Start tossing your winter coats and buying bikinis. NASA announced this weekend that not only was this September the warmest one on record, but the last six months have been the warmest middle half of a year on record, too. Each month, from April to September, has similarly set the record for hottest of all time. April was particularly warm, and was the first month in 800,000 years where atmospheric carbon dioxide levels hit 400 parts per million.
