On January 1, in a post entitled Two Curious Hurricane Graphs, I observed that the mean longitude of Atlantic storm measurements had migrated east and that the entire increase in Atlantic storm-days had occurred in the east Atlantic, illustrating the point with several graphics. To my knowledge, neither fact had ever been previously published. I noted that the restriction of the increase to the east Atlantic was an indication that the increase might reflect methodological, rather than climatological factors.
Yesterday, Roger Pielke noted that Holland and Webster had posted a PPT online, parts of which can only be interpreted as a response to this criticism. Prior to my post, to my knowledge, Holland and Webster had never discussed differing trends between the east and west Atlantic. Yet within 2 weeks, they posted up a PPT contesting my suggestion that the differing trend between east and west Atlantic counts might be a technological rather than climatological trend. Although they didn’t cite climateaudit, I think that it’s fair to see that they were responding to our raising the issue.
However they fail to prove their point. Their key PPT argument on the east-west issue is that tropical storms originating in all Atlantic quadrants had increased.
Reviewing briefly, in my earlier calculation, I showed that storm-days had increased in the east Atlantic and not in the west Atlantic, dividing at the median storm measurement longitude 68W East Atlantic figure shown here; west Atlantic in original post).
Figure 1. East Atlantic storm-days. Similar figure for west Atlantic storm days does not show trend.
Holland and Webster’s PPT figure also divided the Atlantic in the same location, but instead of counting storms or storm-days in the east and west Atlantic, they counted storms originating in each of 4 quadrants (with the N-S break at about 22N). In the figure below, I’ve done a cross-tabulation in which I assigned each storm to a quadrant based on the location of its measurement exceeding 35 knots and then counted storm-days in 5 longitude quintiles. I’ve also plotted trend lines for each cell for the period 1905 to 2006 – the first year matching HW. I’ve added 2006 data. These guys are specialists – you’d think that by January 2007 they’d have collated 2006 data. Memo to HW – I’ve done it; why don’t you. Hey, you can even use my collation – I’ve archived it. The graphic is cramped, but there’s not substitute for looking at data.
First, the choice of 1905 as a start seems, shall we say, a little opportunistic when one looks at the high values in the years preceding 1905. Yeah, yeah, I’m sure that they were only concerned about data quality, just like mutual fund salesmen. But if you’re going to cherry pick start dates like this, they should disclose that the immediately preceding values were high.
Secondly, if you look at the row totals, you see that increased storm-days occur only in the east Atlantic – the result that I had previously reported (shown here in quintiles instead of halves).
Third, if you look at the column totals (which is what HW reported, as I understand it), you see that storm-days did not increase for storms regardless of originating quadrant, since there was a decline for storms originating in the SW quadrant even with the cherry-picked start date.
The only cells showing an increase are in the east Atlantic and even these trends are tainted by the cherry-picked start date.
Figure 2. Atlantic Storm-days. Columns – 4 quadrants for hurricane origin adopted visually from Holland and Webster PPT and total; rows – 5 longitude quintiles for storm (winds exceeding 35 knots). Totalled across rows and columns. Grand total is scaled 0-120; all others 0-60.
So while it may be possible that the increase is climatological rather than technological, the evidence and analysis presented by Holland and Webster is far from proving the point.