since the thermometer was used to measure temperature.
• 2006 was the warmest year on record for the U.S. according to some sources. Others say it was 2005, 2007, or 1998.
• In the last 1,000 years, the temperature increase in the 20th century has been the largest.
• Over 400,000 square miles of Arctic sea ice have melted.
• In 2005, over $100 billion dollars in damage was caused by hurricanes hitting the U.S. coast.
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