Understanding Climate

Except for some La Niña-cooled regions of the tropical Pacific and a few other cool spots, the upper ocean held more heat than average in 2011 in the Pacific, Atlantic, Indian, and Southern Oceans.

In 2011, Earth’s atmosphere was cooler and drier than it had been the previous year, but it was more humid than the long-term average.

Despite the double-dip La Nina that occurred throughout the year, 2011 was still among the 15 warmest years on record. Including the 2011 temperature, the rate of warming since 1971 is now between 0.14° and 0.17° Celsius per decade (0.25°-0.31° Fahrenheit), and 0.71-0.77° Celsius per century (1.28°-1.39° F) since 1901.

In 2011, global sea levels fell below the long-term trend of sea level rise, but as La Niña waned late in the year, global ocean levels began rising rapidly.

In September 2011, Arctic sea ice reached its second-lowest minimum extent in the satellite record.

In the spring of 2011, scientists observed the largest, most severe ozone destruction ever witnessed in the Arctic since records began in 1978, due in part to the fact that CFCs stick around in the atmosphere for a very long time. Climate maps reveal the cause to be unusually persistent cold temperatures.

The lead character in the 2011 climate story was La Niña—the cool phase of the El Niño-Southern Oscillation—which chilled the central and eastern tropical Pacific at both the start and the end of the year. These natural cooling events have a long reach: many of the big climate events of 2011, including famine-inducing drought in East Africa, an above-average hurricane season in the Atlantic, and record rainfall in many parts of Australia, are common “side effects” of La Niña.

NOAA scientists have documented a new impact of the increasingly thin blanket of Arctic sea ice: gases escaping from the thinner ice in spring are affecting air chemistry, reducing ground-level ozone, and likely increasing mercury contamination.

Record and near-record breaking temperatures dominated the eastern two-thirds of the nation and contributed to the warmest March in the contiguous United States since records began in 1895. The average temperature was 8.6 degrees above the 20th century average for March. In the past 117 years, only one month (January 2006) has ever been so much warmer than its average temperature.

When NOAA’s National Climatic Data Center crunched the numbers for December, January and February—”meteorological” winter for 2011-2012—it stacked up as the fourth warmest of the past 117 winters. Virtually all of the West received less than its average precipitation.