Last week’s heat wave wasn’t an anomaly: The first half of 2010 was the warmest January through June on record. The average temperature in that time span was 57.5 degrees Fahrenheit, according to the National Climatic Data Center, whose records go back to 1880. That’s 1.22 F above the 20th-century average. The previous record for the hottest first half of the year was in 1998; 2005 has the record for the hottest whole year.