Freak Winter Weather: Fluke or Fuel in Warming Debate?

James Owen
National Geographic News 18 Mar 08;

Freak winter weather has struck almost every area of the Northern Hemisphere with bizarre extremes in recent months.

Snow fell on usually sweltering Baghdad and paralyzed central China, while the season barely registered in Scandinavia, where some countries have seen the warmest winter in centuries.

The unusual season seems to be the result of a "perfect storm" of weather patterns occurring at once, experts say.

But what does this mean for the debate about global warming?

Balmy Arctic, Snowy Middle East

Meteorologists in Sweden this month reported the country's mildest winter since record-keeping began in 1756.

Neighboring Finland also registered its warmest winter on record, with average temperatures about 9 degrees Fahrenheit (5 degrees Celsius) higher than average. And Arctic Norway is heading for its mildest winter since monitoring started more than a century ago.

Meanwhile, in the United Kingdom, bluebell flowers bloomed in February for the first time, according to London's Natural History Museum. The plant usually flowers in April and May.

But elsewhere in the Northern Hemisphere, the winter has been notable for its severity.

Snowstorms paralyzed central China in January. At least 60 lives were lost and some 5.8 million people were left stranded at train stations nationwide (see photos of China's blizzard).

Blizzards also hit the Middle East the same month, blanketing the region in rarely seen snow. Many residents of Baghdad, the Iraqi capital, saw their first snowfall, according to reports.

Swaths of North America, meanwhile, suffered their heaviest snow since the 1960s.

Last month, much of the northeastern United States was buried under 2 feet (0.6 meters) of snow. New York's Central Park saw its biggest single snowfall—26.9 inches (68 centimeters)—since records started in the 1860s.

These chilly events appear to be supported by the latest global climate data.

Climate research centers including the U.K.'s Hadley Centre for Climate Prediction and Research, and the Goddard Institute for Space Studies in New York, noted an average drop in global air temperature of 1.15 degrees Fahrenheit (0.64 degree Celsius) over the past year.

Are skeptics of climate change seizing on this season as evidence that global warming might not be happening?

Global Warming Skeptics Respond

Well-known global warming doubter Robert Balling, a climatologist at Arizona State University, is guarded in his response to the unusual weather.

"While the trend is surprising, given no volcanic eruption [occurred to block sunlight and cause a global cool-down], I doubt the trend is statistically significant at this time," he commented.

"We both know that if we had seen a jump upward [in temperature], the global warming advocates would have had a field day," he added. "I find the skeptics to be far more cautious."

Fellow skeptic John Christy, of the Earth System Science Center at the University of Alabama in Huntsville, is indeed cautious.

The drop in global average temperature between January 2007 and January 2008 is most likely due to a shift from a minor El Niño warming event to a substantial La Niña cooling event, Christy said in an email.

La Niña is a natural weather system linked to unusually cool sea temperatures in the equatorial Pacific Ocean. El Niño, which has the reverse climatic effect, is characterized by much warmer Pacific temperatures.

The two alternating phases are usually separated by periods of one to three years, but the current switch occurred without an interval, accounting for the steep temperature swing, Christy explained.

"Regional weather conditions have large variability from year to year, especially in the northern hemisphere winter," he said.

"There is likely a small amount of the La Niña effect in the weather patterns in the northern latitudes, but a good bit is more likely [due to] the natural variations," Christy added.

"Someone, somewhere experiences a record high or low almost every winter."

The debate over human-caused global warming deals not with year-to-year variations but with slower changes occurring over decades, he said.

"Overall the global temperature trends we find are at the lowest warming rates among all of the projections by the array of models used in the [UN Intergovernmental Panel on Climate Change reports]," Christy added.

Temperature Swing

As for the balmy conditions experienced in northern Europe, these are likely due to the influence of the North Atlantic Ocean, according to Simon Boxall of the National Oceanography Centre in the U.K.

Known as the North Atlantic Oscillation, the weather system is controlled by pressure systems over Iceland in the north and the Azores islands, west of Portugal, in the south.

"At the moment we've got relatively strong low-pressure systems over Iceland and highs over the Azores," Boxall said.

"That effectively channels [warmer] water over to northwest Europe," he said. "It also tends to draw in warmer, drier air from the sub-Sahara [region of Africa]."

The contrasting weather extremes in Europe and North America this winter "are not an indication of climate change," he said.

"Taking one year's worth of data as proving climate change either way is scientifically extremely dodgy," Boxall added.

But, he said, "I don't think there are any scientists working on studies of how climate is changing today who refute the fact that the climate as a whole is getting warmer."