I think we are on the same wavelength here, just arguing two different sides. I am not convinced there is such a thing as an AMO signal, though neither am I convinced that there is such a strong anthropogenic global warming signal at least to the point that it significantly influences Atlantic activity. The best papers on that topic show 35-40% variance in overall activity explained by warming SSTs; this inherently suggests other factors are at play. In the Atlantic, they show a statistically significant correlation with reduced shear, responsible for about the same amount of variance.
What causes that reduced shear? What accounts for the rest of the variance? Sure, warmer SSTs put you at a higher baseline for activity, but they don't put you at a season with almost 3 times as much activity as normal. The AMO does not explain it, nor does anthropogenic global warming. Was the NOAA slide a factor of their expected atmospheric conditions, or was it more of a result of the AMO (as implied)? A straight warming of the SSTs does not bring about such broad changes to the pattern; other factors that they are not discussing, such as a neutral or weak La Nina (as thought then) state, might do that, however. We need to have better attribution as to what is causing things to be the way they are.
ACE and, from other works, integrated power dissipation (similar to ACE, except a cubic value rather than a squared value of wind) are both well correlated to SSTs, but still only explain that 35-40% of the variance. For this I refer back to the Emanuel works from 2005 as well as the Sriver-Huber paper from just a month or so ago. Can it be attributed to the AMO? There's evidence that the AMO signal is actually the opposite of what it should be to strongly enhance activity. Is the AMO an artifact of poor data manipulation? Perhaps. Could all of the factors be tied together by some underlying factor? Sure. I'm just arguing that neither side really know enough to say one way or the other and that, given the evidence that is out there, it is not likely that the changes we saw in 2005 in the Atlantic can br prescribed to a single variable...particularly given that such a signal is not nearly as strong or even opposes trends in Pacific basins (see Johnny Chan's work for more on this).
Global warming can't be a localized factor to the Atlantic; other factors must be at play. Specifying those other factors will be key for advancing our understanding of the hurricane and climate system. Maybe someday we'll see such a study performed; it is the next logical step. Then, AMO or not, we'll have some more definitive answers.
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