New El Niño stronger and more frequent than original
Friday, August 27, 2010, 16:40 (GMT + 9)
A relatively novel type of El Niño is becoming more frequent and increasingly powerful, according to a new study by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA). This new kind of storm has its warmest waters in the central-equatorial Pacific Ocean instead of the eastern-equatorial Pacific.
Lead study author, Tong Lee, of NASA's Pasadena-based Jet Propulsion Laboratory and Michael McPhaden, of NOAA's Seattle-based Pacific Marine Environmental Laboratory measured shifts in El Niño intensity since 1982. They analysed NOAA satellite data of sea surface temperature versus directly-measured ocean temperature data.
The strength of each El Niño was determined by how much its sea surface temperatures differed from the average. They determined that the intensity of El Niños in the central Pacific has almost doubled, with the most forceful taking place in 2009-10.
Stronger El Niños, the scientists said, help explain a fixed rise in central Pacific sea surface temperatures gauged over the past few decades, which some have blamed on global warming. But no noteworthy temperature increases were seen in years with neutral ocean conditions or when the storm’s cool water counterpart, La Niña, was present.
"These results suggest climate change may already be affecting El Niño by shifting the center of action from the eastern to the central Pacific," declared McPhaden. "If the trend we observe continues, it could throw a monkey wrench into long-range weather forecasting, which is largely based on our understanding of El Niños from the latter half of the 20th century."
El Niño is the oceanic factor of a climate pattern called the El Niño-Southern Oscillation that shows up in the tropical Pacific Ocean about every three to five years. El Niños can affect global weather patterns as well as the incidence and regularity of hurricanes, droughts and floods and even raise or lower temperatures by as much as 0.2 degrees Celsius across the globe.
Normally, during El Niño, the usually strong easterly trade winds in the tropical eastern Pacific Ocean wane, which thwarts the normal upward movement of cold subsurface waters and lets warm surface water from the central Pacific travel in the direction of the American continent. Abnormally warm surface water can then take up much of the tropical Pacific, leaving the maximum ocean warming in the eastern-equatorial Pacific.
But since the early 1990s, scientists have observed a new type of El Niño occurring ever more frequently. The maximum ocean warming is then found in the central-equatorial, instead of the eastern Pacific. A recent study concluded that several climate models predict that these phenomenons will occur much more commonly under projected global warming scenarios.
"It is important to know if the increasing intensity and frequency of these central Pacific El Niños are due to natural variations in climate or to climate change caused by human-produced greenhouse gas emissions," he said.
The study’s results were recently published in Geophysical Research Letters.
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By Natalia Real