Remember Mann's "Hockey Stick" graph?

[image|http://www.worldclimatereport.com/wp-images/RIP1.GIF|0|Hockey Stick Temperatures|374|536]

It's plain as day that the Northern Hemisphere temperature was pretty constant up until ~ 1900 when industrialization took off, right? Well, it's been shown that the dramatic rise in this temperature graph is an artifact of the statistical processing done on the data.

It's generally agreed that there was a "Little Ice Age" and a "Medieval Warming Period" in Europe early in the 2nd millennium AD. They're not visible in the Hockey Stick graph, but are visible in data plotted by Esper (the blue curve (Mann's curve is in red)):

[image|http://www.greeningearthsociety.org/wca/2004/images/wca15e.gif|0|Alternate Temperature History|273|600]

The obvious implication is that if the Northern Hemisphere went through a warming period and a cooling period before industrialization, and the past temperature variation was larger than initially thought, then how can we know whether the present warming is unusual or whether we are causing it?

There's much more on the problems with the Hockey Stick analysis at [link|http://www.climateaudit.org|http://www.climateaudit.org] - a site by a team that first published papers on the problems with the original paper. [link|http://www.greeningearthsociety.org/wca/2004/wca_15e.html|This] site discusses Mann's paper and subsequent analysis.

Don't get me wrong - warming of the Earth can have important consequences whether it's caused by humans or natural. And dumping increasing levels of CO2 in the atmosphere can't be a good thing. I'm an advocate of increased efficiency and investment in new propulsion and power technologies to replace burning stuff. But we need more information before we can say that "humans are causing climate change" and in order to know what makes the most sense as an approach to tackle the problem. For example, does it make sense to spend billions of dollars combating climate change if more lives would be saved developing water treatment plants and fighting malaria in the underdeveloped world? Until we have a better handle on the problem, it's really just special interests (on both sides) battling over money and influence. :-(

Ralph Cicerone seems to be an [link|http://www.calit2.net/research/labs/features/6-16-04_cicerone.html|atmospheric scientist], but to date much of the difficulty with the science by advocates has been with the mathematics and interpreting of the data. That's where careful consideration of comments by people who aren't climatologists, but know statistics inside and out, is important. Since we don't have temperature records going back 10,000 years, scientists have to use "proxies" for temperature. Care has to be used in interpreting that data (e.g. is the width of a tree ring a proxy for temperature or CO2 levels or both?).

In short, I don't think it's an open and shut case that climate change is caused by increased CO2 levels in the atmosphere since industrialization.

My $0.02.

Cheers,
Scott.