Jet stream shift 'could prompt harsher winters'

A warmer Arctic could permanently affect the pattern of the high-altitude polar jet stream, resulting in longer and colder winters over North America and northern Europe, US scientists say.
The jet stream, a ribbon of high altitude, high-speed wind in northern latitudes that blows from west to east, is formed when the cold Arctic air clashes with warmer air from further south.
The greater the difference in temperature, the faster the jet stream moves.
According to Jennifer Francis, a climate expert at Rutgers University, the Arctic air has warmed in recent years as a result of melting polar ice caps, meaning there is now less of a difference in temperatures when it hits air from lower latitudes.

"The jet stream is a very fast moving river of air over our head," she said yesterday at a meeting of the American Association for the Advancement of Science.
"But over the past two decades the jet stream has weakened. This is something we can measure," she said.

As a result, instead of circling the earth in the far north, the jet stream has begun to meander, like a river heading off course.
This has brought chilly Arctic weather further south than normal, and warmer temperatures up north. Perhaps most disturbingly, it remains in place for longer periods of time.

The United States is currently enduring an especially bitter winter, with the midwestern and southern US states experiencing unusually low temperatures.
In contrast, far northern regions like Alaska are going through an unusually warm winter this year.