Data and conclusions linking more intense hurricanes to Global Warming:
Global Warming and Hurricanes
An Overview of Current Research Results
Last Revised: Sept. 20, 2018
https://www.gfdl.noaa.gov/global-warmin ... urricanes/
1. Summary Statement
Two frequently asked questions on global warming and hurricanes are the following:
• What changes in hurricane activity are expected for the late 21st century, given the pronounced global warming scenarios from IPCC models?
• Have humans already caused a detectable increase in Atlantic hurricane activity or global tropical cyclone activity?
The IPCC AR5 presents a strong body of scientific evidence that most of the global warming observed over the past half century is very likely due to human-caused greenhouse gas emissions. But what does this change mean for hurricane activity? Here, we address these questions, starting with those conclusions where we have relatively more confidence. The main text then gives more background discussion. “Detectable” change here will refer to a change that is large enough to be clearly distinguishable from the variability due to natural causes. Our main conclusions are:
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%
• Sea level rise–which very likely has a substantial human contribution to the global mean observed rise according to IPCC AR5–should be causing higher storm surge levels for tropical cyclones that do occur, all else assumed equal.
• Tropical cyclone rainfall rates will likely increase in the future due to anthropogenic warming and accompanying increase in atmospheric moisture content. Modeling 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 will likely increase 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 will likely increase 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 modeling studies project a decrease (or little change) in the global frequency of all tropical cyclones combined.
2. Global Warming and Atlantic Hurricanes
A. Statistical relationships between SSTs and hurricanes
Observed records of Atlantic hurricane activity show some correlation, on multi-year time-scales, between local tropical Atlantic sea surface temperatures (SSTs) and the Power Dissipation Index (PDI) —see for example Fig. 3 on this EPA Climate Indicators site. PDI is an aggregate measure of Atlantic hurricane activity, combining frequency, intensity, and duration of hurricanes in a single index. Both Atlantic SSTs and PDI have risen sharply since the 1970s, and there is some evidence that PDI levels in recent years are higher than in the previous active Atlantic hurricane era in the 1950s and 60s.
Model-based climate change detection/attribution studies have linked increasing tropical Atlantic SSTs to increasing greenhouse gases, but proposed links between increasing greenhouse gases and hurricane PDI or frequency has been based on statistical correlations. The statistical linkage of Atlantic hurricane PDI to Atlantic SST suggests at least the possibility of a large anthropogenic influence on Atlantic hurricanes. If this statistical relation between tropical Atlantic SSTs and hurricane activity is used to infer future changes in Atlantic hurricane activity, the implications are sobering: the large increases in tropical Atlantic SSTs projected for the late 21st century would imply very substantial increases in hurricane destructive potential–roughly a 300% increase in the PDI by 2100 (Figure 1a).