Changing water temperatures in the tropical Pacific Ocean may be signaling the start of a new El Nino, an event that could have worldwide impact, government scientists said. One recent El Nino was blamed for drought, typhoons and 1,500 deaths.
"The current situation deserves very close attention," the federal Climate Analysis Center said in a statement Friday.
The El Nino is characterized by unusually warm water conditions in the eastern tropical Pacific Ocean and by changes in air pressure over different parts of that ocean.
During previous El Ninos, water temperatures near the international date line have risen one to two degrees. While that may seem a small change, the slow rate at which water changes and the great amount of energy needed to warm such a large mass of water can make it a significant increase.
Years ago, when such changes tended to be first noticed by South American fishermen around Christmas, the phenomenon was given the name El Nino, which is Spanish for child, a reference to the baby Jesus.
The latest El Nino in 1986 was relatively mild, but one in 1982-83 led to weather changes that were blamed for 1,500 deaths and billions of dollars in damage across the globe.
"We don't want to say something is developing that could be like that, because that was exceptional," Dr. Vernon Kousky of the climate center said in a telephone interview.
The 1982-83 El Nino was blamed for worsening the devastating drought in Africa, causing a series of severe winter storms to come ashore in California, spawning the first typhoon to strike French Polynesia in 75 years _ followed by five more in five months _ deluging Peru and Ecuador with torrential rains and promoting the worst drought in two centuries in Australia.
Overall damage was estimated at $2-billion to $8-billion by a United Nations analysis.
Scientists suggest that was a once-in-a-lifetime event, though. The El Nino in 1986-87 was closer to average, with some weather changes reported but not the massive damage of the one before.
Kousky's office monitors sea surface conditions continually, and has learned the warning signs that an El Nino may be developing.
Current conditions are similar to those prior to the 1986 event, Kousky said. But, he added, "I can't really say how firm it looks. .
. There is nothing to say this will hang in there tough and continue on. We're just monitoring it carefully."
If it does build into a full-fledged El Nino, the impact could be felt worldwide.
The problem involves the relocation of warm water from one side of the Pacific Ocean to the other.
Normal conditions include strong easterly winds, which move the warm surface waters of the ocean toward Asia and allow cooler waters to rise up from the depths along the coast of South America.
But when an El Nino occurs, the easterly winds diminish or are replaced by westerlies, and the warm water sloshes back toward the Americas.
The fact that warm water is more likely to evaporate than cooler water means it has more warm air above it. Warm air is buoyant, tending to rise and cause its moisture to condense into clouds. That results in more rainfall in the warm area, Kousky said.
This rising air makes it easier to track the changes on satellite images, but it is also what leads to weather problems.
Having the warm water move eastward puts "precipitation and cloudiness in the central Pacific, where it normally isn't," said Kousky.
"The heating there strengthens the jet stream and upsets the normal wave pattern in the stream," he said. This affects the jet streams in both the North and South hemispheres, largely in winter in each half of the globe.
It's the movement of the jet stream, a high altitude river of fast-moving air going west to east, that guides weather across the world and often forms the boundary between cold polar air and warmer air to the south.
North-south loops in that stream usually move gradually around the Earth, but if something like an El Nino disrupts that progression, weather can be affected almost anywhere.
While scientists now track events that seem to lead to the El Nino, in past years it was generally first noticed by South American fishermen because the changes in water temperature tended to reduce the catch off their coasts. Indeed, a severe El Nino could virtually wipe out the catch for many species of fish.
El Ninos have been recorded periodically for many years, including 1975-75, 1972-73, 1969, 1965, 1963 and 1957. Evidence of the effects of El Ninos can be traced, in fact, back to 1532 when an unusually wet season apparently helped Pizarro and his Conquistadores cross normally desert areas in what is now Peru.