Why global warming is causing cold weather

In Why the Arctic Is Drunk Right Now Chris Mooney explains how the warming of the Arctic is impacting on the jet stream. This in turn is bringing spells of extreme hot and cold weather to parts of the northern hemisphere.

In other words, we're experiencing record-breaking cold temperatures because a wavy and elongated jet stream has allowed frigid Arctic air to travel much farther south than usual.

The article has an embedded  flash video by Jennifer Francis explaining the issue. The article also has a link to A Rough Guide to the Jet Stream: what it is, how it works and how it is responding to enhanced Arctic warming by James Mason.