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Much Ado About Tiny Temperature Trends
Volume 1, Number 1: 15 September 1998

With the publication of their paper entitled "Effects of orbital decay on satellite-derived lower-tropospheric temperature trends" in the 13 August 1998 issue of Nature (p. 661-664), Wentz and Schabel set the climate change community abuzz with their claim to have found "an artificial cooling trend in the satellite-derived temperature series caused by previously neglected orbital-decay effects." Whereas prior to their analysis of this phenomenon the satellite record that began in 1979 had shown a modest global cooling trend of about -0.05C per decade in the lower troposphere, their new calculations suggest that this portion of the planet's atmosphere has actually warmed at a rate of approximately +0.07C per decade.

One day later, in the 14 August 1998 issue of Science (p. 930-932), Hansen et al. opined that Wentz and Schabel had indeed identified the "primary reason" for the prior discrepancy between the satellite and surface temperature records that have become a core issue in the ongoing global warming debate. Nevertheless, both they and Wentz and Schabel were careful to include numerous caveats appropriate to the complexity of the problem, suggesting as well that the last word on the subject has probably yet to be heard. The next day, in fact, proved them correct, as the 15 August 1998 issue of The Economist contained an article (p. 77-79) in which satellite guru John Christy was reported to have come out with his own orbital decay correction that swung the post-1979 temperature trend of the lower troposphere back to a tiny -0.01C per decade cooling.

So where does this rapidly changing state of affairs leave us? We have no problem with any of the recently reported analyses, as all are attempting to get to the truth of the matter as best they can. And sooner or later someone will get it right. But what will we have when we get the final answer?

Hansen et al. state that the satellite data "have been the principal refuge for those who deny the reality of global warming." We agree that this is so, but contend that it ought not to have been; for it obfuscates the central issue of the climate change debate, which is whether or not the rising CO2 content of the atmosphere is the cause of global warming. By arguing primarily over whether or not temperatures are currently rising conveniently reduces the burden of proof required by those who would take action now to reduce CO2 emissions.

Consider, for example, Hansen et al.'s concluding statement: "the issue should no longer be whether global warming is occurring, but what is the rate of warming, what is its practical significance, and what should be done about it." The "what should be done about it" has everything to do with reducing CO2 emissions; and Hansen et al. could get to that point without ever having to prove that the warming, if it exists, is even related to CO2.

By itself, knowledge of whether the planet is warming or cooling is of little help to us in understanding why it is doing what it is doing. The temperature rise that gave us the Medieval Warm Period, for example, was much like the warming of the past century. But was the warmth of that prior period due to elevated levels of atmospheric CO2? Not very likely. The air's CO2 content over that period was fairly constant and much lower than it is today. Clearly, atmospheric CO2 levels had absolutely nothing to do with the development of the Medieval Warm Period or its demise; so there is no compelling reason to believe that they have anything to do with what may be happening climate-wise today.

If we are honest with ourselves and truly concerned about the earth and its biota, pursuit of the straw man of global warming must be replaced by a diligent search for the truth about CO2 and its many real and varied biospheric impacts. The world deserves nothing less.

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President
15 September 1998