Cosmic Radiation Makes Trees Grow Faster

Diamonddavej writes "The BBC reports that researchers at the University of Edinburgh have found that Galactic Cosmic Rays (GCRs) somehow makes trees grow faster. GCRs vary according to the 11-year solar cycle, with more GCRs hitting the Earth during solar minimum when there is a lull in the solar wind, which normally acts to protect the inner solar system from external galactic radiation. The mechanism might have something to do with GCRs increasing cloud cover, which diffuses sunlight and increases the efficiency of photosynthesis. Nevertheless, the researchers remain mystified and are requesting further ideas and research collaboration to test hypotheses. (How about Radiation Hormesis, AKA 'Vitamin-R?')" Here is the paper's abstract at the journal New Phytologist. The researchers say: "The relation of the rings to the solar cycle was much stronger than to any climatological factors. ... As for the mechanism, we are puzzled."

Comments

causality is possibly wrong

[wizardforce]

If the solar cycle is what determines the level of GCR that gets to Earth then it may very well have absolutely nothing to do with the tree growth its self but an indicator of solar conditions which influence tree growth rates.

Re:causality is possibly wrong

[khayman80]

That's what I'm thinking too. GCR intensity is highest when sunspot activity is lowest, generally modulating on an 11 year cycle. But solar irradiance also varies at the same frequency; the Sun is actually (~0.1%) brighter when more sunspots are present, contrary to intuition.

If tree growth between 1953-2006 really is highest when sunspot activity is lowest, that implies trees grow faster when the Sun is very slightly dimmer. Weird. Their diffusion explanation makes sense, but as they note this cloud condensation effect is supposed to be a very small effect. Perhaps it's just large enough to be noticed in these proxy data, though. I agree, however, that a link to solar irradiance is more intuitively appealing, and it's not immediately obvious how it could be ruled out.

I'd bet they've already considered this issue and ruled it out, possibly by using satellite measurements of solar irradiance and solar wind over the last few decades. They're supposed to be tightly correlated, but if the solar wind varies even slightly differently than solar irradiance it should be possible to see which is causing this variation in growth rates.

Cloud cover

[MichaelSmith]

The mechanism might have something to do with GCRs increasing cloud cover, which diffuses sunlight and increases the efficiency of photosynthesis.

How about cloud cover leads to more precipitation?

Re:Nitrogen Fixation

[AJWM]

Only lightning and cosmic rays can form nitrogen oxide, and lightning is relatively rare,

Well no, lighting is fairly common, actually -- there's always a lighting storm going on somewhere. However, if one assumes that the global rate of lightning is fairly constant then given that the amount nitrogen oxides contributed by cosmic rays fluctuates, you'd still see a correlation. So you may be right.

Sun spots

[Anonymous Coward]

At the university I studied physics at, they had a nice (old) telescope with which they projected solar images to count sun spots. They had a graph on the wall of the number of sun spots, going decades back. There was a nice periodicity in that graphc, and interesting thing is that they could point out two types of events: good wine years, and the occurrence of the "Elfstedentocht" (a major Dutch ice skating event which only happens when the outdoor ice conditions are exactly right).

I forgot which one happened at sunspot maxima and which at the minima, but there was a striking correlation.