They describe a new paper by Von Storch et al. that was published in a recent (September 30th) issue of Science. The German journal Der Spiegel (The Mirror) made an interview with Von Storch on October 4th, 2004. Von Storch said something along these lines:
- The assumptions that have led Mann, Bradley, and Hughes (MBH) to their "hockey stick graph" in 1998 and 1999 are unacceptable. Their method is wrong - in fact, it's rubbish.
That's a blunt formulation and one is naturally cautious about it, but it seems that this formulation is justified. It may be useful to say what the "hockey stick graph" means. Try to draw the graph of the "global temperature" as a function of the date - between the years 1000 and 2004. What graph will you choose if your results are supposed to support the statement that the world economy and our breathing should be slowed down because these processes create too much carbon dioxide which leads to an unacceptable and unprecedented global warming?
Well, of course, you will draw a constant function between the years 1000 and 1900 (long, stable shaft) and a quickly increasing temperature between 1900 and 2000 (it's the blade of the hockey stick). Such a profile will prove that the changes are caused by the humans, and they are undisputable and potentially disastrous. That's roughly what MBH did, and they became famous for their result. Their graph was reproduced by the global climate committee of the United Nations (IPCC, Intergovernmental Panel on Climate Change) and it became one of the justifications of the process that culminated with the Kyoto protocols.
Of course, MBH also had a scientifically impressive method based on the principal component analysis. It was really the paper by Ross McKitrick and Stephen McIntyre - the so-called "audit of MBH" - that helped me to understand the methodology of MBH a bit better. I've already written an article in which I stated my opinion that this method may be a good one to isolate a picture that is covered by dust, but in order to estimate the past temperatures from shaky proxy data, it may be better to simply take the average of all the known data - the same average that the kids learn when they're 8 years old. It seems that this simple opinion is becoming more influential.
Von Storch et al. showed that the method of MBH is suspicious, using a kind of sensitivity test. In fact, I would say that MBH themselves should have done such a sensitivity test before they published their paper. How did Von Storch et al. do it? They simulated an artificial world, and extracted the fictious "proxy data" (the widths of tree rings etc.) from this model, and added a reasonable amount of random noise. In their virtual world, they knew perfectly what the "true temperatures" should be. Afterwards, they inserted the "proxy data" to the formula of MBH, and used that formula to reconstruct the temperatures. The result was very different from the "true temperatures". Quite generally, the method of MBH seems to reduce the temperature fluctuations in the past (before the thermometers were known).
What does it mean? Well, most honestly, it means that we know very little about the historical temperature record. However, if the fluctuations were greater than what MBH argued (by a factor of two or more), then the temperature growth in the 20th century is not so exceptional. People used to think that there was a medieval warm period (MWP), followed by a little ice age, and these old theories may stage a comeback.
The importance of the carbon dioxide
I've never understood the hysteria behind the concentration of CO2 in the atmosphere. CO2 is an important gas - it's produced when we breath, and it's necessary for photosynthesis. Animals produce it, plants consume it. The existence of CO2 proves that there are either animals, people, or machines around, and the growth of the concentrations of CO2 is known to be correlated with the growth of the gross domestic product (GDP). Well, CO2 may be used as one of the indicators of life and working economy.
Is it a poison? Well, I don't think so. CO2 is not quite the same thing as Mercury, for example. ;-) Should we really worry if the human civilization doubles the concentration of CO2 in the atmosphere? Today, the concentration is below 400 ppm ("parts per million"), which means less than 0.04 percent. The concentration of CO2 in your bedroom is probably much higher. Does it really matter whether the concentration in the atmosphere is 0.03 or 0.05 percent? Should we pay trillions of dollars just to avoid this increase, even if we don't know any clear negative consequences of such a growth?
Well, CO2 is known to protect the Earth from cooling, it's a greenhouse gas. Well, it's not the only greenhouse gas, and on the other hand, there are also other compounds in the atmosphere that tend to reduce the temperature (aerosoles, for example). We may ask a simple question: Is it better to heat the planet up, or to cool it down? Imagine that an observable called "the global happiness" is a function of the "global temperature". An interesting question is what's the derivative of "happiness" evaluated at the current temperature. If it's zero, than up to the first order, it does not matter whether the temperature goes up or down. If it's nonzero, there is 50% probability that it is negative, and 50% probability that it's positive. The expectation value of Delta(happiness) is zero. But of course the expectation value of "Delta(happiness) squared" is positive, and it grows with "Delta(temperature) squared". Do you think it is reasonable to pay 1 percent of your GDP for the chance that Delta(happiness) squared is likely to be a bit smaller, even though you can't predict the sign of Delta(happiness)?
I think that such a decision is an economic stupidity, especially because I tend to think that the derivative of the happiness with respect to the temperature is positive. ;-)
There are many other things whose concentration increases drastically as a result of human activity. The Aliens who observe our Solar system in the microwave range of the electromagnetic spectrum see a pretty bright star - the Earth. Humans have obviously increased the concentration of radio waves and microwaves emitted by the Earth by several orders of magnitude. Should we be worried about the unpredictable consequences of this unprecedented growth of the concentration of something? I don't think so. Experimentally, it seems pretty clear that the microwaves don't imply a disaster. We're not gonna ban radios, TVs, and cell phones because of some uknown hypothetical threats. Is the situation of the carbon dioxide really so different?
Or is the war against the carbon dioxide a simple manifestation of anti-civilization and anti-American emotions?