Needless to say for anyone who has even a rudimentary knowledge of the difference between climate and weather, a few days of cold weather in winter doesn't disprove global warming any more than a few days of hot weather in summer proves it. Weather is weather, and nothing in global warming science says that winters will suddenly become balmy tropics every year. Climate change is all about the trend in global averages over time. And while the United States was experiencing record-breaking cold, Australia and New Zealand were experiencing record-breaking heat. Right now the planet is - on average - warmer than normal. That doesn't make the United States feel any warmer (especially with the wind chills), but it does help put extreme weather events into context.
In September 2013 the Intergovernmental Program for Climate Change, called the IPCC by friend and foe alike, released the latest update in its series on the state of our climate. The first volume addresses the Physical Science Basis of climate change. You can read the full 2,216-page report, or scan the 33-page Summary for Policymakers.
The IPCC concluded that "warming of the climate system is unequivocal." They note that "atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased."
The IPCC also concludes that "it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." ["Extremely likely" is defined by the IPCC to be 95-100% confidence]
So climate change is happening, and human activity is the main driver. Baby, it may be cold outside (after all, it is winter), but we are warming our planet. In fact, the dynamics of that warming may be why the polar air has vortexed it's way down to the United States instead of staying where it should be, up at the north pole.
As we move forward, we'll talk more about the challenges of communicating man-made global warming to the public in the face of the annual parade of politicians rushing to call climate change a "hoax" every time it snows. It's a huge challenge, but it's critical for the future of all of us in the global community that policymakers take responsibility for addressing a scientific issue that will only continue to become more acute the longer we choose not to take action.