USA Today: Despite an unusually chilly year in the Midwest, the national U.S. temperature was slightly above average in 2009, according to the National Climatic Data Center. This marked the 13th consecutive year the nation experienced a warmer-than-normal average temperature. Since the late 1980s, 21 of the last 24 years have been unusually warm in the USA. Beginning in late 1800s, when accurate weather records began, the country has been warming at a rate of about 0.1 degree per decade, …