I have recently taken the time to review Chapter 6 of the UN Working Group I report (Jansen, E., J. Overpeck, K.R. Briffa, J.-C. Duplessy, F. Joos, V. Masson-Delmotte, D. Olago, B. Otto-Bliesner, W.R. Peltier, S. Rahmstorf, R. Ramesh, D. Raynaud, D. Rind, O. Solomina, R. Villalba and D. Zhang, 2007: Paleoclimate. In: 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, United Kingdom and New York, NY, USA.), which deals with an assessment of what is known about paleoclimate. I am concerned about the limitations in our understanding of the underlying physics of climate variation, as expressed in the document:
"Even though a great deal is known about glacial-interglacial variations in climate and greenhouse gases, a comprehensive
mechanistic explanation of these variations remains to be articulated. Similarly, the mechanisms of abrupt climate change
(for example, in ocean circulation and drought frequency) are not well enough understood, nor are the key climate
thresholds that, when crossed, could trigger an acceleration in sea level rise or regional climate change. Furthermore, the
ability of climate models to simulate realistic abrupt change in ocean circulation, drought frequency, flood frequency, ENSO
behavior and monsoon strength is uncertain. Neither the rates nor the processes by which ice sheets grew and disintegrated in the past are known well enough."
I am very bothered by the propensity to tweak a system that is poorly understood by scientists, let alone the politicians charged with managing the tweaks. There is a call to dedicate significant resources to manipulate current warming trends; if one does not understand the mechanisms governing the system, any tweaking is as likely to have negative effects as positive effects.
Furthermore, based on the Working Group assessment, I am not at all convinced that Global Warming per se is a bad thing. Again, from Chapter 6 of the report:
"The Mid-Pliocene (about 3.3 to 3.0 Ma) is the most recent time in Earth's history when mean global temperatures were
substantially warmer for a sustained period ... providing an accessible example of a world that is similar in many respects to what models estimate could be the Earth of the late 21st century. ... Taken together, the average of the warmest times during the middle Pliocene presents a view of the equilibrium state of a globally warmer world, in which atmospheric CO2 concentrations ... were likely higher than preindustrial values ... and in which geologic evidence and isotopes agree that sea level was at least 15 to 25 m above modern levels ... with correspondingly reduced ice sheets and lower continental aridity..."
"Lower continental aridity" seems to me to be a good thing- more water available to meet increasing human needs. Higher sea levels reduce land available for human occupation, but reduced ice cover opens significant regions of the northern hemisphere to agricultural pursuits (i.e., northern Canada, Siberia), compensating for the loss of low-lying lands, and allowing for the expansion of vegetation cover, which should help mitigate the rise in carbon concentration in the atmosphere.
Figure 6.3 of the referenced document shows the concentration of greenhouse gases with respect to the various interglacial periods over the past 650,000 years. The first thing to notice is that the normal state of the climate is glaciated- the warm periods account for only about 12% of the last 650,000 years. One also notes that the data as presented suggest much more significant rates of increase for the gases at the outset of historical warming periods than currently being experienced. I do not see the current trends representing a historically unprecedented event, nor does the historical record seem to justify the hysterical political reaction to the trend.
I do not want to create the impression that I am an advocate of continuing along the current path of human development, because I see the potential for much greater catastrophe in the near term than is posed by Global Warming. Specifically, we are facing a global water crisis and urbanization trends are posing other significant health challenges. For instance, the air we breathe is becoming more polluted as a result of significant concentrations of human endeavors in urban centers, and increasing population density poses a threat of uncontrollable spread of disease. Sanitation and the disposal of solid waste pose threats to the habitability of our environment, and it would be much more beneficial to direct scarce resources to addressing these problems. The debate should not focus on whether the climate is changing, but, rather, what investment of resources is most likely to improve the sustainability of our stewardship of Spaceship Earth.
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