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Three Decades of Modeling Climate Sensitivity to CO2
Volume 11, Number 33: 13 August 2008

We still can't predict future climate responses at low and high latitudes, which constrains our ability to forecast changes in atmospheric dynamics and regional climate. Thus states the subtitle of the Bernard Haurwitz Memorial Lecture presented by NASA Senior Scientist David Rind of the Goddard Institute for Space Studies at the 16th Conference on Atmospheric and Oceanic Fluid Dynamics, which was held on 25-29 June 2007 in Santa Fe, New Mexico (USA) and published in the June 2008 issue of the Bulletin of the American Meteorological Society (Rind, 2008).

Rind begins his review and analysis of this important subject by noting that Charney et al. (1979) concluded that global temperature sensitivity to a doubling of the atmosphere's CO2 concentration was "between 1.5 and 4.5C," while noting that since that time "we have not moved very far from that range." In addition, he reports that uncertainty in our assessment of high- and low-latitude climate sensitivity "is also still as great as ever, with a factor of 2 at both high and low latitudes."

As to why this is so, Rind lists a number of separate problems. For one thing, whether the water vapor response to warming employed by climate models "is realistic is hard to assess," as he puts it, "because we have not had recent climate changes of the magnitude forecast for the rest of this century" to test it against. Closely associated are low-latitude difficulties related to modeling both low- and high-level clouds in the tropics and the physics and dynamics associated with them, plus high-latitude difficulties associated with cryosphere feedbacks related to sea ice and snow cover.

One approach to dealing with these uncertainties has been to suggest, in Rind's words, that "we can have greater confidence in the multi-model mean changes than in that of any individual model for climate change assessments." However, he says "it is doubtful that averaging different formulations together will end up giving the 'right' result," since "model responses (e.g., tropical land precipitation) can often be of different signs, and there can be little confidence that averaging them together will produce a better result."

Rind thus concludes that "at this point, we cannot determine the low- and high-latitude sensitivities, and we have no real way of obtaining them [our italics]," which unknowns, in his opinion, "affect the confidence we can have in many of our projections of atmospheric dynamic and hydrologic responses to global warming."

Because of these and a host of other complexities he discusses, Rind states that "forecasting even the large-scale response to climate change is not easy given the current uncertainties," and that "regional responses may be the end result of varying influences in part due to warming in different tropical and high-latitude regions." Hence, it would seem to us there is little reason to put much confidence in the types of local projections climate alarmists typically use to promote fears about what those projections portend.

As to what Rind's analysis of the climate modeling enterprise suggests about the future, he writes that "real progress will be the result of continued and newer observations along with modeling improvements based on these observations," which is a conclusion we can readily endorse, as it clearly and rightly indicates that modeling improvements should be based on "continued and new observations," which must provide the basis for evaluating all model implications. So difficult will this task be, however, that he says "there is no guarantee that these issues will be resolved before a substantial global warming impact is upon us." However, because of the large uncertainties -- and unknowns -- surrounding many aspects of earth's complex climatic system, there is also no guarantee there even will be any "substantial global warming impact" due to a doubling, or more, of the air's CO2 content. And this fact suggests to us that the massive world-economy-altering measures that are being promoted by Al Gore and James Hansen to "solve" a "climate crisis" that may not even exist are preposterously premature and, therefore, ill-advised at best and actually dangerous in the extreme.

Sherwood, Keith and Craig Idso

References
Charney, J.G. et al. 1979. Carbon Dioxide and Climate: A Scientific Assessment. National Academy of Sciences. Washington, DC (USA).

Rind, D. 2008. The consequences of not knowing low- and high-latitude climate sensitivity. Bulletin of the American Meteorological Society 89: 855-864.