Tree Ring Circus™

For those of you laymen following the CRU document dump I'd like to make a few points about one of the central issues: Using tree ring width as a thermometer in order to have a record of temperature from the era before thermometers were invented. Tree rings were the genesis of the famous hockey stick "proving" that temperatures had been flat for a thousand years or more and suddenly with CO2 rising Earth's temperature system was rising out of control. Doom was coming if things continued this way and electricity production and automobiles powered by carbon and hydrocarbon fuels were the cause of the coming catastrophe.

But the boys reading the rings found something interesting. The ring "temperature" in the modern era was going down while the "real" temperature was going up. This is called the "great divergence" (really it is just called "divergence" but I like my phrase better). So what did they do to make the rings agree with the measured temperatures? They grafted on "real" temperatures. This is not exactly kosher if you don't know what caused the great divergence.

What the divergence tells us is that tree rings are not a good way to measure temperature because we lack all the relevant confounding variables. Like rainfall. Air quality (volcanic eruption?). CO2 content of the atmosphere. Nearby forest fires. Cloud cover. etc.

To say something caused the divergence is true. But if you discard the later data you also have to discard the prior data until you know the cause.

And it is dishonest in the extreme to append “real” values on a chart of calculated values without making that explicit each an every time the chart is presented and the data used. Especially in a public policy context. Like the hockey stick.

The idea of deriving temperatures to an accuracy of .1 deg C or even .5 deg C from tree rings is a triumph of self delusion over error bars.

If you want to dig into this some good search terms are: dendrochronology, Yamal, hockey stick, tree ring, Real Climate, Watts, McIntyre, Climate Audit, temperature.

Her is a link rich site. A search for "Watts" on the page will get you started on a deeper look.