Understanding Climate

In 2011, La Niña and the Pacific Decadal Oscillation cooled parts of the Pacific Ocean, but unusually warm temperatures predominated elsewhere.

In 2011, annual snow cover extent over Northern Hemisphere continents (including the Greenland ice sheet) averaged 24.7 million square kilometers, which is 0.3 million square kilometers less than the long-term average.

In early 2011, stratospheric temperatures rose over the tropics due to La Nina while temperatures over the poles fell below the long-term average.

Data from 2010 indicate that mountain glaciers predominantly lost mass, and preliminary data from 2011 indicate a continuation of the same long-term trend.

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.

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.

It is virtually certain our world will continue to warm over this century and beyond. The exact amount of warming that will occur in the coming century depends largely on the energy choices that we make now and in the next few decades.

The Arctic of recent years—warmer, greener, less icy—is likely to be the new normal for the Far North. One sign of the ongoing transformation of the Arctic is the spread of shrubs across the tundra.