Just a teaser: The 1947 Mackenzie River delta ends with this sentence: “Whaterver the cause, we can look to these northernmost American trees for proof of borderline stability for at least five centuries”

It is too bad their chronologies did not extend back further – eyeballing the graph seems seem to get interesting in the 1400s, not to mention at the right-hand side of the graph in the ’30s.

#54, Dave, thanks for your comments. I suspect that seasonal climatic variations ought to factor out in a kinetic rate ratio, because both carbon isotopes of CO2 would be influenced identically, leaving nothing but a temperature signal. I don’t have time just now to look into the idea and it’s been a very long time since I did any physical organic chemistry, but maybe it would eventually be worth checking out. It certainly has the promise of producing results faster than generation-long greenhouse growth parameterization studies.

I guess I can give it a rest, since I⢢¯ve made the point.

That would be great, because you’ve made the point maybe 100 times.

I’m sure that Steve has publications in the pipeline, and it would be improper for him to presage them on the blog.

That said, there has been an explosion of quality thinking on CA in the last couple of months – I don’t know if that’s due to the profile of the NAS panel or the vindication in the Wegman report (or neither) but it’s very entertaining and worthwhile.

One problem I see is that most of the isotope separation would come at the step where CO2 from the air is captured. I’m not sure of the exact details, but I know that grasses tend to capture energy from the sun during the day and then used the captured energy to capture CO2 at night when it’s cooler and they can open their stomata to let more air in without losing too much water in the process. That’s one big aspect of the CO2 fertilization effect, for instance; it lets non-grassy plants keep their stomata more closed thus saving water loss.

But that brings up one thing to be considered with trees. Since they aren’t grasses, they must open their stomata while they’re photosynthesing, and this means that to be effective they must be able to afford to lose the water which escapes while they’re capturing CO2. So it’s precisely when it’s warmest, and thus they’re most able to produce sugars for growth that they’re most likely to be vulnerable to water stress. If it’s either not THAT warm so not too much water is being lost or they have ample water availability they will grow lots, but if its really hot and they don’t have enough water then the opportunity is lost which would show up as smaller rings than there might have been.

But as far as the isotope composition of what growth there was, that might be tricky. If you had dry ground but a wet spring and lots of growth in early summer then less growth during the hotter weather then it’d look isotopically like it was a cooler year than if you had lots of carryover moisture in the soil and this allowed plenty of growth in the hottest part of the summer even though the actual average temperature was higher. I suppose if you could actually measure isotope composition from various parts of the year this would help untangle things but it sounds tricky.