Making a case vs. analyzing data in the climate change debate

Nate Silver recently re-launched a greatly expanded version of his fivethirtyeight blog to much fanfare. The site’s goal is to tackle a variety of questions with hard data analysis in an effort to elucidate truths that are often obscured by opinion journalism.

In its first week, fivethirtyeight published a piece from Rodger Pielke Jr. (an environmental studies professor who focuses on climate impacts) in which it was argued that climate change is not causing increased economic losses. The essential argument was that disaster losses are increasing if you look at the raw data but the upward trend disappears if you correct for the fact that GDP is also increasing. In other words, total disaster losses have increased because we are getting richer not because climate related disasters have increased (this is based on Pielke’s own research).

This was a conclusion that stirred up quite a bit of controversy and Nate Silver stated in an interview on the Daily Show that because of the reaction (much of it negative) fivethrityeight would post a rebuttal to Pielke’s article. The rebuttal was written by professor of engineering and climate change blogger John Abraham. Apparently, however, fivethirtyeight changed its mind when they received the rebuttal so Abraham instead published it at the Huffington Post.

I think Abraham’s rebuttal is disappointing because it amounts to ‘making a case’ rather than analyzing data. The goal of fivethirtyeight, and science in general, should be to dig deep into the data, question methods and assumptions and attempt to get at the truth in a complicated word. Pielke’s original claim (that economic disaster losses are increasing because of increased wealth rather than increased disasters) seems well framed to be debated in the context of math and data analysis. I think it would be very interesting to have this debate. Abraham’s rebuttal, however, does not even attempt to do this as it does no data analysis at all and does not directly refute the original claim made by Pielke.  Instead it takes the form of a ‘persuasive essay’ in which Abraham aggregates as many studies as he can that support the general narrative that climate change is increasing disasters.

This is the strategy of political pundits and ideologues, and as scientists we should resist the temptation to use it. The problem with this strategy is that creating a well-cited narrative in support of your scientific view can be easy to do no matter what your view is. Take the following example:

Lets say that you want to paint the picture that global warming is drastically increasing hurricane activity:

Hurricanes derive their power from warm sea surface temperatures (Emanuel at al., 2005) and the oceans have been warming because of human greenhouse gas emissions (Abraham et al., 2013). Accordingly, there has been a dramatic upswing in hurricanes at the end of the 20th century (Holland and Webster, 2007). Hurricane tracks will continue to move northward (Graff and LaCasce, 2014) which makes events like Superstorm Sandy more likely. Basic physics predicts that as we continue to increase greenhouse gasses, hurricanes will get stronger (Emanuel, 1987) and climate models confirm this (Knutson and Tuleya, 2004). Additionally, hurricane damage will only be exacerbated by sea level rise (Woodruff et al., 2013).

On the other hand, let’s say that you want to paint the picture that global warming’s impact on hurricane activity is small or negative:

There has been no detectable trend in hurricane frequency over the twentieth century when you account for increased observational capabilities through time (Landsea, 2007). There is no straightforward connection between hurricane strength and sea surface temperatures (Swanson, 2008) and when we look at past records, hurricanes vary much more coherently with natural climate oscillations than with increasing greenhouse gasses (Chylek and Lesins, 2008).  Climate models predict that in the future, increased wind shear (Vecchi and Soden, 2007) will reduce hurricane frequency (Knutson et al., 2008). Finally, Superstorm Sandy had a trajectory that will become less likely under global warming (Barnes at al., 2013).

Notice how both of the paragraphs are cited with peer reviewed research and thus each may seem very authoritative on their own. The problem with this type of writing (and thinking) is that it sacrifices actual data analysis in favor of making the ‘most convincing case possible’. If we want to get closer to the truth we have to abandon this style of thinking in favor of carful analysis. We have to dig into the numbers, question the assumptions and understand why there are conflicting results in the literature in the first place.

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