Global warming causes asthma?

A study claiming to link a climate-induced increase in ground-level ozone with asthma is breathtakingly debunked.

Researchers from the Mt. Sinai School of Medicine (Perry Sheffield) , Natural Resources Defense Council (Kim Knowlton) and the Columbia University Mailman School of Public Health (Jessie Carr and Patrick Kinney) claim in a new study published in the American Journal of Preventative Medicine that global warming will:

• Increase ground-level ozone in 14 New York City area counties from 1990 levels by an average of 3.5% by the 2020s and that
• This increase will, in turn, increase hospital emergency department visits for ozone-induced asthma attacks by an average of 7.3% in those counties by the 2020s.

Who could leave such work unabused? Not I.

First, I will not be addressing the issue of whether global warming will actually increase ground-level ozone levels. That seems to be an über-silly point given that ozone levels have declined as the much-dreaded global warming has progressed.

Next, and just for the record, in terms of mean summertime daily maximum for ozone, each of the 14 NYC-area counties was below today’s stringent EPA ozone standard of 75 parts per billion (ppb) in 1990 by between 25% to 49% (See study, Table 1). Their projected 2020 ozone values range from 20% to 45% below the current EPA ozone standard.

While I don’t see what’s the big deal with ozone in these counties, the chairman of the EPA Clean Air Scientific Advisory Council, Jonathan Samet, recently asserted that there is no safe level of exposure to ground-level ozone — even though natural levels can reach 50 ppb, higher than at least five of the levels projected for the 14 counties.

Anyway, our major concern here is with the claim that emergency room visits for asthma are connected with ozone, regardless of the ridiculously low ozone levels in question.

So, curious as to how the “researchers” connected ozone levels with emergency room visits for asthma attacks, I read the fine print and learned that the researchers assumed that every 20 ppb increase in daily maxiumum ozone causes a 4% increase in the number of emergency room visits.

The cite for this assumption is this study:

Tolbert PE, Mulholland JA, MacIntosh DL, et al. Air quality and pediatric emergency room visits for asthma in Atlanta, Georgia, USA. Am J Epidemiol 2000;151(8):798–810.

The 4%-increase-per-20-ppb-ozone assumption is derived from data summarized in the study’s Table 5, below:

Now if you look at the table entries under “8-hour ozone level (ppb)”, you’ll notice that, with the exception of the odds ratio for “≥100 vs. <50”, all the odds ratios are statistically insignificant (i.e., confidence intervals bound the no-effect level of 1.0 and the p-values all exceed 0.05).

So, in reality, the Tolbert study shows no statistical association between ozone levels up to 99 ppb and emergency room visits for asthma. Further the 99-ppb level is 65% to 138% greater than the ozone levels projected in the 14 counties for 2020.

Moving past the fact that the Tolbert study entirely debunks the new claims, Sheffield et al. would have us believe that NYC-area ozone levels cause on the order of 675 hospitalizations per year for asthma.

But who are these hospitalized asthmatics anyway? Whose asthma attack has been traced to ozone? I challenge Sheffield et al. to produce a single medical record of an asthma attack that can be linked to the ambient air of today. If there are 675 annually, surely they can produce one or maybe two? Please?

What I believe to be going on here — and, BTW, it is going on with taxpayer dollars as Sheffield et al. were funded by the EPA and National Institutes of Health — is Dungeons and Dragons® epidemiology in which inocuous data is researcher-tortured into confessing imaginary morbidity for political and pecuniary reasons.

Sheffield et al., of course, could prove my assertion wrong and shut me up by producing even one real-life victim of ambient ozone. But I doubt they will, because they can’t.