Hurricanes update

Via the indefatigable het, I discover a new Statement on Tropical Cyclones and Climate Change, Submitted to CAS-XIV under Agenda Item 7.3 by Dr G. B. Love, Permanent Representative for Australia Prepared by the WMO/CAS Tropical Meteorology Research Program, Steering Committee for Project TC-2: Scientific Assessment of Climate Change Effects on Tropical Cyclones. February 2006.

Iinterestingly this statement features, among others, both Kerry Emanuel (of paper-in-Nature fame) and Chris Landsea (of Hurricane-expert-flouncing-out-of-IPCC fame) as authors, and may have been a deliberate effort to get an agreed statements from what have been perceived as opposing camps. Mind you, I'm not privy to any of the inside info so I'm just guessing.

So... having noted the previous (1998) statement; the active 2004 and 5 seasons; and the IPCC TAR evidence for warming; and the fact that the press may have got carried away asserting a GW-hurricanes link (but not the converse, that some got carried away denying the link), we come on to:

• No single high impact tropical cyclone event of 2004 and 2005 can be directly
  attributed to global warming, though there may be an impact on the group as a
  whole; [my comment: fair enough; this is essentially what RealClimate said, so it must be right :-) ]
• Emanuel (2005) has produced evidence for a substantial increase in the power of tropical cyclones (denoted by the integral of the cube of the maximum winds over time) during the last 50 years. This result is supported by the
  findings of Webster et al (2005) that there has been a substantial global increase (nearly 100%) in the proportion of the most severe tropical cyclones (category 4 and 5 on the Saffir-Simpson scale), from the period from 1970 to
  1995, which has been accompanied by a similar decrease in weaker systems. [comment: OK, thats the next step. But now...]
• The research community is deeply divided over whether the results of these studies are due, at least in part, to problems in the tropical cyclone data base. Precisely, the historical record of tropical cyclone tracks and intensities is a byproduct of real-time operations. Thus it's accuracy and completeness changes continuously through the record as a result of the continuous changes and improvements in data density and quality, changes in satellite remote sensing retrieval and dissemination, and changes in training. In particular a step-function change in methodologies for determination of satellite intensity occurred with the introduction of geosynchronous satellites in the mid to late 1970's. [comment: yes indeed. This is Fair Enough as well. There is a disagreement, and I guess we shouldn't pretend otherwise. Quite how deep it is, or what the numbers and reputations on each side are, I don't know]
• The division in the community on the Webster et al and on the Emanuel papers is not as to whether Global Warming can cause a trend in tropical cyclone intensities. Rather it is on whether such a signal can be detected in the historical data base... [good point. Most people will accept that there *can* be an effect; its the detecting of it thats tricky]
• Whilst the existence of a large multi-decadal oscillation in Atlantic tropical cyclones is still generally accepted, some scientists believe that a trend towards more intense cyclones is emerging. This is a hotly debated area for
  which we can provide no definitive conclusion. It is agreed that there is no evidence for a decreasing trend in cyclone intensities [Fair again I guess]

They also make a point that Roger Pielke has frequently (and in my view correctly) made at Prometheus, that While demographic trends are the dominant cause of increasing damage by tropical cyclones, any significant trends in storm activity would compound such trends in damage. (RP's point is the first bit but I doubt he'd object to the second). RP has some new FAQs up, conveniently one provides his view of Hurricanes and Global Warming with links to his stuff.