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US shivers as extreme cold invades, but is this climate change?

TAMPA: An Arctic-like deep freeze gripping much of the United States with double-digit subzero temperatures is the coldest of its kind in 20 years, but is it connected to local weather exchange?

Experts say it could be, but whether or not global warming plays a role in this explicit extreme weather phenomenon remains to be up for debate. Here's why:

"It is a mass of very cold air that typically sits right on the North Pole and tends to be restricted to the North Pole by the jet stream," defined Ben Kirtman, professor of atmospheric sciences at the University of Miami Rosenstiel School of Marine and Atmospheric Science.

Normally, the jet flow — which is a robust a current in the atmosphere — would keep this chilly air in the Arctic, but when the jet flow wavers, or weakens, the chilliness can spill.

"Occasionally we get meandering of the polar vortex and that is what is happening right now. And if you get a real big one you can have a big blob of cold air penetrate very far south," Kirtman informed AFP.

According to the Weather Channel, this week's freeze "may be the coldest in more than 20 years in parts of the Midwest and will smash dozens of daily record lows in some areas."

NASA's Earth Observatory stated that steady northwest winds "were likely to add to the misery, causing dangerous wind chills below -40 Fahrenheit (-40 Celsius) in portions of 12 states."

The National Weather Service warned that a wind sit back of -20 F could cause frostbite in as little as 30 mins.

"It is not out of bounds with the historical record. They happen. You get storms that are bigger than other storms. There is a big part of this that is part of the natural variability of the climate," stated Kirtman.

The protective band in the atmosphere that typically keeps polar air in the north can and does waver. That, too, is not sudden.

"There are always undulations in the jet stream," stated Kirtman.

The power of the jet flow is connected to the temperature distinction between the recent tropics and the frigid poles.

The starker this distinction, the stronger the jet flow, and in principle, the much more likely that the polar air will stay in the Arctic.

However, from time to time a jet flow that is too strong can also become unstable, "and these instabilities cause a certain amount of waviness in the jet so you can get these meanders," stated Kirtman.

Some evidence also suggests that once the poles heat up, there may be much less distinction between the tropics and the poles, and that, too, can make the jet flow become wavier, permitting chilly air to spill down from the north.

The Arctic is well known to be heating at two times the rate of the remainder of the planet.

"What people are starting to ask is, if you weaken the jet stream, does that mean we are going to have more, stronger excursions of the polar vortex? If that turns out to be true, we can link more extreme cold spells to climate change," Kirtman added.

Researchers are inspecting knowledge in the quest to find out.

"There are some hints that it is linked to climate change, but I would emphasize that the jury is still out," he stated.

Scientists are getting better at interpreting the role of local weather exchange in sure weather extremes. So far, the alerts are clearest in occasions like rainfall, drought, heatwaves and wildfires.

But when it comes to chilly snaps, the answers don't seem to be as transparent.

"I would say the science is still incomplete. We don't have proof at this point," stated Kirtman.

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