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Effects of a Warming, Drying and CO2-Accreting Atmosphere on European Forest Productivity
Reference
Davi, H., Dufrene, E., Francois, C., Le Maire, G., Loustau, D., Bosc, A., Rambal, S., Granier, A. and Moors, E. 2006. Sensitivity of water and carbon fluxes to climate changes from 1960-2100 in European forest ecosystems. Agricultural and Forest Meteorology 141: 35-56.

Background
The authors report that "predictions for the second half of the 21st century diverge, with some models predicting that the terrestrial carbon sink will tend to level off, while others predict a decrease [our italics]," noting, in this regard, that "forest ecosystems play a dominant role in controlling terrestrial carbon sinks."

What was done
Hoping to shed more light on this important subject, Davi et al. used a meteorological model following "a moderate CO2 emission scenario" - B2 of the IPCC - to calculate a 1960-2100 average temperature increase of 3.1C and a mean summer rainfall decrease of 27%, which they used as input to a physiologically-based multi-layer process-based ecosystem productivity model (which contained a carbon allocation sub-model coupled with a soil model) to evaluate net productivity changes of six French forest ecosystems representative of oceanic, continental and Mediterranean climates that are dominated, respectively, by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) and sclerophyllous evergreen species (Quercus ilex), which ecosystems, in their words, "are representative of a significant proportion of forests in western Europe."

What was learned
"By comparing runs with and without CO2 effects," according to the researchers, they found that "CO2 fertilization is responsible from 1960 to 2100 for an NEP [net ecosystem productivity] enhancement of about 427 g(C) on average for all sites (= 3.05 g(C) m-2 year-1)," noting that "the CO2 fertilization effect" actually turns a warming- and drying-induced "decrease of NEP into an increase." In addition, they report that "no saturation of this effect on NEP is found because the differences between the simulations with and without CO2 fertilization continuously increase with time."

What it means
Even in the face of what truly would be an "unprecedented" global warming and drying scenario, the real-world physiological effects of atmospheric CO2 enrichment that are included in the ecosystem productivity model employed by Davi et al. are able to more than compensate for the deleterious effects of the dramatic climate-change scenario on the productivity of major European forests.

Reviewed 28 February 2007