This winter in the Arctic has been dramatically different from the season we’ve experienced so far much of the central and eastern U.S., and it’s fueling an equally dramatic debate within the scientific community about climate change and whether global warming is playing a role – or not.

Across the Great Lakes, striking images have been captured of near-record amounts of ice covering the lakes’ surface, especially in places like Lake Superior’s Apostle Islands National Lakeshore, whose majestic shoreline ice caves opened recently for the first time in five years.

Nearly 90 percent of the Great Lakes has been covered in ice thanks to this year’s bitterly cold winter, a number that’s up dramatically from last year’s ice cover maximum of 38.4 percent and way up from 2012’s cover, which reached a maximum of just 12.9 percent.

But in the Arctic, ice amounts have followed the opposite trajectory as this winter has brought record low amounts of sea ice, the kind that grows and retreats seasonally every year in response to warming (or cooling) air and ocean temperatures.

On Feb. 18 – during the month when it normally reaches its highest amount for the year – Arctic sea extent measured about 8.93 million square miles, down roughly 7,000 square miles from the previous record low for the same date since satellite measurements began in the late 1970s.

Much warmer-than-normal Arctic temperatures are believed to be the main cause, as temperatures during the first half of February ranged from 7.2 to 14.4°F above average across the polar region.

This illustration, created by the Boulder, Colo.-based National Snow and Ice Data Center, shows how this February’s Arctic sea ice looks compared to the 1981-2010 average:

Changes in the jet stream due to climate change?

To scientists like Dr. Jennifer Francis, a research professor at Rutgers University’s Institute of Marine and Coastal Sciences, the reason why this is happening – why unusually warm conditions in the Arctic can occur at the same time there’s record cold at lower latitudes – likely lies in the jet stream.

This fast-moving river of air – which flows high above the Earth’s surface and marks the boundary between cold, polar air to the north and warm, moist tropical air to the south – drives the weather we experience in the middle latitudes, the region in which the U.S. lies.

Over the past few decades, the Arctic has warmed at a much faster pace than the rest of the planet, resulting in dramatic losses of summertime sea ice. With more open water that absorbs sunlight (rather than ice, which reflects it), the Arctic Ocean in turn stores more heat.

Francis’s research suggests that as the Arctic gets warmer, and the temperature difference between the North Pole and the equator gets smaller, the jet stream’s west-to-east winds get weaker. “As those winds get weaker, the jet stream tends to take a wavier path, more northward and southward around the Northern Hemisphere,” she explained in a conference call last week.

Why is this important? Because when it moves more in a north-south direction, the jet stream’s waves get bigger and slower, she added. “And so the weather they create also moves more slowly, and it tends to feel like on the surface that we’re in a pattern that just seems to get stuck.”

This would seem to explain why weather events like this year’s persistent cold spells across the eastern U.S. have lasted so long. Though Francis is careful to add that “we can’t say the rapidly warming Arctic caused this pattern this year,” she says it’s “a great example of the kind of pattern we can expect to see happen more often as the globe, and the Arctic in particular, continue to warm.”

‘Highly controversial’

Francis’s ideas linking what happens in the Arctic to what happens further south caught fire in the media, as they suggested that global warming could cause extreme cold events by changing the jet stream so that it could pull frigid polar air from the Arctic southward.

Even John Holdren, President Obama’s science advisor, said as much in this January YouTube video, explaining the polar vortex:

However, this view is “highly controversial” and “not very convincing” according to the University of Exeter’s Dr. James Screen, who is leading a three-year project to study the impacts of climate change in the Arctic on the middle latitudes.

Studies show large disagreement in how Arctic sea ice loss impacts the jet stream, he said in an email interview with weather.com, adding that “it is impossible to attribute any single event to climate change.”

Pointing to the floods that have swamped the U.K. this year, Screen said there is evidence to suggest certain kinds of extreme weather will become more likely in the future, such as more intense rainfall thanks to more water vapor in the atmosphere.

“What is harder to predict is how the atmospheric circulation will change, for example the storms or the jet stream,” he added. “So whilst more intense rainfall is consistent with expectations under climate change, the exact contribution of human activities to this winter’s rainfall is unclear. In the case of the cold winter in the U.S., this is harder to explain due to climate change.”

That’s a view shared by Dr. Kevin Trenberth, a scientist with the National Center for Atmospheric Research who co-authored a Feb. 15 letter in the journal Science that noted cold air outbreaks “even more severe than occurred this winter” hit the U.S. in the 1960s, 1970s and 1980s – “back when the Arctic sea ice was thicker and more extensive than it is today.”

Role of natural variability ‘very strong here’

There’s a likelier explanation for the changes in the jet stream, Trenberth added. It’s the phenomenon known as the Northern Annular Mode, which shifts “from stronger westerlies and a stronger jet stream to one where there’s much weaker westerlies and a much weaker jet stream.

“It’s a highly natural mode in the atmosphere, it doesn’t require changes in sea surface temperatures or the Arctic, or the sun or anything else to activate it,” he added. “Whether the Arctic or anything else nudges it in a particular direction or not remains to be seen. But the role of natural variability is I think very strong here.”

With too many other possibilities like this – and because scientists are more sure of global warming’s impacts on things like heat waves, drought and precipitation patterns – James Overland, an oceanographer with NOAA’s Pacific Marine Environmental Laboratory, agreed that “it’s very hard to prove” a connection between the jet stream and the Arctic.

“If you look at it over the last 20 or 30 years, you really don’t see a long-term change with more connection to the Arctic,” he added. “But if you look at the last five years, and you look at some of the possible physics … you can’t prove there’s a connection, but you can’t rule it out yet.”

That’s because the Arctic is changing faster than anyplace else on Earth, with temperatures rising there two to three times faster than lower latitudes. “If it was proven that Arctic warming is or will impact mid-latitude weather, then this would have profound implications,” said Screen. “But at the moment that link is far from clear.”

The key message at the moment, he added is that “the climate system is very complex and we still don’t fully understand if and how the jet stream is changing due to global warming. Warmer and possibly wetter winters are the general expectation in a warming climate, but natural variability will continue cause extremes of all kinds.”

A similar note was sounded by the five co-authors of the Feb. 15 letter in Science: “Even in a warming climate, we could experience an extraordinary run of cold winters,” it concludes. “But harsher winters in future decades are not among the most likely nor the most serious consequences of global warming.”