- There has been a statistically significant increase in average global temperature, with fits and starts, over the last 150 years although this has levelled off in the last 10-15 years.
- There is a correlation with increased CO2, however it doesn't track perfectly and from what we know of the physics of CO2 radiative forcing it is both logarthimic (as we produce more, the effect gets relatively less for each additional unit) and that, to account for the warming seen, additional poorly understood 'feedback' mechanisms must be invoked.
Somewhat as an aside I thought this quote from Stephen Schneider, an arch IPCC supporter, was almost entirely agreeable. Although no doubt people can point to many things he has said as entirely disagreeable, it is worth praising statists when they do get it right:
The transportation sector is the fastest-growing and seemingly most intractable source of carbon emissions precisely because it is the most socialized, subsidized,120 and centrally planned sector of the U.S. economy—at least for favored modes like road transport and aviation. It has the least true competition among modes, and the most untruthful prices, with hidden costs of hundreds of billions of dollars per year for U.S. road vehicles alone.121 These distortions leverage more billions into otherwise uneconomic infrastructural and locational decisions. In particular, the dispersion of uses that causes so much excessive driving is mandated by obsolete single-use zoning rules meant to segregate noxious industries that scarcely exist today. Congestion is specifically caused by non-pricing or underpricing of the road resource: most roads are supported by taxes, not users, so they look free to drivers who behave much as Soviet customers did in demanding a great deal of energy when it looked free. Congestion is not only unpriced, but is further exacerbated by building more subsidized roads that elicit even more traffic, and by requiring developers to provide as much parking as people use when they pay nothing for it. Future generations will marvel that the incredible social costs of these policies—costs intertwined with many inner-city ills—went so long uncorrected: all ways to get around, or not to need to, were never made to compete fairly against each other, and drivers neither got what they paid for nor paid for what they got.
I have always thought that both sides of this debate should consider the alternative scenarios; what would libertarians do if man is proved to be warming the planet?; what would AGW proponents do if there is global warming, but it is entirely natural?; is natural always a good thing?
Hopefully 'climategate' has opened the door to honest debate.