Thursday, September 13, 2018

Blaming Trump for Hurricanes

I keep thinking of Pat Robertson blaming hurricanes on sexual immorality.  But NOAA points out:

Figure 1: Atlantic tropical storms lasting more than 2 days have not increased in number. Storms lasting less than two days have increased sharply, but this is likely due to better observations. Figure adapted from Landsea, Vecchi, Bengtsson and Knutson (2009, J. Climate)
There has been a very pronounced increase in the number of tropical storms and hurricanes in the Atlantic since the late-1980s. However, to gain insight on the influence of climate change on Atlantic tropical storm and hurricane frequency, we must focus on longer (> 100 yr) records of Atlantic hurricane activity since very strong year-to-year and decade-to-decade variability appears in records of Atlantic tropical cyclones. If greenhouse warming causes a substantial increase in hurricane activity, then the century scale increase in global and tropical Atlantic SSTs since the late 1800s should have been accompanied by a long-term rising trend in measures of Atlantic hurricanes activity.
Existing records of past Atlantic tropical storm numbers (1878 to present) in fact do show a pronounced upward trend, correlated with rising SSTs (see Figs. 1 and 9 of Vecchi and Knutson 2008). However, the density of reporting ship traffic over the Atlantic wasrelatively sparse during the early decades of this record, such that if storms from the modern era (post 1965) had hypothetically occurred during those earlier decades, a substantial number would likely not have been directly observed by the ship-based “observing network of opportunity.” We find that, after adjusting for such an estimated number of missing storms, there is a small nominally positive upward trend in tropical storm occurrence from 1878-2006. But statistical tests reveal that this trend is so small, relative to the variability in the series, that it is not significantly distinguishable from zero (Figure 2). Thus the historical tropical storm count record does not provide compelling evidence for a greenhouse warming induced long-term increase.

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