Last September, a group of scientists gathered to review the evidence on a new hypothesis: that the rapid warming of the Arctic was causing the jet stream to meander, leading weather systems to become "stuck" in places farther south, like over the United States and Europe.


If the hypothesis turns out to be true, it's a clear signal of how climate change is affecting day-to-day life in a heavily populated part of the world.



"It resonates because it brings the large changes we see in the Arctic and brings them home, so to speak," said Walt Meier, a research scientist at NASA's Goddard Space Flight Center who attended the fall meeting.

The problem, however, is that the hypothesis is so "cutting edge," said Meier, that there is not a whole lot of evidence to support it.

Still just a hypothesis—but a 'strong' one
At the meeting, proponents of the hypothesis, including its originators and supporters—researchers like Rutgers' Jennifer Francis and the National Oceanic and Atmospheric Administration's James Overland—presented data on how they believe a warming Arctic is affecting lower-latitude weather.

Other scientists, in turn, presented evidence from model studies and statistical tests showing no such linkage.

"It was a very interesting meeting because there was a great deal of debate," Meier said.

David Robinson, the New Jersey state climatologist and a researcher at Rutgers, who lead the workshop committee, said it's hard to find statistically significant signals in part because dramatic Arctic sea ice loss has only been going on for a short period of time, since 2007.

"It's clearly not nearly long enough a record to be able to identify any linkages in a statistically significant sense," he said.

Robinson believes the hypothesis is a strong one. "I think Jen Francis presents incredible evidence," he said.

But the way that science works is that someone puts forth an idea, and then "everyone has at it," he said.

Arctic signal can be hard to read


Since such a hypothesis will be difficult to prove using only data from observations, models can also play a role, said Clara Deser, a scientist who heads the Climate Analysis Section within the Climate and Global Dynamics Division at NCAR.

"Then we can do our experiments where we tinker with the sea ice and look at where the wind patterns and the weather patterns respond," she said.

Deser, who also attended the September meeting, said she is now working on setting up some model experiments with researchers at the United Kingdom's Met Office Hadley Centre and the Canadian Centre for Climate Modelling and Analysis.

As the report summarizing the meeting pointed out, because weather in the mid-latitudes is so variable and is affected by so many factors, teasing out a signal from the Arctic could prove difficult.

The tropics also influence weather in the middle latitudes, and a number of other climate oscillations can also play a role.

Looking beyond a single cause
In a schematic included in the meeting report, numerous arrows flow in and out between the Arctic and the mid-latitudes, highlighting just how complicated a problem this is.

Looking for one primary cause to explain a weather event will always be problematic, said Deser, because the system is so complicated.

Nonetheless, every time there is an extreme weather event, the question of climate change "always gets asked," she said.

"We are always wanting to find a single cause for our weather events. And I think that the real world is very complicated," Deser said.

This winter was no exception. As cold weather and record snow pummeled the East Coast, some wondered if the frigid temperatures could also be due to the meandering jet stream, pushed by a warmer Arctic.

In February, several leading climate scientists wrote a letter, published in Science, addressing that very question.

"Some have been touting such stretches of extreme cold as evidence that global warming is a hoax, while others have been citing them as evidence that global warming is causing a 'global weirding' of the weather. In our view, it is neither," the letter read.

In other words, the frigid winter weather was just that: weather.

As to whether scientists can link the next big heat wave or weeklong storm system to a warmer Arctic, at least for a few more years, the jury on that is likely to remain out.
