The graph shows the annual average global surface temperature anomalies since 1950. (The temperature anomaly is the difference between the actual temperature and the average temperature for the period 1950-2010.) The global average surface temperature in 2011 is currently the tenth highest on record and is higher than the global average surface temperature for any previous year with a La Niña event. (A La Niña event has a relative cooling effect. Blue bars indicate years influenced by a La Niña event.) The 13 warmest years have all occurred in the 15 years since 1997. Statistical methods are being developed to quantify the likelihood of extreme events in future years.