Proponents of carbon-dioxide emissions reductions, seeing the scientific basis for them as a means to reduce global warming collapsing in the wake of Climategate and the many other revelations of corruption of the scientific process by anthropogenic global warming alarmists, are looking for other justifications for their aims.

Many of them cheered when a Stanford scientist published a study that claimed that “Urban CO2 Domes” indirectly increase the risk of premature death for city dwellers. Science Daily reported prominently on the article. The ever-dependable wolf-crier Grist.org trumpeted the message. The Financial Times picked up the story. New Republic blogger Bradford Plumer sounded the alarm.

But what few of them stopped to do was to ask how credible the study’s findings were. Actually reading the study’s full text rather than just its summary (the journalist’s and advocate’s usual practice) might have given them pause—especially if the readers had even an elementary grasp of statistical significance. When I read it, I immediately wondered how robust its results were and suspected that there likely were problems of statistical significance involved. Sure enough, there were.

As scientists Sherwood Idso, Keith Idso, and Craig Idso—who have specialized for years in studying the effects of carbon dioxide on plant and animal life and published many peer-reviewed studies in the field—pointed out in their critique of the study, there are serious signs in the article itself that its findings are only weakly supported and, even if true, hardly of great significance.

The Idsos point out that

the many complex phenomena that are modeled by Jacobson are simply not well enough known to be quantitatively defined to the precision that is needed to derive meaningful results from the small CO2 perturbations that are associated with the urban CO2 dome phenomenon. He reports, for example, that urban CO2 dome increases in California increased the population-weighted air temperature there by only 0.0063°C, while it increased the state’s domain-averaged air temperature by a measly 0.00046°C. These increases, in turn, led to correspondingly small increases in near-surface O3 and PM2.5 concentrations, which were then input to statistical correlations that had been derived between these parameters and premature mortality.

That is, the modeled quantities are so tiny, with respect to such a large and complex system as local atmospheric, that they simply lack credibility. The study’s author, Mark Jacobsen, even admits as much in the published article. The Idsos highlight some examples:

Jacobson acknowledges that his “modeled pollution changes and their health impacts are uncertain.” In the case of ozone, for example, he specifically states that “the relationship between ozone exposure and premature mortality is uncertain.” And in the case of particulate pollution, he reports that “overall, PM2.5 increased with increasing CO2, but because of the opposing effects of temperature and water vapor on PM2.5, the net positive correlation was weak (r = 0.022) and not statistically significant (p = 0.17).”

But the problem doesn’t end there. The study’s conclusion, even if true, would hardly justify any costly effort to reduce urban carbon dioxide. As the Idsos put it:

The final result was 51 additional ozone- plus PM2.5-related premature deaths/year attributable to anthropogenic CO2 emissions, while a similar analysis for the entire United States predicted about 770 additional such deaths.

How does this country-wide number compare with the number of deaths caused by other phenomena, including various diseases and accidents? According to data in the National Vital Statistics Report of 16 September 2002, there were slightly over 2.5 million such deaths per year in the United States, which means that the premature deaths attributed to anthropogenic CO2 emissions in the analysis of Jacobson accounted for only a miniscule 0.03% of the total. And if this result justifies the imposition of economically-severe measures to reduce mankind’s CO2 emissions, what more horrendous things should be done to reduce the causes of the other 99.97% of premature deaths[,]... each one of which accounts for more fatalities than anthropogenic CO2 emissions do[?]

The study’s findings, then, lack credibility and even if true would not justify any policy response. The Idsos wisely conclude:

So why was this paper ever produced? Taking a cue from the world’s climate alarmists—who love to “follow the money trail”—we see that the primary funder of Jacobson’s study was the U.S. Environmental Protection Agency, which has recently declared CO2 to be a dangerous air pollutant, and which is desperately seeking evidence to support this illogical and unsupportable finding.