I’m quite happy to publish other people’s criticisms of topical and semi-topical papers. Judith Curry has sent in the following comments on Klotzbach et al, (mentioned on roadmap), abridged by her from a previous post on the tropical listserv, responding to specific talking points on the Klotzbach paper that were posted on Gray’s website.
If the increases in TC activity found by Emanuel  over the past 30 years (based on data from 1975-2004) and Webster et al.  over the past 35 years (based on data from 1970-2004) are robust, one would expect to see similar trends over the shorter time span evaluated in this paper (1986-2005), especially since SST increases have accelerated in the past twenty years.
This is flawed logic, fallacy of distribution of the divisional type, whereby you cannot assume that what is true of the class is true of its members. You cannot dice up the 35 year period and expect the same statistical relationships to be present in each segment. 35 years is marginally short to identify a statistically significant trend (people who criticized our study because the length of the data record is too short raised a legitimate point). 20 years is definitely too short. The reason for this is that both the atlantic and pacific have large multidecadal modes. if you pick a period that is too short, what you are seeing is one piece of the mode. The Pacific has a big multidecadal mode that peaked around 1990, so most of the data outside the N. Atlantic is biased by this particular sampling.
There is considerable disagreement about the data quality before the middle 1980s. Best track datasets for the Western North Pacific, the North Indian Ocean and the Southern Hemisphere before 1985 should be “used with great caution” according to the authors of the best track dataset.
No rigorous uncertainty analysis has been conducted to date. the data in the western North Pacific, which has 40% of global hurricanes/ typhoons, actually DECREASES in quality after 1987, when aircraft reconnaissance flights were discontinued in this region. so the arguments about choosing only the data since 1985 owing to better data quality is substantially flawed
With regards to ACE, there has been a large increase in ACE in the North Atlantic basin since 1986. There has been a large decrease in ACE in the Northeast Pacific basin since 1986. All other basins show small upward or downward trends. Globally, there has been a slight increasing trend from 1986-2005; however, if only the past sixteen years are evaluated (1990-2005), there has actually been a slight decreasing trend.
the ACE confounds the number of hurricanes with the intensity (ACE effectively includes both). There are several ocean basins where the number of cyclones is actually decreasing, which would lead to a decrease in ACE (while at the same time showing an increase in intensity). See also #1, re problems of just looking at a 20 yr time period.
With regards to the number of Category 4-5 hurricanes, there has been a large increase in North Atlantic storms but also a large decrease in Northeast Pacific storms. When these two regions are summed together, there has been virtually no increase in Category 4-5 hurricanes (i.e., 47 Cat. 4-5 hurricanes from 1986-1995 and 48 Cat. 4-5 hurricanes from 1996-2005). For the globe, there has been an approximate 10% increase in Category 4-5 storms from 1986-1995 to 1996-2005; however, most of this increase occurred from the late 1980s to the early part of the 1990s in the Southern Hemisphere where some data quality issues may have still been present. There has been very little change in the number of Category 4-5 hurricanes since 1990, which is an agreement with Figure 4, panel A from Webster et al. .
The more relevant metric would the percentage of cat 4-5 hurricanes (which is what Webster et al. focused on). If the total number of hurricanes is decreasing outside the N. Atlantic, then you would expect some decrease in Cat 4-5. The fact that you still get an increase in cat 4-5 hurricanes implies a substantial increase in the % of Cat 4-5. See also #1, re problems in looking at just a 20 year time period.
There is a positive correlation (significant at the 99% level) between SSTs and ACE values and Category 4-5 hurricanes for both the Atlantic and the Northeast Pacific basins. However, correlations between SSTs and ACE values and Category 4-5 hurricanes for all other basins (i.e., Northwest Pacific, North Indian, South Indian and South Pacific) are not significant.
This argument was debunked by the Hoyos et al. paper recently published in science. While other factors such as wind shear etc are important determinants of the intensity of individual storms and even for seasonal average intensity (owing to factors such as El Nino), there is no trend in wind shear, humidity, etc. The analysis of Hoyos et al. clearly shows that the global increase in intensity shares information with the global trend in tropical sea surface temperature (and not wind shear, etc.)