From NOAA’s Geophysical Fluid Dynamics Laboratory:
Global Warming and Hurricanes
An Overview of Current Research Results
1. Has Global Warming Affected Hurricane or Tropical Cyclone Activity?
Geophysical Fluid Dynamics Laboratory/NOAA
Last Revised: Mar. 17, 2017
A. Summary Statement
Two frequently asked questions on global warming and hurricanes are the following:
- Have humans already caused a detectable increase in Atlantic hurricane activity or global tropical cyclone activity?
- What changes in hurricane activity are expected for the late 21st century, given the pronounced global warming scenarios from current IPCC models?
In this review, we address these questions in the context of published research findings. We will first present the main conclusions and then follow with some background discussion of the research that leads to these conclusions. The main conclusions are:
- It is premature to conclude that human activities–and particularly
greenhouse gas emissions that cause global warming–have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. That said, human activities may have already caused changes that are not yet detectable due to the small magnitude of the changes or observational limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).
- Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average (by 2 to 11% according to model projections for an IPCC A1B scenario). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.
- There are better than even odds that anthropogenic warming over the next century will lead to an increase in the occurrence of very intense tropical cyclone in some basins–an increase that would be substantially larger in percentage terms than the 2-11% increase in the average storm intensity. This increase in intense storm occurrence is projected despite a likely decrease (or little change) in the global numbers of all tropical cyclones.
- Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones to have substantially higher rainfall rates than present-day ones, with a model-projected increase of about 10-15% for rainfall rates averaged within about 100 km of the storm center.
In figure 1 which they provide below, note in panel (a) and (b) how the
how high resolution model projections (green) are so much lower around 2100 than 24 other climate models. This suggests that even 80 years into the future, the PDI of tropical storms wont be outside of present observed natural variations
Vecchi et al. 2008 (PDF)
Synthesis and Summary for Atlantic Hurricanes and Global Warming
In summary, neither our model projections for the 21st century nor our analyses of trends in Atlantic hurricane and tropical storm counts over the past 120+ yr support the notion that greenhouse gas-induced warming leads to large increases in either tropical storm or overall hurricane numbers in the Atlantic. One modeling study projects a large (~100%) increase in Atlantic category 4-5 hurricanes over the 21st century, but we estimate that this increase may not be detectable until the latter half of the century.
Therefore, we conclude that despite statistical correlations between SST and Atlantic hurricane activity in recent decades, it is premature to conclude that human activity–and particularly greenhouse warming–has already caused a detectable change in Atlantic hurricane activity. (“Detectable” here means the change is large enough to be distinguishable from the variability due to natural causes.) However, human activity may have already caused some some changes that are not yet detectable due to the small magnitude of the changes or observation limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).
We also conclude that it is likely that climate warming will cause hurricanes in the coming century to be more intense globally and to have higher rainfall rates than present-day hurricanes. In our view, there are better than even odds that the numbers of very intense (category 4 and 5) hurricanes will increase by a substantial fraction in some basins, while it is likely that the annual number of tropical storms globally will either decrease or remain essentially unchanged. These assessment statements are intended to apply to climate warming of the type projected for the 21st century by IPCC AR4 scenarios, such as A1B.
The relatively conservative confidence levels attached to these projections, and the lack of a claim of detectable anthropogenic influence at this time contrasts with the situation for other climate metrics, such as global mean temperature. In the case of global mean surface temperature, the IPCC 5th Assessment Report (2013) 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.
Read the entire report here: https://www.gfdl.noaa.gov/global-warming-and-hurricanes/
h/t to Larry Kummer