BLUF: 6.6 Conclusions
Convincing detection and attribution of individual extreme weather events such as hurricanes requires:
- a very long time series of high-quality observations of the extreme event
- an understanding of the variability of extreme weather events associated with multi-decadal ocean oscillations, which requires at least a century of observations
- climate models that accurately simulate both natural internal variability on timescales of years to centuries and the extreme weather events
Of the four hurricanes considered here, only the rainfall in Hurricane Harvey passes the detection test, given that it is an event unprecedented in the historical record for a continental U.S. landfalling hurricane. Arguments attributing the high levels of rainfall to near record ocean heat content in the western Gulf of Mexico are physically plausible. The extent to which the high value of ocean heat content in the western Gulf of Mexico can be attributed to manmade global warming is debated. Owing to the large interannual and decadal variability in the Gulf of Mexico (e.g. ENSO), it is not clear that a dominant contribution from manmade warming can be identified against the background internal climate variability (Chapter 4).