Wednesday, July 16, 2008

Stupid Human Assumption

Early this week, I experienced another "poke the monkey" episode (see the comment section). This time, my loyal commenter, Josh, sent me a Proceedings of the National Academy of Sciences (PNAS) article that links global warming with increased incidence of kidney stones (here is press coverage that attempts to explain the journal article). In a previous post (Wanted: Fact Checker), I talked about the seeming lack of rigor in the peer review process at PNAS. I don't think peer review was the problem in this case, but the article does have some serious issues.

The first serious issue that I have with the journal article is well covered at Steve McIntyre's Climate Audit website. Here is the kernal of importance from Steve's site:

  • "... it turns out that the current kidney stone dataset is not so good for a variety of reasons. These include undiagnosed, asymptomatic stones, lack of correct documentation of recurring events, or those who just plain don’t go to the hospital. In fact, there could be up to a 35% error in the baseline prevalence of kidney stone disease! See, reconstructing climate records is nothing compared to ascertaining a census of those suffering of kidney stones."
Apparently, we really don't know how many people suffer from kidney stones very well. Since we don't this number now, how will we be able to determine whether a future increase in kidney stone incidence is due to medical science improvements in kidney stone diagnosis or to increased temperature caused by global warming.

The other real issue I have with this sort of study is that it makes the classic assumption of "stupid humans". I don't follow kidney stone medical literature, but from what I can gather, a mean annual temperature above a certain degree (I think it is 13 degrees C) is correlated with increased risk of kidney stones. Basically, where it's hot, there is higher percentage of the population that is diagnosed with kidney stones.

The authors of the study assumed the worst case among the climate scenarios published by the IPCC (SRESa1b) and placed the GCM modeled temperature increases on top of today's instrumented temperature record to get mean temperatures in the future. I have no problem with this except for my well-known objections to GCMs that I will lay aside for now. What we end up with is a greatly expanded "Kidney Stone Belt" in the southern and southwestern U.S.

Where does the "stupid human assumption" come into play? In the press account, we find out the best way to prevent kidney stones is to simply drink more water. The authors implicitly assume that humans will not change their behavior in response to climate shifts. Does that make sense to you? I know if I started hearing about 30% rises in kidney stones among my neighbors, I would start drinking more water. Actually, the response of an individual to this sort of increased risk is "so easy even a caveman could do it."

Finally, an interesting tidbit that came out on Climate Audit: "The SE United States has actually undergone slight cooling over the past century." Isn't that a kick in the pants to the authors? It is cooling in the present Kidney Stone Belt.

Now, if there were just someway to tell me if the authors of this study are looking for more funding of kidney stone research... Ahhh, there it is. "The related cost of the predicted increase in kidney stones would be $900 million to $1.3 billion as the kidney stone belt expands northward and westward from warming, the researchers said."

As my buddy Chip would say, "What ARE the odds!?!"

1 comment:

Josh & Margo said...

I feel honored to have my name mentioned.

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