With the Atlantic Hurricane season officially starting today I think it’s past time I updated my previous post on Intense Tropical cyclone trends. Southern Hemisphere data can also be included through the end of the 2009-2010 season which I have decided to comment on because, even though I have doubts about the quality of that data, it appears that it now matters less than previously. First, let’s look at the Northern Hemisphere data updated to 2010:
Not only does it remain the case that no positive trend in these intense cyclones has occurred in the Northern Hemisphere, the negative trend has actually become larger than previously. Before it was obvious that the trend’s difference from zero was probably insignificant, I won’t just eyeball it this time since it is now more noticeable, but I have not verified either that it is or is not different from zero statistically.
Looking globally, we have the problem that while in the Northern Hemisphere a cyclone season sits nicely within a year, the Southern Hemisphere basins straddle the boundary between years because the seasons are inverted there. So there are two possible ways to add the time series together to get global data: Either add all the cyclones from a season to the Northern Hemisphere cyclones from the start year of the season, or the end year. Interestingly, which of these options you chose actually determines whether there is a slight increase or no trend at all. That any supposed “trend” is sensitive to such a subjective (as far as I can tell) decision does not give one confidence that such a trend is “significant” in any meaningful sense. Nevertheless the data say what they say. To me it’s clear that there is no dramatic increase in intense cyclone activity going on.
As can be seen above, the global trend in category 4 and 5 tropical cyclones is only positive (and even then rather small) if one decides to add their totals to the Northern Hemisphere’s in a particular manner. This suggests that claims of globally increasing intense tropical cyclones are overblown at best.
Please refer to this post for information on the methodology and references relevant to the analysis in this post. Data originate from their official reporting centers.