For comparison: Including energy for transport, manufacturing, heating and cooling, residential electricity, etc., it takes about 324 billion watts to power the United States. That is about 1/4000th of the 1.3 petawatts of power in the Atlantic Ocean’s northward heat transport.

Seasons: Winter, Spring, Summer, Fall

Sources: Energy Information Administration. Annual Energy Review, 2010. Accessed Online 28 January 2012 <http://www.eia.gov/totalenergy/data/annual/index.cfm> and Send, Uwe et al. “Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data.” Geophysical Research Letters 38 (2011): L24606.

Rains in East Africa primarily fall during the long rains (March through May) and the short rains (October through December). Understanding how climate and climate change influence these rains is particularly important for predicting drought in the region.  Conditions in the tropical Pacific affect weather throughout the world and the tendency for the tropical Pacific to persist in either cool La Niña phases or warm El Niño phases enable forecasters to predict whether seasonal temperatures or precipitation levels will be above or below average. In addition to local Indian Ocean sea surface temperatures, the short rains in East Africa are strongly influenced by conditions in the tropical Pacific, with La Niña phases leading to reduced precipitation. How the tropical Pacific affects the long rain season, on the other hand, is harder to identify. Recent work shows that since 1999, the long rains have been consistently weak and unable to compensate for reduced short rain precipitation during La Niña phases, leading to drought conditions like those experienced in 2011. Also since 1999, there has been a pattern of consistently elevated sea surface temperatures in the western tropical Pacific and consistently high rainfall levels in that region. The tendency of ocean surface temperatures to remain in particularly warm or cool conditions for relatively long periods of time, coupled with what is known about the atmospheric links between the western tropical Pacific and East Africa, enables forecasters to better understand and predict droughts there.

Seasons: Winter, Spring, Summer, Fall

Source: Lynn, B and DeWiltt, DG. “A recent and abrupt decline in the East African long rains.” Geophysical Research Letters 39 (2012): L02702. 

Earth’s ocean is mixed by a complex system of currents. Downwellings occur when currents move water from the surface to the depths and upwellings occur when nutrient-rich waters are pulled from the depths to the surface. Upwelling areas are some of the most productive waters in the world, including the California Coast where part of the California Current System upwells. The waters along the California Coast are more or less productive during some years, based on the strength and timing of this upwelling. Waters are less productive during years when the winter upwelling is delayed and weaker. This upwelling strength is indexed by the North Pacific Gyre Oscillation (NPGO) – in positive NPGO years, the upwelling starts about six weeks earlier than negative NPGO years. The NPGO is an expression of the variability in the pressure difference between a high pressure center located near Hawaii and a low pressure center in the Gulf of Alaska. This variability leads to changes in the strength and position of the winds that run along the California Coast and work to “pull” a current of water from the depths. Compared to negative NPGO years, average end of winter water conditions during positive NPGO years feature nitrate concentrations that are about 25 percent higher, chlorophyll concentrations about 15 percent higher and zooplankton numbers that are about 20 percent higher. These nutrients and zooplankton  feed commercially-important fish species and seabirds.

Seasons: Winter, Spring

Sources: Chenillat, F et al. “North Pacific Gyre Oscillation modulates seasonal timing and ecosystem functioning in the California Current upwelling system.” Geophysical Research Letters 39 (2012): L01606 and Di Lorenzo, E et al. “North Pacific Gyre Oscillation links ocean climate and ecosystem change.” Geophysical Research Letter 35 (2008): L08607.

AO: The Arctic Oscillation (AO) is the difference in atmospheric pressure between the Arctic and the mid-latitudes of the Northern Hemisphere. Upper-atmospheric westerly winds and mid-latitude winter storms are stronger during “positive phases” of the AO (when the pressure difference is greater), and these stronger winds serve as a “blocking” mechanism that keeps the frigid Arctic air in the Arctic instead of invading many midlatitude areas, particularly the Eastern United States, leading to milder winter temperatures there. Negative phases work the opposite way, with less blocking and a colder eastern United States.

So far, the Arctic Oscillation has favored mild winter temperatures in the Eastern United States (http://www.climatewatch.noaa.gov/image/2011/so-far-arctic-oscillation-favoring-mild-winter-for-eastern-u-s)

Useful Climate Analogy: The Arctic Oscillation and Your Refrigerator Door. 

http://www.earthgauge.net/2011/analogies-of-basic-physical-principles#arctic The El Niño-Southern Oscillation (ENSO) is a periodic shift in tropical Pacific sea surface temperature distributions. During cool La Niña phases, the northern hemisphere storm track tends to move farther north, leading to a wetter northern tier of the United States – particularly a wetter Northwest – and a drier southern tier. El Niño phases bring relatively the opposite conditions.

NOAA’s Winter Weather Outlook (http://www.climatewatch.noaa.gov/image/2011/2011-2012-winter-outlook) gives different regional probabilities for warmer/colder or wetter/drier conditions. Variation in this outlook is driven largely by differences in the state of the El Niño-Southern Oscillation.

Regional Outlooks:

Albany, Georgia Winter Outlook: The Albany area has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Albuquerque, New Mexico Winter Outlook: The Albuquerque area has equal chances of experiencing well above or well below normal winter temperatures and has a 33 to 40 percent chance of receiving below average precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Anchorage, Alaska Winter Outlook: The Anchorage region has equal chances of experiencing well above or well below normal winter temperatures and an equal chance of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Arizona Winter Outlook: Most of Arizona has equal chances of experiencing well above and well below normal winter temperatures and a 33 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Asheville, North Carolina Winter Outlook: The Asheville region has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Atlanta, Georgia Winter Outlook: The Atlanta area has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Bismarck Winter Outlook: The Bismarck area has a greater than 40 percent chance of experiencing well below normal winter temperatures and a 40 to 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

California Winter Outlook: Most of California has a greater than 40 percent chance of experiencing well below normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Carbondale, Illinois Winter Outlook: The Carbondale area has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Central Mississippi Winter Outlook: Central Mississippi has a greater than 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well below and well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Central North Carolina Winter Outlook: The Central North Carolina region has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Central Oklahoma Winter Outlook: Central Oklahoma has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Colorado Springs Winter Outlook: The Colorado Springs region has equal chances of experiencing well above and well below normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Dallas, Georgia Winter Outlook: The Dallas region has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well below and well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Dayton, Ohio Winter Outlook: The Dayton region has equal chances of experiencing well above and well below normal winter temperatures and a greater than 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Eastern Nebraska Winter Outlook: The Eastern Nebraska region has equal chances of experiencing well above and well below normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Eastern Tennessee Winter Outlook: Eastern Tennessee has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Fairbanks, Alaska Winter Outlook: The Fairbanks region has a greater than 40 percent chance of experiencing well below normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Fallon, Nevada Winter Outlook: The Fallon region has a 33 to 40 percent chance of experiencing well below normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Florida Panhandle Winter Outlook: The Florida Panhandle region has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Grand Forks, North Dakota Winter Outlook: The Grand Forks area has a greater than 40 percent chance of experiencing well below normal winter temperatures and a 40 to 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Iowa Winter Outlook: Most of Iowa has equal chances of experiencing well above or well below normal winter temperatures and equal chances of receiving well above or well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period. A predominately positive Arctic Oscillation has so far favored mild winter temperatures in the region.

Kansas Winter Outlook: Most of Kansas has a 33 to 40 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Little Rock, Arkansas Winter Outlook: The Little Rock region has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Louisiana Winter Outlook: Most of Louisiana has a greater than 50 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Lubbock Winter Outlook: The Lubbock area has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a greater than 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Memphis, Tennessee Winter Outlook: Memphis has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Minnesota Winter Outlook: Most of Minnesota has a 33 to 40 percent chance of experiencing well below normal winter temperatures and a 33 to 40 percent chance  of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Missoula, Montana Winter Outlook: The Missoula region has a 33 to 40 percent chance of experiencing well below normal winter temperatures and a greater than 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Missouri Winter Outlook: The State of Missouri region has a 33 to 40 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well below and well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Mobile, Alabama Winter Outlook: The Mobile area has a greater than 50 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Nashville, Tennessee Winter Outlook: The Nashville area has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Northeast Winter Outlook: The Northeast has equal chances of experiencing well above or well below normal winter temperatures and an equal chance of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period. A predominately positive Arctic Oscillation has so far favored mild winter temperatures in the region.

Northern Alabama Winter Outlook: Northern Alabama has a greater than 40 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well below or well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Northern California Winter Outlook: Northern California has a greater than 40 percent chance of experiencing well below normal winter temperatures and 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Northern Colorado Winter Outlook: The Northern Colorado region has equal chances of experiencing well above and well below normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Northern Florida Winter Outlook: The Northern Florida region has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a greater than 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Northern Mississippi Winter Outlook: Northern Mississippi has a 40 to 50 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well below and well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Ohio Winter Outlook: Most of Ohio has equal chances of experiencing well above and well below normal winter temperatures and a greater than 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Ohio Valley Winter Outlook: The Ohio Valley region has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a greater than 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Plentywood Winter Outlook: The Plentywood region has a greater than 40 percent chance of experiencing well below normal winter temperatures and a greater than 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Pocatello-Idaho Falls Winter Outlook: The Pocatello-Idaho Falls region has equal chances of experiencing well above and well below normal winter temperatures and around a 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Portland, Oregon Winter Outlook: The Portland region has a greater than 40 percent chance of experiencing well below normal winter temperatures and around a 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Rapid City, South Dakota Winter Outlook: The Rapid City region has equal chances of experiencing well above and well below normal winter temperatures and a 40 to 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Reno, Nevada Winter Outlook: The Reno area has a greater than 40 percent chance of experiencing well below normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Salt Lake City Winter Outlook: The Salt Lake City region has equal chances of experiencing well above and well below normal winter temperatures and around a 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

San Diego, California Winter Outlook: The San Diego region has a 33 to 40 percent chance of experiencing well below normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Sandpoint Winter Outlook: The Sandpoint region has a greater than 40 percent chance of experiencing well below normal winter temperatures and a greater than 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Santa Fe Winter Outlook: The Santa Fe region has equal chances of experiencing well above or well below normal winter temperatures and has a 33 to 40 percent chance of receiving below average precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Savannah, Georgia Winter Outlook: The Savannah area has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Socorro, New Mexico Winter Outlook: The Socorro region has equal chances of experiencing well above or well below normal winter temperatures and has a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

South Carolina Winter Outlook: Most of South Carolina has a 33 to 40 percent chance of experiencing well above normal winter temperatures and a 40 to 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

South Florida Winter Outlook: The South Florida region has equal chances of experiencing well above and well below normal winter temperatures and a greater than 60 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Spartanburg, South Carolina Winter Outlook: The Spartanburg region has a 40 to 50 percent chance of experiencing well above normal winter temperatures and a 33 to 40 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Springfield-Eugene, Oregon Winter Outlook: Most of Oregon has a greater than 40 percent chance of experiencing well below normal winter temperatures and a 40 to 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Texas Winter Outlook: Most of Texas has a greater than 50 percent chance of experiencing well above normal winter temperatures and a greater than 50 percent chance of receiving well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Twin Falls, Idaho Winter Outlook: The Twin Falls region has a 33 to 40 percent chance of experiencing well below normal winter temperatures and a 40 to 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Upper Midwest Winter Outlook: The Upper Midwest has equal chances of experiencing well above and well below normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Virginia Winter Outlook: Most of Virginia has a 33 to 40 percent chance of experiencing well above normal winter temperatures and equal chances of receiving well above and well below normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

Washington State Winter Outlook: Most of Washington State has a greater than 40 percent chance of experiencing well below normal winter temperatures and a greater than 50 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period.

West Virginia, Western New York and Western Pennsylvania Winter Outlook: The Western Pennsylvania and Western New York region has equal chances of experiencing well above or well below normal winter temperatures and a 33 to 40 percent chance of receiving well above normal precipitation levels. “Well above” and “well below” normal are defined by NOAA as conditions falling into the top or bottom third of climate conditions observed during the 1980 to 2010 period. A predominately positive Arctic Oscillation has so far favored mild winter temperatures in the region.

Volcanic eruptions can cool the Earth by injecting sulfur up into the stratosphere, the second layer of the atmosphere between five and 30 miles in altitude. The volcanoes increase stratospheric levels of tiny droplets of sulfuric acid, which work to reflect incoming sunlight. Volcanoes in the tropics, such as Pinatubo in the Philippines, which erupted in 1991 and Tambora in Indonesia, which erupted in 1815, are particularly good at cooling the planet because their emissions travel into both hemispheres. Even smaller volcanic eruptions, such as the 2006 Soufriére Hills (located in the Caribbean) and Tavurvur (Papua New Guinea, South Pacific) eruptions, are clearly noticeable to scientists taking measurements of the aerosol content of the stratosphere. These measurements show significant variability in stratospheric aerosol content. Overall aerosol loads increased by between five and nine percent each year from the 1960s through the 1980s, and then declined during the 1990s. They have been rebounding since 2000. The causes behind these trends are not entirely understood, although rises and declines in aerosol levels following volcanic eruptions are evident and relatively predictable. The Earth’s warming trend experienced since the 1960s would likely have been more pronounced without the accompanying trend of increased stratospheric aerosol content.

Seasons: Winter, Spring, Summer, Fall

Source: Solomon, S et al. “The Persistently Variable ‘Background’ Stratospheric Aerosol Layer and Global Climate Change.” Science 333 (2011): 866-869.

Every place in the world has its own climate with its own average temperature and precipitation levels. Some places around the world, such as most equatorial rainforests, experience little seasonal variation and are hot and wet throughout the year. Locations closer to the poles have more seasonal climates. The Northeast United States, for example, has rainfall evenly spread throughout the year, but the summer months are much warmer than the winter months. In some locations in the tropics, temperatures don’t change much throughout the year, but there are defined wet and dry seasons. Similarly, from year to year some places have little rainfall variance while other locations can be considerably wetter or drier. Such inter-annual variability in rainfall can be particularly pronounced in parts of Amazon. Inter-annual rainfall variability in the Amazon is driven by surface temperature shifts every few years in the waters of the equatorial Pacific Ocean, and shifts on longer time scales in the tropical and subtropical Atlantic Ocean. These water temperature shifts move winds, affecting rainfall patterns on land. If it was not for the plants of the Amazon, however, this variability would be even greater. Wetter years, or years with wetter wet seasons and/or shorter dry seasons, are years when vegetation flourishes. More vegetation means more evapotranspiration, the movement of moisture from the soil through plants to the atmosphere. More evapotranspiration means more rainfall. This increase in rainfall helps to keep the wet conditions going into the next year, even if other factors would favor drier conditions. Drier years tend to stress vegetation, leading to less evapotranspiration and less rainfall, which perpetuates these dry conditions into the following year. This means that years following severe droughts, such as the “once-in-a-century” 2010 Amazon drought, may be more susceptible to further droughts. It also means that there is more year-to-year continuity of rainfall levels than there would otherwise be.

Seasons: Winter, Spring, Summer, Fall

Source: Wang, G et al. “Vegetation dynamics contributes to the multi-decadal variability of precipitation in the Amazon region.” Geophysical Research Letters 38 (2011): L19703.

The 2007 September Arctic sea ice minimum extent was the smallest on record. This ice has been in a declining trend since 2002, with warmer temperatures favoring melt and prevailing winds favoring ice transport out of the Fram Strait between Greenland and Scandinavia. There has been a slight recovery in ice levels since 2008, although the multiyear ice extent in March 2011 was lower than it was in any year prior to spring 2008, following the fall 2007 record minimum. The measurement of multiyear ice, or ice that has survived at least one melt season, is important for assessing the robustness of the Arctic sea ice, which has traditionally been a permanent, not seasonal, feature of the North Pole. Between 1980 and 2011, the percent of multiyear sea ice present in March declined by 33 percent, while the percentage of multiyear ice at the September minimum declined by 50 percent. In March 2011, only about 45 percent of the ice present in the Arctic was multiyear ice, compared with 75 percent in 1980. Additionally, in March 1980, about 50 percent of the ice cover was particularly old ice (older than five years), whereas by this March that number had declined to 10 percent. The last four years have seen a marked decline in the survival rate of multiyear ice, which is now at 74 percent, compared to the 1980 to 2006 period when the survival rate was 90 percent.

Seasons: Summer

Source: Maslanik, J et al. “Distribution and trends in Arctic sea ice age through spring 2011.” Geophysical Research Letters 38 (2011): L13502.

The eruption of Iceland’s Laki volcano from June 8, 1783 to February 1784 had widespread and devastating consequences the world over. The event was one of the biggest natural disasters in British history, with sulfuric acid gas fumes killing over 23,000 Britons. The gas plume initially caused heat waves in Europe before spreading around the globe and cooling the rest of the Northern Hemisphere. Both France and Japan experienced crop failures and famines that year, and Alaskan tree ring records tell of a remarkably cold summer in North America. The Inuit remember it as “the summer that did not come.” The following winter was remarkably cold as well, with Europe being around 3.6 degrees Fahrenheit below normal and eastern North America having temperatures 8.6 degrees Fahrenheit below the 225 year mean. Early Americans skated on the harbor ice of Charleston, South Carolina, the Mississippi River was frozen at its delta, ice floes floated through the Gulf of Mexico and the Chesapeake Bay had its longest freeze-over on record. But was this severely cold winter caused by Laki’s eruption? According to tree ring proxy records used to reconstruct conditions in the tropical Pacific Ocean and North Atlantic over the centuries before instrumental data, at least part of the winter’s severity was due to a strong El Niño in the tropical Pacific and a strongly negative North Atlantic Oscillation (NAO). The strong El Niño event shifted storm tracks to the south, bringing frequent winter storms to the southern United States, while the strongly negative NAO allowed frigid Arctic air masses to easily sweep southward into the mid-latitudes. The coincidence of these conditions, as a result of serendipitous sea surface temperature variability, is similar to what happened during the 2009-2010 winter, which brought record cold to parts of the United States.

Seasons: Winter, Spring, Summer, Fall

Source: D’Arrigo R, et al. “The anomalous winter of 1783-1784: Was the Lake eruption or an analog of the 2009-2010 winter to blame?” Geophysical Research Letters 38 (2011): L05706.

Estimating how Earth’s climate varied before the modern period of instrumental records requires looking at natural records. How much a tree grows each year depends on how optimal the conditions are (i.e. whether they get sufficient water and sunlight, have a longer frost-free season, etc.). Analyzing differences in tree ring width is therefore a reasonable way to study past climate variability. Another annual recorder of weather variability is ice sheet accumulation. Each year, the Antarctic and Greenland ice sheets accumulate layers of snowfall, which is compacted and covered by the following year’s snowfall. Annual variability in ice accumulation follows temperature and precipitation variability, which is in turn determined by sea-surface temperatures and large scale circulation patterns, such as the North Atlantic Oscillation (NAO). The NAO is a measure of the difference in atmospheric pressure between the Arctic and the subtropical Atlantic – this pattern has a strong influence over winter weather in the midlatitudes.

More than 80 ice cores have been taken from locations on the Greenland Ice Sheet where ground-based radar, aircraft and satellite altimetry measurements have also been made. These modern measurements, along with current temperature and precipitation data, enable researchers to establish relationships between weather variables and annual ice accumulation. Understanding this relationship, as well as having a written record of Icelandic volcanic eruptions that correspond to the volcanic ash that is recorded in the ice cores, gives us a record of annual weather variability in Greenland. One ice core with visible annual layers revealed atmospheric conditions back to the year 1673, based on an average accumulation of 14 inches of ice each year.

Learn more about how paleoclimatologists study past climate variability in the upcoming Climate Fact Sheet, Coring for Clues: Reconstructing Climates of the Past.

Seasons: Winter, Spring, Summer, Fall

Sources: Mosley-Thompson, E et al. “Regional sensitivity of Greenland precipitation to NAO variability.” Geophysical Research Letters 32 (2005): L24707 and Banta JR and McConnell, JR. “Annual accumulation over recent centuries at four sites in central Greenland.” Journal of Geophysical Research: Atmospheres 112 (2007): D10114 and Bales, RC et al. “Annual accumulation for Greenland updates using ice core data developed during 2000-2006 and analysis of daily coastal meteorological data.” Journal of Geophysical Research: Atmospheres 114 (2009): D06116.

Trivia Question: What is the best way to predict what kind of winter you will have?

a) Look at how intense the Sun is right now
b) Look at how much ice there is in the Arctic
c) Look at sea surface temperatures in the tropical Pacific Ocean
d) Watch squirrel behavior

The correct answer is c. If you want to know what sort of winter you will have, you need to know what the prevailing winds are likely to be. In the tropical Pacific, huge masses of warm and cold water move around on cycles of 3-7 years. When warm waters cover the Pacific, an El Niño is happening. When the eastern Pacific is relatively cold, a La Niña is happening. These warm and cold water masses are large enough to influence how the atmosphere circulates, particularly the strength and position of the jet streams that drive the strength and position of mid-latitude winds. What these winds do determines what kind of winter we have in different parts of the United States.

Above: A schematic diagram of how El Niño and La Niña affect the jet streams and America’s weather.  Image Courtesy of NOAA Climate Prediction Center/NCEP/NWS

Season: Winter

Source: NOAA: Climate Prediction Center. “Frequently Asked Questions About El Niño and La Niña” Accessed Online 6 December 2010

Climate Center: La Nina Update from Climate Central on Vimeo.

For a broadcast-quality animation of 2010 month by month ice shrinking, as well as a visual showing what an equivalent 22 percent loss of the contiguous United States would look like, visit NOAA’s Environmental Visualization Laboratory.

Another measure of the state of the Arctic sea ice is the ratio of the multi-year ice (“old” ice that has survived at least one melt season) to the amount of purely seasonal ice. “Old” ice is thicker than the seasonal ice and requires more energy to melt. Between 2004 and 2008, the ice thinned by a basin-wide average of 2.2 feet. In 2003, 62 percent of the total volume of Arctic ice was “old” ice and 38 percent was seasonal ice. Between 2004 and 2008, the area covered by “old” ice shrank by 595,000 square miles. The percentages of “old” ice and seasonal ice are now 32 and 68, respectively. These numbers will be updated once the 2010 data is analyzed.

Image Above: A comparison of the differences between the September 10, 2010 sea ice minimum and the record low September 16, 2007 minimum. The light gray shading indicates areas where ice existed in both 2007 and 2010, the white areas are where ice existed in 2010 but not 2007, and the dark gray areas where ice was in 2007 but not 2010.

Season: Fall

Sources: Kwok, R et al. “Thinning and volume loss of the Arctic Ocean sea ice cover: 2003-2008.” Journal of Geophysical Research, Oceans 114 (2009): C07005, doi:10.1029/2009JC005312 and National Snow and Ice Data Center. “Arctic sea ice reaches annual minimum extent.” 15 September 2010. Accessed online 17 September 2010 < http://nsidc.org/arcticseaicenews/> and National Oceanic and Atmospheric Administration. “Arctic Sea Ice Reaches the 3rd Lowest Extent on Record.” Accessed Online 17 September 2010 http://www.nnvl.noaa.gov/MediaDetail.php?MediaID=521&MediaTypeID=2.

Trivia Question: All other things being equal, during what phase of ENSO does the Atlantic Hurricane season tend to be most active?

a. El Niño
b. La Niña
c. Neutral

The correct answer is b. The amount of vertical wind shear over the ocean can make or break a hurricane season. Vertical wind shear is the change in the speed and direction of wind at different levels of the atmosphere. More vertical wind shear, or lots of variation in wind speed across different altitudes, suppresses hurricane activity. Less vertical wind shear, or more even wind patterns across different altitudes, promote hurricane development. La Niña phases work to reduce the amount of vertical wind shear over the North Atlantic, and thus La Niña years tend to be years with more active Atlantic hurricane seasons. La Niña conditions are now present in the tropical Pacific.

Seasons: Summer, Fall

Sources: Briggs, WM. “On the Changes in the Number and Intensity of North Atlantic Tropical Cyclones.” Journal of Climate 21 (2008): 1387-1402. Donnely, JP and Woodruff, JD. “Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon.” Nature 447 (2007): 465-468.

Trivia Question: During warm periods in the Arctic, is the Antarctic generally:

a)    Also warmer than normal
b)    In an opposite cool phase
c)    Antarctic temperatures were steady over the 20th century
d)    No positive or negative relationship between Arctic and Antarctic temperatures exist

The correct answer is b. Periods when the Arctic is warmer than normal tend to be periods when Antarctica is cooler than normal and vice-versa. This “bipolar seesaw” phenomenon has been linked to well-documented shifts in ocean circulation, specifically the 65-70 year Atlantic Multidecadal Oscillation. Strong winds around Antarctica bring salty waters from the ocean depths to the surface. These waters are heated by the sun and Atlantic surface currents take the warm and salty waters North. When this process is at its most efficient, more warm water is transported to the far north, warming the Arctic and cooling the Antarctic. When the process is not efficient, more warm water stays around Antarctica, warming that continent instead of the Arctic. This general pattern has been observed in long-term (millennial) paleo-ice core records. The last 30 years have been different, however, with a dramatically warmer Arctic without a corresponding cooling of the Antarctic.

Seasons: Winter, Spring, Summer, Fall

Source: Chylek, P et al. “Twentieth century bipolar seesaw of the Arctic and Antarctic surface air temperatures.” Geophysical Research Letters 37 (2010): L08703.

Trivia Question: Have such prolonged dry episodes become more or less common over the past 60 years?

a)    More common
b)    Less common
c)    No change

The correct answer is b. Despite drought conditions in the late 1990′s and early 21st century, there appears to be an overall trend of fewer prolonged dry events in the Southwest since the 1950′s. This is especially true for the cold season (October through March), due to the more El Niño events in the eastern tropical Pacific Ocean over the study period. El Niño events work to steer the Northern Hemisphere storm track right over the desert Southwest. Also, since the mid-1970′s, the North Pacific Ocean has been in a “warm” phase of the Pacific Decadal Oscillation. Warm phases help to enhance the effects of El Niño events on Southwest rainfall. An overall warming, however, and thus an increase in soil evaporation, may be counteracting the effect this increase in precipitation has on streamflow levels.

Seasons: Winter, Spring, Summer, Fall

Source: McCabe, GJ et al. “Variability and trends in dry day frequency and dry event length in the southwestern United States.” Journal of Geophysical Research: Atmospheres 115 (2010): D07108.

Trivia Question: Which is another well-documented climate teleconnection?

a. Flooding in India resulting in sea-level rise around Manhattan
b. Mudslides in California causing snow in Maryland
c. Warm North Atlantic sea-surface temperatures leading to more wildfires in the western U.S.
d. Thunderstorms in Omaha leading to drought in Kazakhstan

The correct answer is c. While there may be some spurious correlation between some of the other events listed, analysis of over 500 years of proxy data from the West illustrates that wildfires there are more frequent when sea-surface temperatures in the North Atlantic are warm. Temperatures in the North Atlantic fluctuate between warm and cool conditions on a period of about 65 years, a phenomenon known as the Atlantic Multidecadal Oscillation.

Seasons: Winter, Spring, Summer, Fall

Source: Maue, Ryan N. “Northern Hemisphere Tropical Cyclone Activity.” Geophysical Research Letters 35 (2009): L05805 and Kitzberger, T et al. “Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America.” Proceedings of the National Academy of Sciences 104 (2007): 543-548 and eGaetana, AT et al. “Statistical Prediction of Seasonal East Coast Winter Storm Frequency.” Journal of Climate 15 (2002): 1101-1117 and Hirsch, ME et al. “An East Coast Winter Storm Climatology.” Journal of Climate 14 (2001): 882-899 and Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093 and National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif

Trivia Question: What phase has been more common over the last 25 years?

a) El Niño
b) La Niña

The correct answer is a. El Niño events have become more common since the mid-1970′s. Duing the 1950′s and 1960′s, La Niña events were more common.  See below for a graph of the last 60 years of El Niño (red) and La Niña (blue) event frequency.

Seasons: Winter, Spring, Summer, Fall

Sources: Kim, HM et al. “Impact of Shifting Patterns of Pacific Ocean Warming on North Atlantic Tropical Cyclones.” Science 325 (2009): 77-80 and Twine, TE et al. “Effects of El Niño-Southern Oscillation on the Climate, Water Balance, and Streamflow of the Mississippi River Basin.” Journal of Climate 18 (2005): 4840-4861 and Meehl, GA et al. “Current and Future U.S. Weather Extremes and El Niño.” Geophysical Research Letter 34 (2007) L20704 and Easterling, David. “Observed Climate Variability and Change.” NOAA/National Climatic Data Center. Ashville, NC: 31 January 2007 http://www.ametsoc.org/atmospolicy/documents/Easterling-Observed-Change-Jan-07.pdf and Meehl, GA et al. “Current and Future U.S. Weather Extremes and El Niño.” Geophysical Research Letter 34 (2007) L20704 and Easterling, David. “Observed Climate Variability and Change.” NOAA/National Climatic Data Center. Ashville, NC: 31 January 2007 http://www.ametsoc.org/atmospolicy/documents/Easterling-Observed-Change-Jan-07.pdf.

Trivia Question: During El Niño years such as this year, when the eastern tropical Pacific is relatively warm, does the Great Basin region have on average:

a. fewer frost days?
b. more frost days?

The correct answer is a. All other things being equal, the Great Basin region experiences fewer frost days during El Niño years compared to La Niña years.

Seasons: Late Winter, Early Spring, Fall

(Sources: Meehl, GA et al. “Current and Future U.S. Weather Extremes and El Niño.” Geophysical Research Letter 34 (2007) L20704 and Easterling, David. “Observed Climate Variability and Change.” NOAA/National Climatic Data Center. Ashville, NC: 31 January 2007 http://www.ametsoc.org/atmospolicy/documents/Easterling-Observed-Change-Jan-07.pdf)

Trivia Question: During El Niño years such as this year, when the eastern tropical Pacific is relatively warm, does the Pacific Northwest have on average:

a. fewer frost days?
b. more frost days?

The correct answer is a. All other things being equal, the Pacific Northwest experiences fewer frost days during El Niño years compared to La Niñ years.

Seasons: Late Winter, Early Spring, Fall

Sources: Meehl, GA et al. “Current and Future U.S. Weather Extremes and El Niño.” Geophysical Research Letter 34 (2007) L20704 and Easterling, David. “Observed Climate Variability and Change.” NOAA/National Climatic Data Center. Ashville, NC: 31 January 2007 http://www.ametsoc.org/atmospolicy/documents/Easterling-Observed-Change-Jan-07.pdf.

Trivia Question: During El Niño years such as this year, when the eastern tropical Pacific is relatively warm, does the Pacific Northwest have on average:

a. fewer frost days?
b. more frost days?

The correct answer is a. All other things being equal, the Pacific Northwest experiences fewer frost days during El Niño years compared to La Niña years.

Seasons: Late Winter, Early Spring, Fall

Sources: Meehl, GA et al. “Current and Future U.S. Weather Extremes and El Niño.” Geophysical Research Letter 34 (2007) L20704 and Easterling, David. “Observed Climate Variability and Change.” NOAA/National Climatic Data Center. Ashville, NC: 31 January 2007 http://www.ametsoc.org/atmospolicy/documents/Easterling-Observed-Change-Jan-07.pdf.