Weather in Toronto has recently taken a cold turn. Given the recent release of the First Working Group / Fourth Assessment Report of the IPCC, the joke du jour has become "What's all this fuss about global warming?" This bothers me for two reasons.
First, I feel it's heedless to joke about what is, by general consensus of the scientific community, a serious problem. It betrays a simplistic, "out-of-sight out-of-mind" naïveté. By analogy (here I corroborate Godwin's Law), consider how foolish they felt in 1945 who said, in 1940, "Holocaust? What Holocaust?"
Secondly—humour me for a moment while I indulge in some wildly speculative and baseless hand-waving—'more frequent extreme weather' is among the commonly listed effects of climate change. A 2006 IPCC report quoted in the Wikipedia article states:
The climate system is a coupled non-linear chaotic system, and therefore the long-term prediction of future exact climate states is not possible. Rather the focus must be upon the prediction of the probability distribution the system’s future possible states by the generation of ensembles of model solutions.
For the non-technical, consider a gross oversimplification in the form of a ball suspended by a spring. The increase in global temperature corresponds not to a higher or lower resting state for the ball, but an increase of energy in the ball-spring system, a "bouncier" state. A system with more energy has more frequent and more extreme states - the ball will reach higher peaks and lower troughs more frequently than it would in a less energetic system.
In the more complex system of the atmosphere, the connection is less obvious. For this reason the newspapers often equivocate: "Hurricane Katrina was possibly, but not definitely linked to climate change…" Regardless, more floods and simultaneously more droughts are being reported in many areas. 'Freak' weather events in the news have become more destructive, and insurance companies (earning their keep on being neither optimistic nor pessimistic) are trading climate futures to offset expected losses due to natural disasters.
The entire climate is more volatile, which brings me (at last) to my point: What is to suggest that cold weather disproves global warming? If we have four warm winters and one brutally cold winter (or four warm winter months and one brutally cold month) the average temperature may barely increase. However, fifty or a hundred years ago, we would have had five consecutive, wholly unremarkable 'average' winters. Consider, on January 20, 2005, the temperature was -17°C. On the same day in 2006 it reached 10°C, while the mean is -8°C. It's only one data point, and you may dismiss my view as apocalyptic, but if extreme weather is a harbinger of climate change then it is ridiculous to suggest that a cold snap means we have nothing to worry about.