The Question Everyone Is Asking
Every time a major hurricane makes landfall, the question follows immediately: is climate change making hurricanes worse? The answer, as with most questions at the intersection of weather and climate, is more specific and more nuanced than a simple yes or no — and understanding the specifics matters for interpreting hurricane forecasts, understanding the risks of the current season, and making sense of what the next several decades of hurricane seasons may look like.
The science on climate change and tropical cyclones has advanced substantially in the past decade, moving from early, cautious statements about uncertain future projections to a clearer — if still incomplete — picture of observed changes that are already occurring and projected changes that the research community has identified with growing confidence. What the science shows is not that hurricanes are universally worse in every measurable way, but that specific aspects of hurricane behavior are changing in specific, physically understood ways that have significant implications for the populations in their path.
What Is and Isn’t Changing: The State of the Science
Rapid intensification is becoming more common. Rapid intensification — defined as an increase of 35 mph or more in maximum sustained winds within 24 hours — is one of the most dangerous aspects of hurricane behavior for coastal communities because it can convert a storm that appeared manageable into a catastrophic threat in less than a day. Research using historical records shows a statistically significant increase in rapid intensification events in the Atlantic basin over recent decades, particularly in the last 30 years. The physical mechanism is straightforward: warmer sea surface temperatures provide more energy for hurricane intensification, and the upper ocean heat content — the depth of warm water, not just the surface temperature — has increased as the ocean absorbs the majority of the excess heat trapped by greenhouse gas forcing. A hurricane passing over a deeper warm layer sustains its intensification longer rather than churning up cooler water from below that would otherwise limit the process.
Harvey, Irma, Maria, Michael, Laura, Ida — the most destructive Atlantic hurricanes of the past decade share a common characteristic: all underwent rapid intensification before or near landfall, catching populations and emergency managers with insufficient time to respond to their actual intensity at landfall. The statistical signal in rapid intensification rates is one of the more robust findings in the observed hurricane-climate change literature.
Rainfall rates are increasing. A warmer atmosphere holds more water vapor — approximately 7 percent more per degree Celsius of warming, following the Clausius-Clapeyron relationship. More water vapor in the atmosphere means more water available for precipitation in any storm system, including tropical cyclones. The research on hurricane rainfall intensification is clear and consistent: tropical cyclones are producing more rainfall per storm than they did in previous decades, and the projected increase continues as warming proceeds.
Hurricane Harvey’s catastrophic rainfall — up to 60 inches in the Houston area in 2017 — was the subject of one of the first rigorous hurricane attribution studies to examine rainfall intensification. The study found that Harvey’s extreme rainfall was approximately three times more likely and 15 percent more intense than it would have been in the climate of the late 20th century. The physical mechanism — more atmospheric moisture available to the storm — is well-understood and applies to every tropical system, making increased rainfall one of the most confident projections in the tropical cyclone-climate change literature.
Storms are moving more slowly. Research published in 2018 found that the average forward speed of tropical cyclones had decreased by approximately 10 percent globally over the past 70 years, with larger decreases in some regions. Slower-moving storms deliver more rainfall to any given location — a storm that moves at 5 mph rather than 15 mph spends three times as long over any given point, delivering three times as much rainfall. Harvey’s catastrophic rainfall was amplified by the storm’s near-stall over the Houston area; the slow movement that allowed 60 inches to fall in one location reflects both the storm’s specific behavior and the broader trend toward slower tropical cyclone movement.
Storms are intensifying at higher latitudes. Tropical cyclones historically weakened as they moved poleward and encountered cooler sea surface temperatures and higher wind shear. As the oceans warm, the region of water warm enough to support tropical cyclone development and maintenance extends poleward, allowing storms to maintain intensity farther from the tropics than they historically could. This poleward expansion of the hurricane threat zone has implications for communities farther north that have historically been less likely to experience major hurricane conditions — the New England coast, for example, or the mid-Atlantic states — whose infrastructure, building codes, and cultural preparedness may reflect historical hurricane frequency rather than the frequency that a warmer climate produces.
What Is Not Clearly Changing
Two aspects of the hurricane-climate relationship are frequently cited but are not supported by the current scientific evidence with the same confidence as the changes described above.
Total hurricane frequency is not clearly increasing. The number of named Atlantic storms per season shows high year-to-year variability driven by factors including the El Niño-Southern Oscillation, Atlantic sea surface temperature patterns, and the Atlantic Multidecadal Oscillation. The long-term trend in total storm count is not statistically robust, and some research suggests that while the number of intense major hurricanes may be increasing as a fraction of all storms, the total count of storms across all categories is not systematically rising.
Individual event attribution remains case-by-case. Climate change altered the probability and intensity of Harvey’s rainfall, the rapid intensification of Ida, and the intensity of specific storms in ways that attribution science can now quantify — but it is not accurate to say that any specific hurricane “was caused by” climate change. Climate change changes the conditions in which all hurricanes operate, altering their characteristics in statistically detectable ways, but individual storms arise from specific meteorological conditions that vary independently of the long-term climate trend.
The Rapid Intensification Problem
Of all the climate-related changes in hurricane behavior, rapid intensification most directly challenges the current warning and evacuation system. The NHC advisory products covered in the 7/5 piece are designed to provide 24 to 48 hours of useful warning before major hurricane conditions arrive. When a storm intensifies from Category 1 to Category 4 in 24 hours — as Michael did before its Florida Panhandle landfall in 2018 — that warning window is largely consumed by the intensification itself, leaving communities with inadequate time to evacuate based on the storm’s actual landfall intensity.
The Hurricane Hunters piece covered how aerial reconnaissance provides the central pressure measurements that inform intensity estimates. Improving rapid intensification forecasting — predicting not just whether intensification will occur but when, how fast, and to what final intensity — is one of the most active areas of current hurricane research, driven precisely by the recognition that rapid intensification is both increasing in frequency and represents the most dangerous gap in the current warning system.
What the Next Decades Look Like
The research community’s projections for hurricane behavior in a warmer climate — based on physical modeling, historical analysis, and attribution science — point consistently in a few directions:
The proportion of intense hurricanes — Category 4 and 5 — is projected to increase even if total storm frequency does not, because warmer sea surface temperatures and higher atmospheric moisture content favor the development of the most intense storms. A given hurricane season may produce a similar number of named storms but a higher fraction of them reaching major hurricane status.
Rainfall rates will continue to increase in proportion to atmospheric moisture content, which scales with temperature. The storms of 2050 will, on average, produce more rainfall than the storms of today, and the extreme rainfall events that produce catastrophic flooding — like Harvey — will become more frequent.
The combination of higher sea levels — which raise the baseline upon which storm surge is added — and potentially more intense storms means that storm surge flooding will affect areas and elevations that current flood maps designate as lower-risk. FEMA flood map updates lag behind the pace of sea level rise, meaning current flood zone designations systematically underestimate risk in coastal areas.
The Season Ahead, in Context
The hurricanes of the current season will develop in an ocean that is warmer than it was in 1950, producing conditions more favorable for rapid intensification and more extreme rainfall than the historical record reflects. This doesn’t mean every storm will be catastrophic or that the season will necessarily be record-breaking — year-to-year variability remains large, and factors including El Niño, wind shear patterns, and the specific track of individual storms determine outcomes as much as baseline climate does.
What it means is that the upper end of what any given storm can do is higher than it was in previous decades, and that the storms that do intensify rapidly and produce extreme rainfall are doing so in an environment that makes those outcomes more likely. Preparing for the peak of hurricane season — as the mid-season storm prep piece covered — requires accounting for what the season’s storms can realistically become, not just what historical averages suggest they will.
