Big Chill vs. Global Warming: What's Going On?

LiveScience.com

The recent, rare snow in Jerusalem and parts of Lebanon, along with freezing temperatures for Southern California have not nixed the reality of climate change. The planet is warming, and chilled weather doesn't negate that fact, say climate experts.

In fact, such "rare" storms are expected in a warming world.

"As the globe warms, regions of the Earth that have cold winters will still have cold winters, and we will still see the random rolls of the weather dice, like we are seeing this winter," climate scientist Michael Mann of Pennsylvania State University told LiveScience. "But climate change is loading the weather dice, so that 'sixes' are becoming more common, and 'ones' are becoming less common."   

No single weather event can be pegged to climate change, which is a long-term trend that over time affects weather, and it affects the weather in different regions in different ways. Rather, as the planet warms, the chances of an extreme-weather event, including very large snowfalls, increase. That is, the dice are loaded for extreme events. [The Reality of Climate Change: 10 Myths Busted]

"Climate is the statistics of weather over the long term," Ken Caldeira, a senior scientist at the Carnegie Institute for Science at Stanford University, told LiveScience last year. "No specific weather event can by itself confirm or disprove the body of scientific knowledge associated with climate change."

Global warming with a side of chill

A big chill crept over California this weekend, with temperatures in a San Diego county dipping to 23 degrees Fahrenheit (minus 5 degrees Celsius), breaking a record set in 2007. And, according to news reports and the National Weather Service, San Diego beaches may have gotten a coating of morning frost, while a freeze warning remains in effect until Tuesday morning for the San Joaquin Valley.

Meanwhile, a storm system dumped 4-6 inches (10-15 centimeters) of snow on Jerusalem last week, killing at least eight people. And sleet and freezing rain will stretch across parts of the Southeast today and Tuesday, according to weather.com. [The World's Weirdest Weather]

Amidst the chilly headlines, however, Earth continues to break heat records left and right. "It's easy to cherry pick and find places that might be unusually cold at any given time, for example Southern California right now," Mann told LiveScience in an email. "But meanwhile, daffodils are coming up in Cincinnati.

"Over the past decade, we have seen daily records for all-time warmth broken twice as often as daily records for all-time cold," Mann wrote. "The year 2012 had the highest ratio we have ever recorded, more than four to one. That's like 'sixes' coming up four times as often as 'ones.'"

Here's how cold temperatures and snowfall can abound in some regions while the Earth warms: Warm air holds more moisture than its cold counterpart. That means if the temperature is low enough, "those warmer winters will counter-intuitively favor larger snowfall events," Mann explained.

And modest cooling is expected to result from global warming in some regions. For instance, Mann explained, models forecast a slowdown of the warm, poleward-moving ocean current in the North Atlantic, a slowing that will modestly cool that part of the ocean.

Most of Earth getting hotter

"But these are highly seasonal and regional effects," Mann said. "The vast majority of the globe will warm substantially over the next century, likely with profound negative consequences, if we continue to heat the planet by increasing greenhouse gas concentrations through fossil-fuel burning."

In fact, at least in the United States, 2012 was the hottest year on record, smashing the previous warmest year, 1998. And the past decade set itself apart in terms of extreme weather, from heat waves and drought to flooding, something scientists say can be, in part, attributed to climate change.

"It is very likely that several of the unprecedented extremes of the past decade would not have occurred without anthropocentric global warming," study researchers wrote in the March 25, 2012, issue of the journal Nature Climate Change. In that study, two scientists reviewed extreme weather events going back to 2000 as well as research into possible connections with global warming.

Since 1950, human-caused climate change seems to have brought on more extreme weather, with even more such extremes expected this century, reported the Intergovernmental Panel on Climate Change, the international body charged with assessing climate change, in 2011.

So far this year, the United States has set 630 records for highest maximum temperature versus 114 records for lowest minimum temperature, according to the National Climatic Data Center.

"When you step back and look at what is happening overall, it is very clear that we are seeing overall warming, and a dramatic increase in record-breaking heat around the world," said Mann, pointing out the record heat and wildfires happening in Australia right now and the record heat experienced in the United States this past summer.

"They are both symptomatic of the perceptible and profound impact that climate change is already having on our weather," Mann added.

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