You know it. But attend to this:
 The existence of a global current that influences weather worldwide was first proposed by oceanographer Wallace Broeker in the early 1990s.
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Taylor has expanded a theory that was first introduced in the early 1990s by oceanographer Wallace Broeker that suggests the presence of a global-scale current, operating on a time scale of several decades, which affects worldwide weather patterns. Broeker was looking for possible reasons for the last ice age when he discovered the conveyer belt. Meteorologist William Gray of Colorado State University also related the theory to his work in predicting Atlantic hurricanes.
"Since the theories were developed, we've identified several things that correlate most closely to high levels of conveyor belt activity," said Taylor. "Certainly one of the most prominent is Atlantic Ocean hurricanes. Also very clear is more La Niña years; and wetter, cooler conditions in the Pacific Northwest. In fact, we have a graph showing the tight correlation between severe hurricane seasons like the one we're now having, and wet winter conditions in Portland, Oregon."
The conveyor belt works by transporting warm ocean water from the Pacific Ocean through the Indian Ocean and into the Atlantic Ocean. In the north Atlantic, the warm water, which turns very salty due to evaporation during the journey, runs into cold water coming down from the north. The warm water cools quickly, and sinks due to greater density. This creates a sub-surface countercurrent which carries the cool water back to the Indian and Pacific oceans.
And cold water in the Pacific Ocean tends to produce the type of La Niña years that, among other things, makes Oregon even colder and wetter than usual in the winter, according to Taylor. More El Niño events take place when the conveyor belt is inactive.
"When the conveyor belt is in high gear, the Atlantic tends to be warmer than usual and the Pacific is cooler," Taylor said. "Then the cycle seems to die down for about 20 years."
Unusually warm water fuels more frequent and violent hurricanes and the correlation is particularly strong for Atlantic Ocean hurricanes, Taylor said. The quietest four years of the last 50 years were from 1991 to 1994, but then 1995 had the largest number of hurricanes since storms were first named in the early 1950s. The latest four-year period is the busiest on record.
"Temperatures in the Atlantic are about two to four degrees warmer than normal right now, while the Pacific Ocean is relatively cold," said Dr. Timothy Liu, SeaWinds project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Those conditions have forced the jet stream much farther north and created a corridor for newly born hurricanes to move unimpeded toward the Atlantic coast." The jet stream is a high-speed wind current that generally blows westerly at 10 to 15 miles above the Earth's surface.
 This graph shows weather patterns associated with the conveyor belt. (Note: PNW is Pacific Northwest.) |
"This hurricane season started late, but it's already had about an average amount of hurricane activity and it's only halfway over," Taylor said. "It's going to be a very busy hurricane season, just as four of the last five years have been. And the Pacific Northwest is going to have its sixth year in a row of wetter than average weather. This is not a coincidence. If you want to understand what is happening, you have to look at some of the climate forces that are driving it."
East Coast and Gulf Coast cities are in for at least 15 more years of unusually frequent and destructive hurricanes. And residents of traditionally soggy Oregon and Washington can expect wet, snowy winters with some regularity, said Taylor.
Over the last 100 years, four distinct periods-two when the conveyor belt was very active and two when it was quite inactive-were identified by Gray and a colleague. Global temperatures seem to correspond to the active-inactive phases and since the tropical Pacific is the largest terrestrial heat source to the atmosphere; when the Pacific warms, so does the atmosphere. This should not be surprising, according to Taylor. During El Niño events, the Pacific temperatures overall warm significantly.
All signs point to a switch in the conveyor belt to active, forecasting a mostly wet climate for the next 20 years or so. If history repeats itself, expect frequent floods, no droughts and about 75 percent of all years in the cycle to be wetter than average and relatively cool, according to Taylor. This active phase began in 1995 and will last for 20 to 25 years before calming down again. It's a pattern separate from and not to be confused with possible global warming caused by the greenhouse effect, warns Taylor.
"Following the very dry 1975-94 period, which saw two significant statewide droughts in Oregon and 10 consecutive dry years, we are now completing the fifth consecutive above average year for precipitation in the Pacific Northwest," said Taylor.
It's still not certain what causes the conveyor belt to kick into gear. One likely candidate is fluctuations in the sun's magnetic field, which affects the amount of solar energy reaching the Earth and tends to change on a 20- to 27-year cycle, said Taylor. What is far more certain, he said, is the implication of the trend once it's clearly under way.
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