Periodic peaks in the number of visible sunspots may help predict heavy rains and subsequent disease outbreaks in East Africa, according to a controversial new study. Although previously questioned, the sunspot-rainfall link suggests that many of East Africa’s wettest rainy seasons during the 20th century were closely associated with highpoints in the mysterious solar cycle that yields the sun’s large dark blotches.
The take-home message, researchers concluded in the latest issue of the Journal of Geophysical Research, is that careful scrutiny of past climatic conditions may generate better long-term predictions of destructive weather events in the future. That knowledge, in turn, may provide a crucial head start to those working to limit fallout such as erosion, flooding and mosquito-borne diseases like malaria and Rift Valley Fever.
J. Curt Stager, the report’s lead author and a paleoclimatologist at Paul Smith’s College in Paul Smiths, N.Y., said reaction to his research has been decidedly mixed, due in part to the checkered past of sunspot predictions.
“I’m afraid it suffers from the same failings as most of the purported surface climate-solar cycle connections,” said Gavin Schmidt, a climate modeler at NASA’s Goddard Institute for Space Studies in New York City. In an e-mail, Schmidt said that even uncorrelated “noise” in records with decadal variability, such as rainfall measurements, can sometimes yield apparent patterns if someone looks hard enough. But it doesn’t make those correlations significant.
“People have been looking for solar cycle effects in climate for 200 years,” Schmidt said. “If they were there, they’d have been found already.”
David Verardo, director of the National Science Foundation’s Paleoclimate Program, nevertheless praised the new results in a statement as “an important step in applying paleoclimate analyses to predicting future environmental conditions and their impacts on society.” The foundation provided major funding for the study.
Sunspots, or slightly cooler and dimmer patches, have been closely associated with magnetic storms on the sun’s surface. Each upsurge in sunspots reflects a slightly greater output of solar radiation and the numbers peak in roughly 11-year cycles. The next crest, or solar maximum, is expected to arrive between 2011 and 2012. According to the new study’s main prediction, East Africa should experience a major intensification in its rainy season about a year before that solar maximum.
Solar physicists cannot yet explain the 11-year rhythm of sunspots. Even so, observers have noted their cyclical waxing and waning since the first half of the 19th Century. Far more recently, satellite data have documented slight increases in the sun’s energy every time the sunspot numbers peak.
In Stager’s study, he and his colleagues compiled evidence suggesting that those solar peaks also correlate with significant up-ticks in the levels of East Africa’s Lake Victoria and other regional lakes. The widespread effect, the researchers suggested, was mediated primarily through unusually heavy rainfall that began roughly one year before each solar maximum.
“The weak part,” Stager conceded, “is we don’t know exactly why it works.”
The heightened solar energy, according to one potential explanation, heats land and ocean water alike, pushing up the moist air and producing abnormal precipitation. A more speculative hypothesis suggests that the sun’s slightly increasing energy may help trigger or pace El Niño events that bring additional rainfall to East Africa.
If supported by additional research, the study’s implications could be far-reaching. Rift Valley Fever epidemics, for example, are commonly associated with unusually heavy rainfall and all eight of Kenya’s outbreaks over the past 50 years have coincided with upward shifts in the level of Lake Victoria.
Early in the 20th Century, two successive sunspot peaks matched up almost perfectly with higher surface levels in the lake, leading many researchers to take the apparent connection for granted. At the time, however, scientists and non-scientists alike were seizing upon the peculiar sunspot cycles to explain everything from droughts to “mass human excitability.”
Then something unexpected happened. The roughly 11-year solar cycle stayed in place, but a sort of double-time pulse appeared in Lake Victoria’s fluctuating levels, making some of the lake’s peak levels coincide with minimal sunspot activity and masking the previously clear correlation.
“People took that and said, ‘Well, it was just an illusion,’” Stager said, and most scientists promptly dropped their inquiries into the purported link.
Sunspot-related phenomena have been greeted with skepticism and even hostility ever since, he said — a wariness likely not helped by murky Internet claims that the solar cycles can be linked to the dissolution of the Soviet Union, the bursting of the dot-com bubble and the downfall of Saddam Hussein.
To make their case, Stager and his colleagues first compared rainfall with lake levels to bolster past research suggesting Lake Victoria’s fluctuating levels are dictated primarily by the rain falling within its watershed, and that the water may take as long as a year or two to flow to the lake.
Using a variety of visual and statistical comparisons, the team also demonstrated a “spot-on” correlation between each sunspot maximum and Victoria’s high-water marks. The researchers found similar connections between the sunspot peaks and water levels for East Africa’s Tanganyika and Naivasha Lakes.
Because they had concluded that the lake levels are largely influenced by prior rainfall in the watershed, the researchers’ final task was to also link those rainfall amounts to the sunspot tallies. Stager pointed out that heavy rains and subsequent rises in lake levels can occur at other times, as happened during the early 1960s. But most of East Africa’s soggiest rainy seasons, he found, consistently pre-dated the regular sunspot peaks by about a year. And although the sunspot-rainfall link appeared to weaken between 1927 and 1968, Stager said his research suggests the connection held firm throughout the 20th Century.
The big question, he said, is what mechanism underlies the phenomenon. One of his chief though speculative suspects is El Niño, already associated with extra rainfall in East Africa. “We’re suggesting that the rhythm of the solar cycle might be triggering the El Niño event,” Stager said, “or setting the pace.”
He cautioned that the sunspot observations have no obvious connection to global warming, however. Nor is the solar cycle capable of providing good predictions of drought in the East Africa region. Only time, and perhaps more research, will tell if the sunspot-rainfall prognostication fares better in the coming years.