All right, so a heavy snowfall in England and Wales is unusual before Christmas, but, as Marcus Brigstocke drove home in his typically confrontational fashion on the latest "Now Show", what is happening on ones own doorstep is not indicative of the rest of the world. Global temperatures are continuing to rise, as the Weather Club and web sites like this indicate.
There was a time, as people of my generation will remember, when there was some snow every winter, sometimes at least as severe as the current situation: early 1963, for instance, or 1947/48 when the opposition attacked the government for lack of preparedness. Some things do not change.
Paradoxically, one of the predictions of climate scientists is that, as the North Atlantic warms up, Britain will get cooler in winter because the Gulf Stream/North Atlantic Drift will move westwards as the Greenland ice sheet retreats. This particular bad winter for us is down to La Nina and fluctuations in the jet-stream as I understand it, but perhaps we had better prepare for more frequent severe winters in future as well as hotter springs.
As to how far global warming is caused by man - well, that's another matter.
Update 2010/12/27: Another contributory factor is said to be the loss of ice-cover in north European seas, as reported in this Independent article: