Sauce for the gander on Global Warming

As I sit here with our heater out, occasionally feeding more wood into the wood stove and sipping coffee, I see yet one more article reminding us that, in the case of cold weather, we cannot use it as evidence against Global Warming, although, of course we are free (indeed, it seems, obligated) to use warm weather as evidence in favor of it:

People across the northern hemisphere are facing the fact that a warming planet doesn't get rid of winter. The woes extend far beyond Britain's extended snow and chill. On Monday the heaviest snow on record plastered Seoul. Later this week the central US will experience its most brutal cold wave in 10 to 20 years. And most of western Europe will be encased in a deep freeze by this weekend.

In any given year, there could be a season as shocking as Britain's epic winter of 1962-63 – when snowdrifts were measured in metres, and temperatures stayed below freezing for most of January – or the summer of 2003, when tens of thousands died in some of the worst heat ever recorded in Europe.

What's different now is that climate change is shifting the odds towards record-hot summers and away from record-cold winters. The latter aren't impossible; they're just harder to get, like scoring a straight flush on one trip to Vegas and a royal flush the next.

The point seems to be that one swallow does not a summer make--or maybe we should say "one snowflake does not a winter make." It's not an illegitimate point, but why is it that whenever we see a snowflake we are reminded of this, but whenever there is a swallow a summer is considered to have been made?

HT: Roger Pielke