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The Ability to Identify Category 4 and 5 Atlantic Hurricanes with Mid-20th-Century Tools
Hagen, A.B. and Landsea, C.W. 2012. On the classification of extreme Atlantic hurricanes utilizing mid-twentieth-century monitoring capabilities. Journal of Climate 25: 4461-4475.

The authors write that "previous studies state that there has been an increase in the number of intense hurricanes and [they] attribute this increase to anthropogenic global warming," while "other studies claim that the apparent increased hurricane activity is an artifact of better observational capabilities and improved technology for detecting these intense hurricanes." So who is right?

What was done
In an attempt to answer this important question, Hagen and Landsea focused on the ten most recent Category 5 hurricanes known to have occurred in the Atlantic Ocean, stretching from Hurricane Andrew in 1992 to Hurricane Felix of 2007. Placing these ten hurricanes into the context of the technology available from 1944-1953 - which was the first decade of aircraft reconnaissance - they determined how many of these ten recent Category 5 hurricanes likely would have been recorded as Category 5 if they had occurred during that earlier period, using only the observations that likely would have been available with then-existing technology and observational networks.

What was learned
The two U.S. researchers report that "there are likely to have been several Category 4 and 5 hurricanes misclassified as being weaker prior to the satellite era." They determined, for example, that "if the ten most recent Category 5 hurricanes occurred during the late-1940s period, only two of them would be considered Category 5 hurricanes (and three of ten for the early-1950s period)." In addition, they say that "three recent Category 4 hurricanes were identified that would likely not have been counted as major hurricanes if they had occurred during the late 1940s/1950s."

What it means
On the basis of their detailed analyses, Hagen and Landsea conclude that "counts of Category 4 and 5 hurricanes (at least through 1953 and likely beyond that year) are not nearly as reliable as they are today," and, therefore, they further conclude that "future studies that discuss frequency trends of Atlantic basin Category 4 and 5 hurricanes must take into account the undercount biases that existed prior to the geostationary satellite era due to the inability to observe these extreme conditions." And so it is that these latest findings pretty much take the wind out of the sails of those who have previously claimed that there has been an increase in the number of intense hurricanes in recent years, and who attribute this imaginary increase to imaginary anthropogenic-induced global warming.

Reviewed 26 December 2012