Paul Linsay contributes the following:
Using Landsea’s data from here, plus counts of 15 and 5 hurricanes in 2005 and 2006 respectively, I plotted up the yearly North Atlantic hurricane counts from 1945 to 2004 and added error bars equal to as is appropriate for counting statistics.
The result is in Figure 1.
Figure 1. Annual hurricane counts with statistical errors indicated by the red bars. The dashed line is the average number of hurricanes per year, 6.1.
There is no obvious long term trend anywhere in the plot. There is enough noise that a lot of very different curves could be well fit to this data, especially data as noisy as the SST data.
I next histogrammed the counts and overlaid it with a Poisson distribution computed with an average of 6.1 hurricanes per year. The Poisson distribution was multiplied by 63, the number of data points so that its area would match the area of the histogrammed data. The results are shown in Figure 2. The Poisson distribution is an excellent match to the hurricane distribution given the very small number of data points available. I should also point out that I did no fitting to get this result.
Figure 2. Histogram of the annual hurricane counts (red line) overlaid with a Poisson distribution (blue line) with an average of 6.1 hurricanes per year.
I conclude from these two plots that
- The annual hurricane counts from 1945 through 2006 are 100% compatible with a random Poisson process with a mean of 6.1 hurricanes per year. The trends and groupings seen in Figure 1 are due to random fluctuations and nothing more.
- The trend in Judith Curry’s plot at the top of this thread is a spurious result of the 11 year moving average, an edge effect, and some random upward (barely one standard deviation) fluctuations following 1998.