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Rising CO2 Concentrations Help Plants Adapt to Rising Temperatures
Reference
Cowling, S.A. and Sykes, M.T. 1999. Physiological significance of low atmospheric CO2 for plant-climate interactions. Quaternary Research 52: 237-242.

Background
In a painfully monotonous lament, we keep hearing the worn-out claim that the long awaited CO2-induced global warming - when it comes (if it ever does) - will be so fast and furious that much of earth's plant life will be forced to migrate towards cooler climates, i.e., poleward and upward, and that many species will not be able to migrate fast enough to avoid extinction. This prediction sounds logical enough - logical enough to probably convince a goodly portion of the public and their elected representatives that it's true. But, as with most IPCC scenarios, it's false.

What was done
The authors conducted a review of the literature relative to the interactive effects of concurrent increases in atmospheric CO2 and air temperature on plant growth and development.

What was learned
It was concluded that "increases in CO2 from 350 to 650 ppm are estimated to result in an up to 5C rise in Topt [plant optimal growth temperature] primarily because of a reduction in rate of photorespiration at high temperatures." The authors also noted that "experiments with P. vulgaris exposed to low CO2 indicate that Topt can decrease by approximately 4-5C with a reduction in CO2 from 380 to 200 ppm (Cowling and Sage, 1998)."

What it means
If the earth were to warm, for whatever reason, the best thing that could possibly happen to the environment would be for the air's CO2 concentration to rise concurrently, or shortly thereafter; for there would then be no need for the vegetation of the planet to have to migrate to cooler climates. As the air temperature rose higher and higher, for example, so also would the temperature at which nearly all plants function at their optimum rise higher and higher; and they would continue to grow and reproduce just fine right where they were when the air temperature rise began.

Interestingly, it would appear that this is exactly how nature operates following a glacial termination. In response to the air temperature increase experienced in going from a glacial age to an interglacial period, earth's atmospheric CO2 concentration has typically risen by an amount sufficient to allow earth's plants to adequately cope with the climate change, as Cowling and Sage's work indicates that a typical 180 ppm increase in atmospheric CO2 concentration from a base level characteristic of full glacial conditions can raise plant optimum growth temperature by 4-5C, which is the degree of temperature increase typically experienced in most glacial terminations. Hence, rather than a model-inspired increase in atmospheric CO2 triggering a catastrophic climate change, real-world data suggest that catastrophic climate changes typically trigger life-saving changes in atmospheric CO2!

Reference
Cowling, S.A. and Sage, R.F. 1998. Interactive effects of low atmospheric CO2 and elevated temperature on growth, photosynthesis, and respiration in Phaseolus vulgaris. Plant, Cell and Environment 21: 427-435.


Reviewed 2 August 2000