30 years of above average temperatures means the climate has changed

If you’re younger than 30, you’ve never experienced a month in which the average surface temperature of the Earth was below average. Each month, the US National Climatic Data Center calculates Earth’s average surface temperature using temperature measurements that cover the Earth’s surface. Then, another average is calculated for each month of the year for the twentieth century, 1901-2000. For each month, this gives one number representative of the entire century. Subtract this overall 1900s monthly average – which for February is 53.9F (12.1C) – from each individual month’s temperature and you’ve got the anomaly: that is, the difference from the average.
The last month that was at or below that 1900s average was February 1985. Ronald Reagan had just started his second presidential term and Foreigner had the number one single with “I want to know what love is.”These temperature observations make it clear the new normal will be systematically rising temperatures, not the stability of the last 100 years. The traditional definition of climate is the 30-year average of weather. The fact that – once the official records are in for February 2015 – it will have been 30 years since a month was below average is an important measure that the climate has changed.
Link:http://www.wunderground.com/blog/RickyRood/comment.html?entrynum=329#commenttop