2010 set world records for weather extremes

From freezes in South Florida to deadly heat waves in Russia, 2010 broke records worldwide for flooding, heat, cold and snow, fueling concerns that a warming planet is starting to cause significant weather disruptions.


The year's extreme weather should serve as a warning, scientists say, a glimpse of a future in which a shifting climate is likely to spawn many more dramatic changes in the daily weather.

"Heat waves and extreme flooding events are increasing in the U.S. and that's consistent with what we know about climate change," said Deke Arndt, chief of climate monitoring for the National Oceanic and Atmospheric Administration's National Climate Data Center.

Yet climate scientists are quick to add that no single weather event can be tied to climate change. While the Earth is warming and increases in extremes documented in the U.S., the Earth's weather is too variable and some of the extremes so pronounced that climate change alone cannot explain them now.

To document climate change, scientists point to trends, such as the increasing frequency of days that break heat records and increases in heavy rainfall and snowstorms in certain regions.

In the U.S., the biggest red flag was the lack of cooling at night during the summer months, Ardnt said.

Overnight lows stayed much warmer than usual over about 60 percent of the nation during parts of June, July and August. Typically only about 10 percent of the country would experience such persistent warmth.

"It's not as dramatic as a snowstorm or hurricane, but statistically, that slaps you in the face," Ardnt said.

The year brought more extreme events than normal, but not an unprecedented amount, said Ardnt, pointing to 1998 -- the year of California floods -- and 1934 -- remember the Dust Bowl? -- as the most extreme weather years for the U.S.


Why so hot?

Global heat throughout the Northern Hemisphere summer reached record extremes, said Klaus Wolter, a research associate with NOAA's Earth System Research Laboratory and the University of Colorado in Boulder. It was more than eight times hotter than what scientists would expect from natural variation, and so warm that the Moscow heat wave that led to 15,000 deaths contributed little to the overall record.

"This summer really was off the charts. The big question, of course, is how did this come about?" Wolter said.

El Niño -- warmer-than- normal seas in the tropical Pacific -- contributed somewhat, because it tends to push warmer air around the globe. But El Niño faded by spring, to be replaced by its opposite, La Niña.

Probably the most significant contributor to the extraordinary heat was the Arctic Oscillation and North Atlantic Oscillation, two weather trends that act in tandem.

In January and February, the oscillations moved sharply toward the warm side, as high pressure reached record levels over Arctic. High pressure and warmer-than-normal temperatures over the Arctic trigger big changes in global weather. One effect is to squash the tradewinds over the tropical Atlantic. The tradewinds keep the Atlantic cool.

So when high pressure over the Arctic reached unprecedented extremes in early 2010, the tradewinds shut down and the Atlantic climbed to record-breaking temperatures that persisted throughout the year.

For Florida, the hotter seas made hurricanes form further east, which may have contributed to the storms' fizzling out before they reached land, Wolter speculated.


A freezing Florida
The Arctic high pressure did much more than help the Atlantic heat. It froze Florida and, combined with El Niño moisture, dumped record-breaking snow on the nation's capital.

Shrinking sea ice, another symptom of a warmer planet, could be influencing the extreme high pressure over the Arctic, according to Jennifer Francis, research professor in Atmospheric Sciences at Rutgers University.

Francis studies how changes in the Arctic can drive global weather patterns. Theories about the influence of sea ice are up for debate, but a growing body of research has demonstrated potential links.

As the sea ice diminishes, the Arctic warms more into the fall and winter, Francis said. As the Arctic warms, the temperature difference between the North Pole and the equator shrinks.

"That temperature gradient is what drives the jet stream," Francis said.

The winter hallmark of high Arctic pressure is a weak jet stream. The jet stream drives weather systems around the Earth and is usually strong enough to hold Arctic air to the polar region. But when it slackens, frigid air escapes south. Last winter and a few weeks ago, the jet dipped so far south that it blasted Florida with freezing temperatures.

As the Arctic warms and ice continues to shrink, Francis theorizes, the South will see more episodes of extreme cold.

A future of extremes
Areas prone to heat waves will see more of them in a warmer climate, said Martin Hoerling, research meteorologist with the NOAA Earth Systems Research Laboratory in Boulder, Colo.

But that doesn't mean a warmer globe was responsible for the heat waves that scorched the Northeast in 2010 or the deadly heat wave in Moscow.


In the past decade, the annual average temperature on Earth has steadily increased compared with the historic average between 1951 to 1980. The spike ranges from a little more a half a degree in 2000 to nearly 1.2 in 2010, a new record.

However, a one-degree increase in global temperature cannot explain the year's crazy weather. The amount of warming amounts to noise, compared with other, natural variables in the weather, such as the Arctic Oscillation and El Niño.

If a warmer globe had any effect on the Moscow heat wave it was small, likely less than 10 percent of the total influence, Hoerling said.

But as the globe transitions to a new climate, weather extremes, such as the Moscow heat wave, will become more common, most scientists agree.

It is like the often-stormy transition between seasons -- think of spring to summer, only on a larger scale.

"The climate is in the process of transitioning to a new state," said Jeff Masters, founder and director of meteorology for Weather Underground. "I worry that this year is a sign that we're starting to see some of that instability."

By Kate Spinner

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