29 July 2009
El Niño Climate Event Begins to Influence Global Weather, Oceans
Periodic warming of tropical Pacific waters expected to persist into 2010
This is the first in a series of articles about the El Niño climate phenomenon and its effects on global weather and ocean conditions.
Washington ― For the first time since 2006, a warming of ocean temperatures in the equatorial Pacific Ocean has alerted scientists to the arrival of El Niño, a recurring climate event that influences global weather, sea conditions and marine fisheries.
On July 9, National Oceanic and Atmospheric Administration (NOAA) scientists announced the arrival of El Niño and said they expected the event to continue developing during the next several months, with further strengthening possible. They expect the El Niño to last through the 2009–2010 winter season.
The announcement was based on observations by scientists from NOAA’s National Weather Service Climate Prediction Center that weekly eastern equatorial Pacific sea surface temperatures were at least 1 degree Celsius above average at the end of June.
“We’ve seen temperatures becoming increasingly warm over the last few months in the eastern half of the equatorial Pacific Ocean,” meteorologist Gerry Bell, NOAA’s lead seasonal hurricane forecaster, told America.gov. “During June the ocean temperatures were about 1 to 2 degrees Fahrenheit [1/2 to 1 degree Celsius] above average. Those warm temperatures meet the threshold for what we define as El Niño.”
OCEAN AND ATMOSPHERE
El Niño ― Spanish for “the boy child,” named in the late 1800s by Peruvian sailors who first noticed that a warm current sometimes appeared in local waters at Christmastime ― is the warmer-than-normal phase of an irregular cycle called the El Niño Southern Oscillation (ENSO). A cooler-than-normal phase that follows El Niño is called La Niña, the girl child.
El Niño events probably have been happening for millennia, but the El Niño that occurred in 1567–1568 was the first for which historical evidence is available. More recently, strong El Niño events were documented in 1972–1973, 1982–1983 and 1997–1998.
For the current El Niño, Bell said, “some of the computer models are indicating a moderate strength and some are indicating a strong event. There’s quite a bit of uncertainty right now. It’s just too far in advance.”
ENSO, Bell said, involves both the ocean and the atmosphere.
“When we talk about El Niño, we’re not just looking at ocean temperatures,” he said. “We’re also talking about weaker trade winds across the tropical Pacific Ocean and tremendous changes in rainfall across the tropics.”
For nations around the globe, the approach of this fledgling El Niño is good or bad, depending on the strength of the latest event and its effects on regional temperatures and precipitation.
EL NIÑO EFFECTS
ENSO events, especially the strongest ones, have been linked with impacts on almost every aspect of human life ― disease outbreaks, lower and higher agricultural yields, floods and drought, changes in energy demand, disrupted hydropower generation, fishery catch fluctuations, animal movements, forest fires and the economic well-being of vulnerable nations.
El Niño affects weather patterns worldwide. In the United States, it shifts the winter storm track and jet stream south of normal, so storms that usually come into the country through Pacific Northwest states Oregon and Washington instead come in through California and move across the country’s southern tier to Florida.
“The southern part of the country tends to be stormier and wetter during an El Niño winter and the northern part of the country tends to have a milder-than-normal winter,” Bell said.
The event brings much-needed rainfall to the normally dry southwestern United States, so not all El Niño effects are harmful. And El Niño tends to increase rapidly changing wind currents called wind shear, making winds less favorable to hurricane formation in the Atlantic Ocean.
El Niño’s biggest impacts are in the tropics, where the climate event arises. That includes most of Africa, southern India, southern Asia, Indonesia, New Guinea, northern Australia, southern Mexico, Central America and northern South America.
BAD TIMES
At the NOAA-funded International Research Institute (IRI) for Climate and Society, part of the Earth Institute at Columbia University in New York, climate scientists on July 17 forecasted an 80 percent probability that an El Niño would happen this year.
Tony Barnston, head of real-time forecasting at IRI, said countries in eastern equatorial Africa including Kenya and Uganda get more rainfall than average with an El Niño.
“But most places, in Africa and elsewhere, tend to get less rainfall when there’s an El Niño, and that’s more threatening to their livelihoods,” he said. “[Problems with] water management, drinking water, irrigation water, food security and drought just spell bad times for most people.”
Indonesia sees below-normal rainfall during an El Niño, as do northeastern Australia and southern Africa. In the eastern part of the Pacific, warmer waters can hinder a process called upwelling ― the rise of deeper, colder water to shallower depths, bringing nutrients to large populations of fish. During El Niño, fish swim into deeper waters to feed and fisheries suffer.
More information is available at the NOAA El Nino page and the IRI ENSO information site.
