I ended up in a brief Twitter exchange yesterday with Roger Pielke Jr. He had responded to a tweet from Jeffrey D. Sachs with the following
— Roger Pielke Jr. (@RogerPielkeJr) November 12, 2013
The figure is from Elsner et al. (2008). The numbers a the top are maximum wind speeds (m s-1) and represent the values at each quantile (0.2, 0.4, 0.6, 0.8). The numbers at the bottom are for the (unseen) figure below, so ignore them. The y-axis is the trend (m s-1 yr-1). What this is telling us is the rate at which the maximum wind speed at each quantile is changing per year. This is explained quite nicely in the paper – when discussing global trends – when it says
For example, at the 80th percentile, on average 17 cyclones globally exceed 49 m s-1. With a 1oC rise in SST, the 80th percentile increases to 51 m s1. At this threshold level, on average 13 cyclones per year are observed. So the increase in SST of 1 oC results in an increase in the global frequency of strong cyclones from 13 to 17 cyclones (31%) per year.
Now, there is much more that could be said about this paper. I, however, don’t have much time to write this post and Phil Plait (the Bad Astronomer) has already covered it in quite some detail.
What I thought I would do here is pose a question for discussion. It seems that Roger Pielke Jr has interpreted the analysis for the Western North Pacific (WNP – the figure in his tweet, and the region relevant for Typhoon Haiyan) as implying that there is no trend. This is because the 90% confidence interval spans 0 m s-1 yr-1. Is he correct to interpret it in this way? Alternatively, considering only the data for the WNP, can one actually say more? For example, could one conclude that the analysis of the WNP implies that a positive trend is more likely than a negative trend (or no trend)? I know what I think, but I’d be interested in what others thought. As usual, please bear the moderation policy in mind, especially as I may be a bit too busy today to due much moderating.