Continuing a trend of warming over the past few years, NASA scientists say 2011 was the ninth warmest year in terms of average global temperatures since 1980.
In fact, nine of the 10 warmest years in the modern meteorological record have occurred since the year 2000.
The report was released today (Feb. 24) by NASA's Goddard Institute for Space Studies (GISS) in New York, which monitors global surface temperatures on an ongoing basis. Average temperatures around the globe in 2011 were 0.92 degrees Fahrenheit (0.51 degrees Celsius) warmer than the baseline in the mid-20th century.
"We know the planet is absorbing more energy than it is emitting," said GISS Director James Hansen. "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."
Essentially, low solar activity means less heat energy is reaching Earth, and if all other things were equal, that would mean cooler temperatures. However, a recent NASA report released this month revealed this prolonged lull in the sun's activity did not prevent the Earth from absorbing more solar energy than it let escape back into space. These results confirm greenhouse gases produced by human activities are the most important driver of global climate change, according to the researchers led by Hansen.
These greenhouse gases, particularly carbon dioxide, absorb infrared radiation emitted by Earth and release that energy into the atmosphere rather than allowing it to escape to space. Over time, as the gas concentrations have increased and, in turn, more energy gets trapped, the globe has seen higher temperatures.
This long-term GISS temperature record allows scientists to get a handle on global warming. Because of the large natural variability of climate, scientists don't expect temperatures to rise consistently year after year. However, they do expect a continuing temperature rise over decades. And that's what they are finding: The difference between 2011 and the warmest year in the GISS record, 2010, is 0.22 degrees F (0.12 degrees C).
In addition, the record shows the first 11 years of the 21st century experienced notably higher temperatures compared with the middle and late 20th century, Hansen said. The only year from the 20th century to make the list of top 10 warmest years on record is 1998.
The results come from weather data collected at more than 1,000 meteorological stations around the world, satellite observations of sea-surface temperature and Antarctic research station measurements.
Hansen said he expects record-breaking global average temperature in the next two to three years, because solar activity is on the upswing and the next El Niño will increase temperatures in the tropical Pacific Ocean.
"It's always dangerous to make predictions about El Niño, but it's safe to say we'll see one in the next three years," Hansen said. "It won't take a very strong El Niño to push temperatures above 2010."