Guardian: Since consistent record-keeping began in 1895, the average temperature in the United States has increased by 1.3 to 1.9 degrees Fahrenheit (0.8 to 1.1° Celsius), and most of that change has happened since 1970. The warmest year on record for the United States was 2012. The map above shows temperature changes between 1991 and 2012 compared to the average temperature between 1901 and 1960.