In its treatment of the general characteristics of this topic in its first six "bullet points," Information Sheet 2 is adequate; but its last six points leave much to be desired.
Point 7, for example, matter-of-factly states that adjustments to rising concentrations of greenhouse gases "will include a 'global warming' of the earth's surface and lower atmosphere." This statement is too strong. "May include" would have been appropriate, but not "will include." The explanatory text that accompanies this statement acknowledges that temperature-induced negative feedbacks may counter the primary tendency for warming; but the unstated assumption is that they cannot totally overpower it. We agree. However, there is a non-feedback phenomenon that could well accomplish this feat, especially when aided by some of the many warming-induced negative feedbacks.
The phenomenon of which we speak is the impetus for cooling that is set in motion by the direct effect of the rising CO2 content of the air on earth's vegetation. By enhancing plant productivity - at sea (Raven, 1991, 1993; Riebesell et al., 1993) and on land (Kimball, 1983; Idso and Idso, 1994; Saxe et al., 1998) - via its aerial fertilization effect, atmospheric CO2 enrichment stimulates the evolution of greater quantities of a number of biologically-produced gases (Schnell and Vali, 1976; Vali et al., 1976; Adams et al., 1981; MacTaggart et al., 1987; Staubes et al., 1989), which may ultimately lead to the production of more cloud condensation nuclei (Bigg, 1990; Novakov and Penner, 1993) that can stimulate the creation of more and brighter clouds (Saxena et al., 1995; Baker, 1997) that reflect more incoming solar radiation back to space (Idso, 1990, 1992). And this phenomenon, which can cool the planet independently of any change in the strength of the atmosphere's greenhouse effect, has been estimated to be of virtually the same strength as the typically-predicted global warming impetus of a doubling of the air's CO2 content (Lovelock, 1988; Turner et al., 1996).
Point 8 states that sulfate aerosols only remain in the atmosphere for a relatively short time, implying that they should not be relied upon "to keep the climate cool indefinitely." Again, this conclusion suffers from the non-consideration of biogenic gas emissions, the magnitudes of which will always be linked to the CO2 content of the air.
Point 9 puts the expected rise in mean global air temperature by the year 2100 at 1 to 3.5°C. However, might it not be argued that the upper bound could be one degree higher, in view of the "many uncertainties" that surround this issue? And, if so, might it not also be argued that the lower bound could be one degree lower? Clearly, one cannot have extreme confidence in the stated bounds; and but a further 1°C extension of the lower bound would admit the possibility of no temperature change at all.
Point 10 states that "past emissions have already committed us to some climate change." In view of our comments relative to the proceeding three points, we would feel more comfortable saying past emissions may have done so. We cannot currently be confident they have already so acted.
Point 11 states that "there is evidence that climate change has already begun." Indeed, climate change is the norm, as the earth is imbedded in all sorts of climatic cycles that operate over a vast array of time scales. But, is the past century's rise in atmospheric CO2 the cause of the past century's warming?
The apparent correlation between CO2 and temperature over the recent historical record is often presented as "evidence" that future increases in CO2 will result in catastrophic global warming. However, as we pointed out in our Volume 2 Number 7 Editorial CO2 and Temperature: The Great Geophysical Waltz and in our Volume 2 Number 8 Climatological Review CO2 and Temperature: Ice Core Correlations, CO2-temperature trends over a much longer period of time (250,000 years) indicate that, contrary to current climate model implications, this simplistic notion has little real-world data to support it. Following the penultimate deglaciation, for example, atmospheric CO2 concentrations exhibited no net change for approximately 15,000 years, during which period air temperatures dropped all the way back to values characteristic of glacial times (Fischer et al., 1999). Then, when CO2 finally began to decline, air temperatures remained constant for a few thousand years, after which they actually rose for about 6,000 years. And even when the two parameters increased in unison, as they did during the three most recent glacial terminations, temperature always rose first, followed by CO2 concentrations some 400 to 1,000 years later.
Clearly, the concomitant increase in atmospheric CO2 and air temperature over the last century or so proves nothing of a cause-and-effect nature. When all available CO2 and temperature records are analyzed, one can find much longer periods of absolutely no correlation and even opposing trends.
Point 12 states that "it is too early to predict the size and timing of climate change in specific regions." In light of the materials discussed above, we feel it is also too early to make such predictions for the world as a whole.
References
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