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Global Warming and Plant Respiration
Volume 9, Number 36: 6 September 2006

In a "Perspective" article recently published in Science, King et al. (2006) say "it has been predicted that plant respiration, and leaf respiration in particular, will increase in a future warmer world." But, as they rhetorically ask, "are these predictions consistent with observations from modern experimental studies?"

The answer to this question is extremely important, for the five researchers note that "higher plant respiration at warmer global temperatures would release more CO2 to the atmosphere, resulting in lower net ecosystem carbon uptake, even higher atmospheric CO2 concentrations, and consequently more warming ... of as much as 2.5C by 2100," which is just what the world's climate alarmists want everyone to believe is in store for the globe if anthropogenic CO2 emissions are not dramatically reduced right now.

So ... what is the answer to King et al.'s self-directed question?

The Oak Ridge National Laboratory scientists say "many studies have shown that the increase in plant respiration in response to an increase in temperature is a short-term, largely transient response," and that "plants experimentally grown at higher temperatures often respire at nearly the same rate as plants grown at cooler temperatures." In addition, they note that "plants from warmer climates often show a much-reduced sensitivity to temperature change when compared to plants from cooler climatic regions."

How well do state-of-the-art climate models replicate these experimentally-derived observations?

King et al. report that some models "differentiate among vegetation types, such that the response to warming temperatures of tropical vegetation is smaller than that of boreal vegetation," and that in some models "respiration increases more slowly with warming at higher temperatures than at cooler temperatures." However, they report that "even these models do not include the time-dependent acclimation to a change in temperature within a few days observed in experiments."

To elucidate the significance of this shortcoming of contemporary climate models, King et al. "investigated the influence of temperature acclimation of leaf respiration on simulated carbon dynamics and climate-carbon feedbacks at both the local ecosystem scale and the global scale." In doing so, they found that about 9% more carbon is stored in plants and soil when the experimentally-observed acclimation of plants to global warming is included in coupled climate-carbon models. Furthermore, since merely eliminating the erroneous positive feedback generated by current climate models can reduce projected global warming at 2100 by as much as 2.5C, including the real-world negative feedback derived from experimental studies should reduce projected global warming even more.

This is not to say there is no place for climate models in deliberations over what to do (or not do) about anthropogenic CO2 emissions; it merely indicates that even the best of such models likely still fall short of reality in many respects, such as the one described by King et al. We have historically been far too hasty to accept at face value and with little questioning what climate models have told us at various stages of their development. We need to repent, as it were, and proceed more cautiously in the future. To "rush in," as some would have us do, and enact draconian measures designed to eliminate the lion's share of current anthropogenic CO2 emissions on the basis of climate model projections is to play the fool at best ... and something far less benign at worst.

Sherwood, Keith and Craig Idso

Reference
King, A.W., Gunderson, C.A., Post, W.M., Weston, D.J. and Wullschleger, S.D. 2006. Plant respiration in a warmer world. Science 312: 536-537.