Category:Biological effects of carbon dioxide enrichment

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The Contribution of Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) hardly mentions the beneficial effects of earth’s rising atmospheric carbon dioxide (CO2) concentration on the biosphere. In a chapter titled “Changes in Atmospheric Constituents and in Radiative Forcing” the authors say the following (IPCC, 2007–I, p. 186):

Increased CO2 concentrations can also “fertilize” plants by stimulating photosynthesis, which models suggest has contributed to increased vegetation cover and leaf area over the 20th century (Cramer et al., 2001). Increases in the Normalized Difference Vegetation Index, a remote sensing product indicative of leaf area, biomass and potential photosynthesis, have been observed (Zhou et al., 2001), although other causes including climate change itself are also likely to have contributed. Increased vegetative cover and leaf area would decrease surface albedo, which would act to oppose the increase in albedo due to deforestation. The RF due to this process has not been evaluated and there is a very low scientific understanding of these effects.

Later in that report, in a chapter titled “Couplings Between Changes in the Climate System and Biogeochemistry,” a single paragraph is devoted to the “effects of elevated carbon dioxide” on plants. The paragraph concludes, “it is not yet clear how strong the CO2 fertilization effect actually is” (p. 527).

Since CO2 fertilization could affect crop yields and how efficiently plants use mineral nutritients and water, one would expect the subject to be addressed in the Contribution of Group 2, on “Impacts, Adaption and Vulnerability,” and indeed it is, in a chapter titled “Food, Fibre and Forest Products” (IPCC, 2007-II). But that chapter belittles and largely ignores research on the benefits of enhanced CO2 while exaggerating the possible negative effects of rapidly rising temperatures and extreme weather events predicted by computer models. The subject is not even mentioned in Chapter 8 of that report, on “Human Health,” although even a modest effect on crops would have some effect on human health. (See Chapter 9 of the present report for our own, more complete, discussion of the health effects of climate change.)

The IPCC’s failure to report the beneficial effects of rising CO2 concentrations is surprising when literally thousands of peer-reviewed journal articles exist on the subject. It is also a major defect of the IPCC report and one reason why it is not a reliable summary of the science of climate change. In this chapter, we seek to provide the balance that eluded the IPCC.

The chapter begins with a survey of the scientific literature on the productivity responses of plants to higher CO2 concentrations, and then reviews research on the effect of enhanced CO2 on plant water-use efficiency, responsiveness to environmental stress, acclimation, competition among species (e.g., crops versus weeds), respiration, and other effects. We end with a survey of literature showing the general “greening of the Earth” that has occurred during the Current Warm Period.


The following pages are taken from Climate Change Reconsidered and can be used as a guide to get you through the basics of this category:

Acclimation

Amelioration of Environmental Stresses

Carbon Sequestration

Competition

Greening of the Earth

Other benefits

Plant productivity responses

Respiration

Water use efficiency


References

Cramer, W., A. Bondeau, F. I. Woodward, I. C. Prentice, R. A. Betts, V. Brovkin, P. M. Cox, V. Fisher, J. Foley, A. D. Friend, C. Kucharik, M. R. Lomas, N. Ramankutty, S. Sitch, B. Smith, A. White, and C. Young-Molling. 2001. Global response of terrestrial ecosystem structure and function to CO2 and climate change: Results from six dynamic global vegetation models. Global Change Biol. 7: 357-373.

IPCC. 2007-I. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller. (Eds.) Cambridge University Press, Cambridge, UK.

IPCC. 2007-II. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and Hanson, C.D. (Eds.) Cambridge University Press, Cambridge, UK.

Zhou, L.M., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V., and Myneni, R.B. 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999. Journal of Geophysical Research 106 (D17): 20069-20083.

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