Mann Made Hurricanes

By Paul Homewood

 

 

In an interview last week, Michael Mann tells us

One of the more robust predictions is that in the Atlantic, hurricane intensities have increased and they will likely continue to increase, and so, it’s part of a trend, Katrina, the record season of 2005 was part of a trend towards more destructive storms…

Joe Bastardi has subsequently ripped to pieces this latest piece of nonsense from Mann, who is described by the interviewer as one of the giants of climate science. (The other was Joe Romm, which at least proves greenies have a sense of humour). And we should not really kick a man when he’s down, but what the heck.

So here’s a few more thoughts to add to Joe’s.

 

 

1) According to the EPA’s Climate Change Indicators booklet

Over time, data collection methods have changed as technology has improved. For example, wind speed collection methods have evolved substantially over the past 60 years. How these changes in data gathering technologies might affect data consistency over the life of the indicator is not fully understood.

Put bluntly there is a historical problem with hurricane measurement due to the fact that in the early 1900s, only hurricanes striking land or observed from surviving boats were seen and named. Starting in the mid-20^th century, major hurricanes spotted from planes were counted and named. Since the satellite era, all hurricanes are spotted, counted and named regardless of size or duration.

2) NOAA scientist Chris Landsea tell us

 

Records of Atlantic basin tropical cyclones (TCs) since the late nineteenth century indicate a very large upward trend in storm frequency. This increase in documented TCs has been previously interpreted as resulting from anthropogenic climate change. However, improvements in observing and recording practices provide an alternative interpretation for these changes: recent studies suggest that the number of potentially missed TCs is sufficient to explain a large part of the recorded increase in TC counts. This study explores the influence of another factor—TC duration—on observed changes in TC frequency, using a widely used Atlantic hurricane database (HURDAT). It is found that the occurrence of short-lived storms (duration of 2 days or less) in the database has increased dramatically, from less than one per year in the late nineteenth–early twentieth century to about five per year since about 2000, while medium- to long-lived storms have increased little, if at all. Thus, the previously documented increase in total TC frequency since the late nineteenth century in the database is primarily due to an increase in very short-lived TCs.

The authors also undertake a sampling study based upon the distribution of ship observations, which provides quantitative estimates of the frequency of missed TCs, focusing just on the moderate to long-lived systems with durations exceeding 2 days in the raw HURDAT. Upon adding the estimated numbers of missed TCs, the time series of moderate to long-lived Atlantic TCs show substantial multidecadal variability, but neither time series exhibits a significant trend since the late nineteenth century, with a nominal decrease in the adjusted time series.

Thus, to understand the source of the century-scale increase in Atlantic TC counts in HURDAT, one must explain the relatively monotonic increase in very short-duration storms since the late nineteenth century. While it is possible that the recorded increase in short-duration TCs represents a real climate signal, the authors consider that it is more plausible that the increase arises primarily from improvements in the quantity and quality of observations, along with enhanced interpretation techniques. These have allowed National Hurricane Center forecasters to better monitor and detect initial TC formation, and thus incorporate increasing numbers of very short-lived systems into the TC database.

 

3) A paper by Gabrielle Villarini finds

The number of North Atlantic tropical storms lasting 2 days or less exhibits a large increase starting from the middle of the 20th century, driving the increase in recorded number of tropical storms over the past century. Here we present a set of quantitative analyses to assess whether this behavior is more likely associated with climate variability/change or with changes in observing systems. By using statistical methods combined with the current understanding of the physical processes, we are unable to find support for the hypothesis that the century-scale record of short-lived tropical cyclones in the Atlantic contains a detectable real climate signal. Therefore, we interpret the long-term secular increase in short-duration North Atlantic tropical storms as likely to be substantially inflated by observing system changes over time. These results strongly suggest that studies examining the frequency of North Atlantic tropical storms over the historical era (between the 19th century and present) should focus on storms of duration greater than about 2 days. 

4) And a study by NOAA in 2005 states

As a result, the North Atlantic experiences alternating decades long (20 to 30 year periods or even longer) of above normal or below normal hurricane seasons. NOAA research shows that the tropical multi-decadal signal is causing the increased Atlantic hurricane activity since 1995, and is not related to greenhouse warming.

In other words the Atlantic Multi Decadal Oscillation (AMO).

 

 

5) And in another paper by Chris Landsea, we find that

contrary to many expectations that globally tropical cyclones may be becoming more frequent and/or more intense due to increasing concentrations of greenhouse gases, regionally the Atlantic basin has in recent decades seen a significant trend of fewer intense hurricanes and weaker cyclones overall. In addition, the maximum intensity reached in each year has shown no appreciable change.

6) And finally the National Hurricane Centre have produced this analysis of US hurricane strikes.

 

US Hurricane Strikes By Decade

Decade	All Hurricanes	Major (Category 3-5)
1851-60	19	6
1861-70	15	1
1871-80	20	7
1881-90	22	5
1891-00	21	8
1901-10	18	4
1911-20	21	7
1921-30	13	5
1931-40	19	8
1941-50	24	10
1951-60	17	8
1961-70	14	6
1971-80	12	4
1981-90	15	5
1991-00	14	5
2001-10	19	7
TOTAL	283	96
Average per Decade	17.7	6.0

 

Again we see the effect of the AMO, but clearly the last decade is quieter than the 1930-60 period when the AMO was last positive, both in terms of total numbers and in terms of intensity.

 

Mann should know all of this, so is he being dishonest or is he simply incompetent?