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variations. The drought that struck almost two-thirds of the nation and a La Nina weather event helped push temperatures higher, along with climate change from man-made greenhouse gas emissions, said Katharine Hayhoe, director of the Climate Science Center at Texas Tech University. She said temperature increases are happening faster than scientists predicted.
• "These records do not occur like this in an unchanging climate," said Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in Boulder, Colo. "And they are costing many billions of dollars."
• Global warming is caused by the burning of fossil fuels -- coal, oil and natural gas -- which sends heat-trapping gases, such as carbon dioxide, into the air, changing the climate, scientists say.
• What's happening with temperatures in the United States is consistent with the long-term pattern of "big heat events that reach into new levels of intensity," Arndt said.
• Last year was 3.2 degrees warmer than the average for the entire 20th century. Last July was the hottest month on record. Nineteen states set yearly heat records in 2012, though Alaska was cooler than average.
• U.S. temperature records go back to 1895 and the yearly average is based on reports from more than 1,200 weather stations across the Lower 48 states.
• Several environmental groups, including the World Wildlife Fund, took the opportunity to call on the Obama Administration to do more to fight climate change.
• According to the National Oceanic and Atmospheric Administration, 2012 also had the second-most weather extremes on record after hurricane-heavy 1998, based on a complex mathematical formula that includes temperature records, drought, downpours, and land-falling hurricanes.
• Measured by the number of high-damage events, 2012 ranked second after 2011, with 11 different disasters that caused more than $1 billion in damage, including Superstorm Sandy and the drought, NOAA said.
• The drought was the worst since the 1950s and slightly behind the Dust Bowl of the 1930s, meteorologists said. During a drought, the ground is so dry that there's not enough moisture in the soil to evaporate into the atmosphere to cause rainfall, which leads to hotter, drier air. This was fed in the U.S. by La Nina, which is linked to drought.
• Scientists say even with global warming, natural and local weather changes mean that temperatures will go up and down over the years. But overall, temperatures are climbing. In the United States, the temperature trend has gone up 1.3 degrees over the last century, according to NOAA data. The last year the U.S. was

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