The IPCC AR6 presents a strong body of scientific evidence that it is unequivocal that humans have caused the earth’s climate to warm, with a likely human contribution of 0.8 to 1.3 degrees Celsius to global mean temperature since the late 1800s. But what does this anthropogenic global warming mean for hurricane or tropical cyclone activity?
- Sea level rise – which human activity has very likely been the main driver of since at least 1971 according to IPCC AR6 – should be causing higher coastal inundation levels for tropical cyclones that do occur, all else assumed equal.
- Tropical cyclone rainfall rates are projected to increase in the future (medium to high confidence) due to anthropogenic warming and accompanying increase in atmospheric moisture content. Modelling studies on average project an increase on the order of 10-15% for rainfall rates averaged within about 100 km of the storm for a 2 degree Celsius global warming scenario.
- Tropical cyclone intensities globally are projected to increase (medium to high confidence) on average (by 1 to 10% according to model projections for a 2 degree Celsius global warming). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size. Storm size responses to anthropogenic warming are uncertain.
- The global proportion of tropical cyclones that reach very intense (Category 4 and 5) levels is projected to increase (medium to high confidence) due to anthropogenic warming over the 21st century. There is less confidence in future projections of the global number of Category 4 and 5 storms, since most modelling studies project a decrease (or little change) in the global frequency of all tropical cyclones combined.
Likelihood Statements
The terminology here for likelihood statements generally follows the conventions used in the IPCC assessments, i.e., for the assessed likelihood of an outcome or result:
- Very Likely: > 90%,
- Likely: > 66%
- More Likely Than Not (or Better Than Even Odds) > 50%
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