Reaching No Consensus

The New York Times wrote today of a recent study in the Proceedings of the National Academy of the Sciences [original study here] on how the Mt. Kilimanjaro ice cap has declined 26% since 2000. The author of the NYT article, Sindya N. Banhoo, goes on to say the following in the second paragraph:

Yet the authors of the study, to be published Tuesday in the Proceedings of the National Academy of Sciences, reached no consensus on whether the melting could be attributed mainly to humanity’s role in warming the global climate.

The pretty green is my contribution. Even after prettying it up, I think the language remains deceptive and fallacious. To that, then, I dedicate this post.

I don’t usually go to the source on news articles, but for some reason I felt the urge to do so in this case. One thing the NYT article doesn’t emphasize — it is mentioned later in the piece, but it isn’t the focus of the story — is in the abstract of the NAS study. To quote the authors:

The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought
4,200 years ago that lasted
300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro’s ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.

So first, it is important to note that the original NAS study is limited in scope to a discussion of the Mt. Kilimanjaro ice cap. What I think got me to look at the source was the implication by the NY Times that the authors of the study “reached no consensus” on whether the melting could be attributed to humanity’s role in global warming. It would strike me as outrageous if the authors of a narrow study on Mt. Kilimanjaro ice caps did reach such a consensus, so I had to see for myself.

Here’s what the original piece has to say on anthropogenic forcing…

The authors write:

The Quelccaya ice cap (Peru) has been monitored for more than three decades (12) and is rapidly retreating along its margins. However, the net annual mass accumulation on the summit, derived from the 2003 core and annual pit sampling, has not declined, suggesting other mechanisms are more important. Most obvious would be warmer air temperatures, which would result from the vertical amplification predicted by models that include anthropogenic forcing and are observed in the corrected vertical temperature profiles (22).

As I say often, I’m no scientist, so I don’t want to comment on the content of the article. I don’t even really want to comment on common journalistic practice. (Maybe I’ll throw this in the direction of Tom Yulsman or Keith Kloor to see what they have to say. Being exceedingly charitable to Banhoo, the information that “no consensus” was reached comes from a discussion between Banhoo and the authors of the study, not from the study itself. UPDATE: Yulsman responds, below, and then more at his own blog.) I will even confess that I easily could be wrong in interpreting the NAS article. Better to throw all those confusions in the garbage and start by supposing that the authors had written in their original report that they could “reach no consensus.”

Which brings me around to where I’d like to be. I’d like to discuss the ambiguity of implication and the appeal to ignorance.

I do agree that the question of anthropogenic global warming is a natural connection that readers might draw when learning about the content of the study. Indeed, it’s a question that the authors of the study loosely nod at in their discussion section. Is the melting ice cap a result of anthropogenic climate change? Inquiring minds want to know! So it is important for the author of the popular article — Banhoo, in this case — to address that question, and that question specifically.

But the choice of language here is unfortunate, and it is extremely difficult to parse. Nevertheless, it seems to be a common confusion among some crowds, so perhaps it needs closer treatment.

For starters, it gives the impression that the authors sought consensus, but could not reach it. Perhaps they did. We are given no information about what might have thwarted that consensus. Might it have been that there was not enough information? Might it have been that they were engaged in a tangled lover’s triangle and so couldn’t focus on the question at hand? Might it have been that several hundred mischievous kitty cats  had escaped from their cages and dumped alum, Sylvester-style, in their orange juice? There’s that problem of implication here. The researchers fought valiantly and hard. Alas, a conclusion about the effects of anthropogenic warming was not to be had.

But, second, consider the claim on its face. It’s not false. It is a true claim. The statement “The authors of the study reached no consensus on X” is true, where X equals “whether the melting could be attributed mainly to humanity’s role in warming the global climate.”

Here are a few other things that the authors of the NAS article did not reach consensus on. The scientists reached no consensus on X, where X equals:

• whether my son is being cranky with his teachers at this very moment.
• whether I liked or disliked the beer that I drank last night.
• whether it will snow in Madagascar on Tuesday.
• whether it was 45 degrees in Boulder yesterday.
• whether the severity of H1N1 can be reduced by eating a healthy breakfast.
• whether blame for the Yankees’ loss in Game 4 of the 2009 World Series should be laid squarely at the feet of AJ Burnett.

Hard to believe, but all of those statements are also true. The researchers could reach no consensus on any of those claims. Identifying points upon which the committee could not, or did not, reach consensus, is an open-ended way of approaching an enormous range of lingering questions. Indeed, I daresay that that range is infinite, even for true statements. (Don’t get me started on ‘could’.)

Third, some of the clauses X after the bullets are true, some are false, and some are arguable. Taken as a whole, however, all of the above claims are true. That’s kind of confusing, because when you say “The researchers could reach no consensus on X,” there is an implication that clause X is in doubt. Consider the layers: (a) the full claim is true, (b) the claim signals doubt, suggesting falsity of clause X, and (c) the truth or falsity of clause X is independent of whether a small group of researchers could reach consensus on it. There are three layers of confusion, so you could have a claim that is true, where the clause X is true, and nevertheless, the overall suggestion is that clause X is false. It appears from the article that the researchers have doubts either about the case for humanity’s role in warming the global climate or, more narrowly, about the case for humanity’s role in warming the global climate and melting the ice caps of Kilimanjaro. (Just as you shouldn’t get me started on ‘could’, don’t get me started on ‘consensus’.)

Which raises the fourth more important point: the implication that a given claim X is not agreed to by a select body of researchers is not evidence for or against that claim, even though it may appear to be. This is the Argumentum ad Ignorantiam fallacy, masked by the lack of consensus and the “whether” option.

So what gives? Why the mention that the researchers had reached no consensus “on whether the melting could be attributed mainly to humanity’s role in warming the global climate”? Maybe just to address the pressing question. But if so, that’s a pretty poor way of making such a point.

It seems to me that the appropriate position, therefore, is to address the question by leaving it out: either by saying that the issue of global warming was “outside the scope of the study,” or simply to emphasize what the study did reach consensus on.

UPDATE: Yulsman responds, below, and then more at his own blog.