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Stardate
20030709.1313 (On Screen): A group of researchers planted trees in New York City and outside of urban areas in New York, and monitored how they'd grown. They were astounded to find that the trees inside of NYC had grown twice as tall as the ones elsewhere.
The claimed reason? Pollution from the city. That sounds to me like a predetermined result. Certainly if the trees planted inside NYC had been stunted they'd have blamed it on pollution, but with this rather surprising result they did some really quick handwaving and tried to show that the city's pollution was high in the air away from the trees inside of NYC, but had settled down to ground level and affected the trees elsewhere.
It may well be that pollution is the problem, but part of science is to consider alternative explanations and to try to eliminate them, and there's an obvious alternative explanation which they may or may not have even considered. Due to the number of motor vehicles and large vertebrates living in NYC, I would expect that the ambient concentration of carbon dioxide would be higher inside of the city than out away from it. And there's no question at all that plants do very well when there's more carbon dioxide available.
Did they actually consider this? I suspect they didn't. It would be an extremely unpalatable result. It would mean that the hated greenhouse gas actually was doing good, and it would mean that the impact of human activity also had done good for Gaia, even if only a little. Can't have that; the morality play requires that human activity be uniformly evil and damaging.
Update: Mike points out another possibility: a city's microclimate is warmer, and he suggests that this may have the effect of extending the growing season.
Update: Bob writes to say that the actual study printed in Nature indicates that they actually did control for alternative explanations:
With regard to the trees, the study is actually far better than the ABCNews blurb would lead you to believe; they controlled for temperature, light, soil, CO2, water, and other factors. They also did growth chamber experiments with ozone and observed reduced growth consistent with their field trials. The higher ozone level in the "rural" areas they chose vs. NYC was measured, not hypothesized.
I guess I'm getting cynical about climate-science and environmental science; too many of those involved in them seem to have a political agenda now instead of exhibiting scientific detachment.
By the way, I knew they had directly measured higher ozone levels in the non-city locations. That wasn't at issue. My concern was that they'd fallen for post hoc fallacy by assuming that correlation implied causation.
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