Nine of the warmest years were recorded in the 21st century; 1998 is the only 20th century entry in the ranking. NASA said that the average temperature around the globe in 2011 was 0.92 degrees F (0.51 C) warmer than the mid-20th century baseline. The difference between 2011 and 2010, the warmest year on GISS record, was 0.22 degrees F (0.12 C).
"We know the planet is absorbing more energy than it is emitting," said GISS Director James Hansen in a prepared statement. "So we are continuing to see a trend toward higher temperatures. Even with the cooling effects of a strong La Niña influence and low solar activity for the past several years, 2011 was one of the 10 warmest years on record."
The increasing level of greenhouse gases is blamed for the an ongoing temperature increases, which NASA says may vary from year to year, but will continue to climb in the future on average. GISS noted that the carbon dioxide concentration in the atmosphere was about 285 parts per million in 1880, about 315 parts per million in 1960 and is above 390 parts per million today. Hansen said he expects record-breaking global average temperature in the next two to three years because of increasing solar activity and the "next El Niño will increase tropical Pacific temperatures".