Roger Pielke pointed out that Holland and Webster have presented a PPT presentation posted up at UCAR (the home of IPCC WG1), the content of which is relevant to recent discussions at climateaudit and prometheus. The entire presentation is about data problems relating to storm trends in the eastern Atlantic and to landfall hurricanes, topics discussed at length at our respective sites.
The presentation is entitled “Heightened Tropical Cyclone Activity in the North Atlantic: Natural Variability or Climate Trend?” It asks: “Where have the Increases Occurred?” and reports:
Increases have occurred in all regions except the western Caribbean and southern Gulf of Mexico, but the largest proportional increases have been in the eastern Atlantic.
They ask: “Can Eastern Atlantic trends be due largely to data errors?” and answer:
There is little doubt that the eastern region was poorly observed in earlier years, but there are other factors; several studies have shown independent relationships, eg:
- Kossin and Vitmer (2007) have shown that there is a close relationship between positive phases of the AMM and the eastward extension of the genesis region; and
- Mann and Emanuel (2006) have shown that the AMM is potentially increasing because of Greenhouse Warming;
- We have shown a strong and stable relationship between frequency and SSTs;
They go on to ask: Can Landfalling Storms be used to infer Missing Oceanic Data? noting that:
The high proportion of landfalling storms in the pre-satellite era has been used to imply poor observations of cyclones in the eastern Atlantic (e.g. Solow and Moore, 2002, Landsea 2006).
They then propose a boundary line between east and west Atlantic about which they state:
We assume that all cyclones that cross to the left of the black line were highly likely to have been observed in some form.
Note that this says nothing about how accurate the genesis points are or the observed intensity, just whether they were known to have existed. …
Using the proximity to land and ship route approach implies that almost all storms were within a good observing area for some part of their life. Note the steady increase of non-landfall storms, implying that this has a real component.
They conclude the following:
Maximum Potential Error Prior to 1960 is < ~1 storm per year (or around 6% prior to 1960), which agrees with the assessment by Neumann (1999).
Most of the potential error impact is on tropical storms: ~0.5 per year (10%) prior to 1945;
Minor hurricanes: ~0% error;
Major hurricanes: <10% per year.
- The current Atlantic data base indicates a substantial trend in tropical cyclones and hurricanes and both a multidecadal oscillation and trend in major hurricanes;
- The trend is strongly related to Atlantic SST and thus to Greenhouse Warming;
- This trend is robust to all known potential problems with the data base,
At some point, I’ll try to wade through what they’ve done. As a quick comment, you’ll notice that they keep repeating that everything is strongly significant and that much of the rhetorical force derives from repetition of the comment, rather like an incantation. Likewise, the incantation that the trend is “strongly related to Atlantic SST and thus to Greenhouse Warming” – dare I say stronnnnngggg-ly related – whether or not the statement is true – is not actually demonstrated in the presentation, merely asserted.