July 27, 2009 -- Two years after the sun peaks in its 11-year cycle, Earth's climate undergoes small El Nino-like warming effects, which have been tied to floods, droughts and other weather systems.
So concludes a new study that is one of the first to link cyclical variations in solar activity to Earth's climate.
The research, led by scientists at the National Center for Atmospheric Research (NCAR) in Colorado, is based on computer models of ocean surface temperatures recorded between 1890 and 2006.
The team then simulated how changes in solar output -- which varies only by about 0.1 percent throughout the sun's 11-year cycle -- would impact temperatures on Earth.
They discovered that solar max slightly elevates atmospheric heating, particularly over the tropical and subtropical Pacific, where sun-blocking clouds are scarce.
The extra heat leads to more evaporation, which in turn increases the amount of water vapor in upper-atmospheric winds, triggering heavier rains in the western tropical Pacific and cooler, drier conditions in the east.
The researchers found an El Nino-like warming event occurs about two years after solar max and lasts about a year.
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"There's still a lot of uncertainty about how much total radiation from the sun influences Earth's climate," said NCAR senior scientist Warren Washington, who has been studying the climate for 45 years.
"This is one of the very first papers to make a connection."
Washington added that global warming impacts from solar cycle variations are small compared to overall global warming trends.
The computer models did take into account changes in greenhouse gases, though the main focus of the study was to distinguish how changes of the sun impacts climate.
The studies, however, did not analyze specific weather patterns generated by solar cycle variations. El Nino typically causes flooding, draught and other disturbances. A companion cooling phenomenon called La Nina triggers relatively warm and dry conditions across the western part of North America.
"Building on our understanding of the solar cycle, we may be able to connect its influences with weather probabilities in a way that can feed into longer-term predictions a decade at a time," wrote NCAR scientist Gerald Meehl, lead author of the paper which appeared in this month's Journal of Climate.
The sun is at the start of a new 11-year cycle that is forecast to peak in 2013.
Related Links:
Irene Klotz's Blog: Free Space
TreeHugger.com: Global Ocean Temperatures Warmest Since Records Began in 1880 (129 Years Ago!)
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