2010-11-17 13:54:52Help finding peer-review references on 'CO2 is plant food'
John Cook


I don't suppose anyone can help me track down one or two peer-reviewed papers that back up this statement in the Guide:

  • The “CO2 fertilizer” effect is limited and is quickly overwhelmed by the negative effects of heat stress and drought.
2010-11-18 02:26:34
Ari Jokimäki


If you're not in hurry, I might start working on a new paperlist tomorrow... ;)

Edited to add: ...or it might be today for you already.

2010-11-18 18:32:34
Ari Jokimäki


Here's one possible reference:


"The effect that rising atmospheric CO2 levels will have on forest productivity and water use efficiency remains uncertain, yet it has critical implications for future rates of carbon sequestration and forest distributions. Efforts to understand the effect that rising CO2 will have on forests are largely based on growth chamber studies of seedlings, and the relatively small number of FACE sites. Inferences from these studies are limited by their generally short durations, artificial growing conditions, unnatural step-increases in CO2 concentrations, and poor replication. Here we analyze the global record of annual radial tree growth, derived from the International Tree ring Data Bank (ITRDB), for evidence of increasing growth rates that cannot be explained by climatic change alone, and for evidence of decreasing sensitivity to drought. We find that approximately 20 percent of sites globally exhibit increasing trends in growth that cannot be attributed to climatic causes, nitrogen deposition, elevation, or latitude, which we attribute to a direct CO2 fertilization effect. No differences were found between species in their likelihood to exhibit growth increases attributable to CO2 fertilization, although Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa), the two most commonly sampled species in the ITRDB, exhibit a CO2 fertilization signal at frequencies very near their upper and lower confidence limits respectively. Overall these results suggest that CO2 fertilization of forests will not counteract emissions or slow warming in any substantial fashion, but do suggest that future forest dynamics may differ from those seen today depending on site conditions and individual species' responses to elevated CO2."

2010-11-18 18:42:50
Ari Jokimäki




"Here, we provide new evidence from a FACE experiment in a deciduous Liquidambar styraciflua (sweetgum) forest stand in Tennessee, USA, that N limitation has significantly reduced the stimulation of NPP by elevated atmospheric CO2 concentration (eCO2). Isotopic evidence and N budget analysis support the premise that N availability in this forest ecosystem has been declining over time, and declining faster in eCO2. Model analyses and evidence from leaf- and stand-level observations provide mechanistic evidence that declining N availability constrained the tree response to eCO2. These results provide a strong rationale and process understanding for incorporating N limitation and N feedback effects in ecosystem and global models used in climate change assessments."

2010-11-18 20:28:38
Rob Painting


Zhao & Running 2010

Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009

"Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by plants and accumulated as biomass. Previous studies have shown that climate constraints were relaxing with increasing temperature and solar radiation, allowing an upward trend in NPP from 1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental measurements began, which could imply continued increases in NPP; however, our estimates suggest a reduction in the global NPP of 0.55 petagrams of carbon. Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel production"

So much for the CO2 fertilization effect, drought is already getting the upper hand.

2010-11-18 21:59:05
Ari Jokimäki


Here are some more:


2010-11-20 06:06:53More again, from Julian...
John Cook

Crop failure:
(PDF here: http://iopscience.iop.org/1748-9326/5/3/034012/pdf/1748-9326_5_3_034012.pdf)


Impacts of higher temperature:

General background:

http://www.pnas.org/content/104/50/19686.full (meta-type study)

Water stress:

Mitchell, R.A.C, V.J. Mitchell, and D.W. Lowler, 2001:  Response of wheat canopy and water gas-exchange to soil water content under ambient and elevated CO2.  Global Change Biology, 7, 599-611.

Schurr U., T. Gollan, and E.D. Schulze, 1992:  Stomatal response to drying soil in relation to changes in sap composition of Helianthus annuus. II. Stomatal sensitivity to abscisic acid imported from the xylem sap.  Plant Cell Environ., 15, 561–567.


"English" version of above here: http://www.sciencedaily.com/releases/2010/03/100330102833.htm

Nutrient limitation in forests:
2010-11-20 06:52:44
Ari Jokimäki

It constantly amazes me how much research there is for each subject. You know, back when I used to be an active online debater on climate science, the deniers used to claim that we haven't studied this or that and every time you looked the papers on this and that you would find dozens of papers.
2010-11-20 06:59:06No evidence
John Cook


That's why whenever a denier says "there's no evidence", I say they haven't looked hard enough.

Of course, we're trying to hand them the evidence on a silver platter nowadays so they have no excuse.