Friday, 4 December 2009

A Thought That has Been Bothering Me

Ever since Colby Cosh wrote this piece, one line stuck out at me:

(“Some large-scale human influence” on “wood densities”? Oh, hell, what about the fairy hypothesis? Couldn’t woodland sprites have sprinkled magic dust on those trees?)

The tone of this reflects the "we humans are too puny to affect mass changes in the environment" line that AGW Denialists trot out regularly.

So I got to thinking, what was going on in or around the 60s that could cause trees to grow "abnormally"? (abnormal being a sudden unexplained shift that doesn't meet previous observations.)

And the premise hit me, what about atmospheric nuclear testing?

Today (thanks to commenter Dan Fisher) I read this post at New Scientist. It lays out in more detail why the tree-ring data was discarded:

Is this an unjustified "fix"? No, because some sets of tree-ring data can be compared with the direct records of local temperature for the past century. Up until the 1960s, there is a very close correlation between the density of growth rings in trees in northern latitudes and summer temperatures, but after this it starts to break down.

We don't know why. It might be that the correlation breaks down whenever it gets too hot, in which case reconstructions of past temperature that rely heavily on tree-ring data will give a misleading picture. Or it might be due to some factor unique to the 20th century, such as changes in the timing of the snow melt, in which case it will not affect reconstructions.

Well that started the whole train of thought running again. So I tried searching to see if anyone has written on the nuclear testing affecting tree-ring density angle.

Nothing yet. But I did find this:

The above-ground nuclear tests that occurred in several countries between 1955 and 1963 dramatically increased the amount of carbon-14 in the atmosphere and subsequently in the biosphere; after the tests ended the atmospheric concentration of the isotope began to decrease.

Now this is not conclusive proof that trees responded to the increase in Carbon-14. However, it is conclusive proof that human activity can have global affects, to the point that we can accurately determine a persons age by the amount of Carbon-14 in their tooth enamel.

Maybe there is enough of a correlation there to investigate if it is in fact causal. After all we banned above ground nuclear testing for a reason.

No comments: