Tree Thermometers, Did You Know That… ?
By Ed Caryl
This chart is Figure 1(b) from the Intergovernmental Panel on Climate Change Third Assessment Report, (c) 2001. The Intergovernmental Panel on Climate Change.
The source of this image is a PDF file that can be downloaded here: IPCC TAR.
Much of the data in Michael Mann’s famous “Hockey Stick” graph is derived from pine tree ring “proxies” for temperature.
- Did you know that trees do not photosynthesize at night, and during much of the winter, therefore cannot record temperature during these periods?
John Daly was first to point this out in 2000, here, along with many other points casting doubt on the Hockey Stick.
In many plants photosynthesis stops at night and at temperatures below freezing. At low light levels, temperature has little to do with plant growth. Pine trees can photosynthesize in winter, but only down to –4.5°C (Scotts Pine), due to the resin antifreeze content in their needles, but the rate of photosynthesis changes through the winter due to needle loss and day length. Pine trees also reduce their rate of photosynthesis as they age. The time constant of change in photosynthesis to a step change in temperature is 5 days.
So if “treemometers” only work during daylight, at temperatures above –4.5°C, growth varies with light level, needle loss, and age, and has a five-day temperature response time, are trees reliable enough to be used for accurate temperature reconstructions? You’d have to be one heck of a data optimist who happens to be one heck of a future climate-pessimist to believe it.