I’d also like to point out that all life forms live in a series of ‘nows’, which include its local environment. The carbon dioxide, water, nitrogen and other nutrient levels that matter to trees are those where the leaves (and roots) are, not the “background’ level (or regional or global averages) and these levels for carbon dioxide and water are more variable than the background level is seasonally. Also forgotten is that all life forms modify said local environment to enhance their own survival. Do the reconstructions and/or the people who tout them take survival bias into account? Mann, et al, ignore this to their peril, I think.

Chris,

It’s kind of ironic that the Graybill stripbarked bristlecone pines were collected in response to Itso’s guess that they would be extra responsive to CO2 concentrations. But as it turns out, the stripbark growth pulses are actually primarily mechanical in cause and peter out as the tree gradually heals. But the real irony is that the CAGW people have latched onto them and use them as a supposed proof for global warming when they’re not, even though more study has justified Itso’s contention that CO2 does indeed act as a fertiliser for trees.

Most people accept that raising CO2 increases growth, but most of the quantification studies have been done on seedlings so there’s still discussion about how this can be scaled up to full-sized forests, and whether there is an ‘upper limit’ for CO2 fertilisation. Another hot topic is if/when the CO2-inspired growth increase will run into speed limits (often water-related). There’s also evidence that increasing CO2 increases trees’ water use efficiency.

This is all a very current research topic. There are a number of rather sexy forest CO2-fertilisation projects happening around the world now (FACE experiments), but it’s still early days. I would say that anyone who unequivicably says that they know all about it, certainly doesn’t.

http://www.co2science.org/subject/g/subject_g.php

Any idea how reliable the papers on CO2 related growth are that they list?

I’ve stratified my climate interpolations by season, which my help a little if the tree-growth data is precise enough. Parts of Austria show ‘seasonal warming’ trends in the linear approximations over the past 50 years, others don’t. Apparent warming in one season may be accompanied by warming in another, or it may not. I have a paper on this in the latest issue of the ‘Austrian Journal of Forest Science’, but I guess that may be hard to access for most people.

To be honest, I don’t much care about global average temperatures either. I’m interested in why trees seem to be growing faster. Perhaps my work will add something to the climate debate, but it’s not my focus. As for which side of the debate would wave my papers around as evidence and which side would denounce me as an idiot, I don’t know yet. I guess I’ll find out, when the analyses are finished.

One could of course argue that this should balance out over many years and over a wide enough sample set, but it should at least be acknowledged that that is an assumption, not something that follows from the data itself.