We anticipate that it may take a decade for the observations to clarify the situation as to whether the hypothesis has predictive power. – Curry et al. 2006
So . . . another 10 years, what will that bring? Well, this time I won’t predict that this will be sorted out in another 10 years. —Judith Curry 2015
My first substantive post at Climate Etc. was Hurricanes and global warming: 5 years post Katrina. I recall spending two weeks (!) working on that post (its a very good post, if I say so myself). I no longer actively research this topic, although I do keep up with the literature.
In this post, I review the recent observationally-based literature on the topic of climate change and hurricanes, and in particular address the issue of sorting out natural variability from human caused climate change in terms of impacts on any changes in hurricanes; an issue that i raised in my 2006 publication Mixing politics and science in testing the hypothesis that greenhouse warming is causing a global increase in hurricane intensity.
For a quick update, see an an article by CarbonBrief that includes some interviews with hurricane/climate scientists. Also note a blog post by Kerry Emanuel at the CCNF Climate change and Hurricane Katrina: what have we learned?
Let me begin here with an update from some of the antagonists in the 2005/2006 hurricane wars – new papers by Chris Landsea and Phil Klotzbach (protégée of Bill Gray) and Greg Holland.
Landsea and Klotzbach
Phil Klotzbach and Chris Landsea have a new paper in press at J. Climate:
Extremely Intense Hurricanes: Revisiting Webster et al. (2005) after 10 Years
Abstract. Webster et al. (2005) documented a large and significant increase in both the 23 number as well as the percentage of Category 4-5 hurricanes for all global basins from 24 1970-2004, and this manuscript examines if those trends have continued when including 25 ten additional years of data. In contrast to that study, as shown here, the global frequency of Category 4-5 hurricanes has shown a small, insignificant downward trend while the percentage of Category 4-5 hurricanes has shown a small, insignificant upward trend between 1990 and 2014. Accumulated Cyclone Energy globally has experienced a large and significant downward trend during the same period. We conclude that the primary reason for the increase in Category 4-5 hurricanes noted in observational datasets from 1970 to 2004 by Webster et al. was due to observational improvements at the various global tropical cyclone warning centers, primarily in the first two decades of that study.
Their main figure:
Their argument for ignoring data prior to 1990:
The mid to late 1970s heralded the advent of geostationary coverage around much of the world with the launching of GOES-1, 164 Meteosat-1, and GMS-1. However, the North (and South) Indian Ocean lacked direct geostationary satellite data until 1989 with the launching of Meteosat-5 (Knapp and Kossin 2007). Consequently, the archived best track data from JTWC only reports one Category 4-5 hurricane from 1970-1989 for the North Indian Ocean, whereas, during the most recent twenty-year period from 1995-2014, 13 Category 4-5 hurricanes have been observed. Landsea et al. (2006) identified several missed Category 4-5 hurricanes before 1990, which were instead considered to be weaker TCs. After the advent of geostationary satellites, techniques we re developed and refined for interpreting the intensity from satellite imagery. In particular, the Dvorak Technique – a position and intensity pattern recognition scheme – was first developed in the early 1970s for visible imagery (Dvorak 1975) and later revised to include infrared imagery (Dvorak 1984). The adaptation of this tool globally became standard during the 1980s once the Regional Specialized Meteorological Centers were established for monitoring and forecasting tropical cyclones (Velden et al. 2006). In addition, operational responsibility for the northeast Pacific basin shifted from the Weather Service Forecast Office, Redwood City, California, to the National Hurricane Center following the 1987 season, which appears to have caused an artificial jump in 1988 in analyzed intensities between the two agencies (Todd Kimberlain, personal communication, 2015). Finally, the demise of extensive aircraft reconnaissance missions in the Northwest Pacific basin in 1987 likely led to a non negligible impact upon analyzed intensities. The efforts within the IBTrACS project (Knapp et al. 2010) have led to global TC data sets, but, while these data are now easily available, there has yet to be an internationally agreed-upon standardized global TC intensity database.
JC comment: The debate on the increase in % CAT45 hinges on whether the data from 1985-1989 is of useful accuracy. I concur that the global intensity prior to 1980 isn’t useful, but through the 1980’s the data become increasingly reliable. Missed Indian Ocean CAT45 should not have an overwhelming affect on the statistics, since Indian Ocean tropical cyclones constitute only 25% of global TCs. Prior to 1988, Northwest Pacific Basin intensities were arguably MORE accurate (aircraft reconnaissance) – NW Pac tropical cyclones constitute about 40% of global TCs.