Climate Shift Index: Tropical Cyclones
Climate change is warming oceans worldwide, and that added heat is fueling stronger hurricanes. The Climate Shift Index: Tropical Cyclones (Tropical Cyclone CSI), launched in 2025, uses the Climate Shift Index: Ocean and new peer-reviewed methods to show how much climate change has added to the strength of a storm’s winds.
Jump to the Frequently Asked Questions
Looking for information about the influence of climate change on other types of weather? Head to the Climate Shift Index (air temperatures) or Climate Shift Index: Ocean.
How the Tropical Cyclone CSI works
The Climate Shift Index: Tropical Cyclones (Tropical Cyclone CSI) quantifies the impact of climate change on a storm's intensity. More specifically, the system calculates the increase (or decrease) in a storm’s wind speeds because of climate change-warmed ocean waters and tropical climate warming.
Note: We refer to both "tropical cyclones" and "hurricanes" below — "tropical cyclone" describes the broader storm category, while "hurricane" applies to those occurring in the North Atlantic and Northeast Pacific.
This system is built on the foundation of our Ocean CSI tool, which shows daily sea surface temperatures across the globe and quantifies how human-caused climate change has increased (or decreased) the likelihood of those temperatures.
In addition to tracking ocean temperatures, the map tool also tracks hurricanes from formation to landfall, allowing users to see where a storm is headed, how warm the ocean is beneath it, and how that climate-driven warmth is affecting its intensity.
As the planet continues to warm, hurricanes are expected to become more intense, and thus more damaging. Understanding the growing role climate change plays in each storm is critical for informing emergency planning, insurance, adaptation, and public awareness.
How to access and use the data
Climate Central is compiling real-time data to tell the climate change story behind every named storm of the 2025 Atlantic hurricane season.
As a storm forms and develops, you can use our data and visuals to show how climate change is influencing ocean temperatures that fuel tropical cyclones and how those temperatures are influencing the storm’s intensity. This data is free and available to anyone — including journalists, meteorologists, scientists, emergency managers, and policymakers.
You can find this data on:
The Ocean CSI map tool (toggle on “Show tropical cyclones”)
The story page for each storm (coming soon). (Sign up for Climate Matters to receive these timely analyses.)
Downloadable graphics to be used on TV, social media, and wherever else you’d like to share them.
How the science works
The methods beneath the calculation of the Tropical Cyclone CSI system are described in brief here. You can find our more detailed, peer-reviewed methodology in Human-caused ocean warming has intensified recent hurricanes (Gilford et al, 2024). You can also find details of how we implemented these approaches here.
To understand how much human-caused climate change has intensified recent hurricanes, we start with Climate Shift Index: Ocean (Ocean CSI) data, which calculates how much carbon pollution has warmed the ocean waters over which hurricanes form. This approach is based on peer-reviewed research published in 2024.
Then, using the Gilford et al., 2024 hurricane attribution framework, we estimate the degree to which a specific hurricane has intensified in response to attributable ocean warming. The method calculates how human-caused ocean warming changes a storm’s “potential intensity” — the theoretical maximum wind speed that a storm’s environment can support. We also consider how climate warming in the tropics could act to stabilize the atmosphere. A more stable atmosphere would decrease hurricane intensities, partially offsetting the total ocean warming effect. In Gilford et al., 2024, this method is referred to as nonlocal damping. Together, these effects are combined to calculate an attributable shift in potential intensity
Using the known relationship between potential intensity and observed intensity, the system computes what the wind speeds would have been in a world without human-caused climate change. We call this the counterfactual hurricane intensity.
The difference in wind speed between the estimated counterfactual and known observed intensity is the change in hurricane intensity attributable to human-caused ocean warming (reported in miles per hour). In other words, this is how much stronger each hurricane became due to climate change-driven ocean and atmospheric warming.
We consider all storms in the Atlantic that reach at least Category 1 strength (≥74 mph).
FAQ #
Tropical cyclone attribution science — which enables us to quantify the influence of climate change on tropical cyclones such as hurricanes — is a rapidly evolving field. In recent years, scientists have developed peer-reviewed methodologies to directly quantify the influence of human-caused climate change on storm intensities.
Key developments include Climate Central’s Climate Shift Index: Ocean (Ocean CSI), which uses observational and climate model data to link warmer sea surface temperatures to climate change and is based on peer-reviewed science. Other advances include a better understanding of how increases in potential intensity affect observed intensities, improved climate and storm modeling, and the strong emergence of the climate signal: global temperatures have risen by approximately 1.3°C since the pre-industrial period and 0.5°C since 2000.
Our system provides data on how climate change-driven ocean warming has influenced a storm once it reaches tropical storm status. This is when it receives a name from the World Meteorological Organization (WMO). Once a storm reaches at least Category 1 strength, our system provides data on how climate change is influencing wind speeds.
Currently, our system only analyzes data for tropical storms and hurricanes that form in the Atlantic basin. We plan to analyze data for other basins in the near future.
We make an early estimate of the climate change influence on a hurricane as soon as the National Hurricane Center forecasts the storm’s peak strength. As the storm develops, we update this estimate based on its environment and life cycle. Once the storm is over, we share a final estimate of climate change’s influence.
Once the National Hurricane Center forecasts the storm’s peak strength, we can use that forecast data in our system to make an early estimate of the climate change influence.
Our system uses ocean temperatures from the days just before a storm passes, rather than forecasts of ocean temperatures. This is because ocean temperatures in a specific location are relatively constant day to day, so temperatures from a day or two in the past are relatively predictive of the current ocean temperature. This also helps avoid signals generated by the storm itself, because a storm can cool surface waters as it passes over them.
Data about climate change’s effect on the storm will get updated as we get new storm information from the National Hurricane Center (NHC), at least every six hours. We expect a short delay (a few hours) between the time the NHC puts out new data and the time our analysis updates.
Tropical storm location, wind speed, and related data for the Atlantic Ocean basin come from the National Hurricane Center. Supplemental sea-surface temperature and atmospheric data for analyzing climate change’s influence on a tropical cyclone intensity come from NOAA’s Optimum Interpolation Sea Surface Temperature (OISST) and ECMWF’s ERA5 Reanalysis.
Warmer ocean temperatures are the main reason hurricanes are getting stronger, but they’re not the only factor. Changes in the atmospheric temperature, moisture, and wind patterns can also play a role. More specifically, as the atmosphere warms and holds more moisture, it stabilizes the tropical atmosphere, which can reduce hurricane intensities and offset the influence of warming oceans. Our analysis includes these combined effects to determine the full thermodynamic influences of climate change on observed hurricane intensities.
In our system, tools, and pages, “wind speed” always refers to maximum sustained wind speed unless otherwise specified. It does not refer to wind gusts.
In our warming climate, hurricanes bring heavier rainfall and higher storm surge when they make landfall, but our system does not quantify how climate change affects these weather hazards.
While intensified sustained wind speeds can make hurricanes more destructive, our system currently only measures how climate change has influenced storm intensity, not the actual damage caused.
You can find a comprehensive set of reporting resources on hurricanes and climate change in this Climate Matters package from May 2025. All resources are available in both English and Spanish, including this brief one-pager of facts: Extreme Weather Toolkit: Tropical Cyclones.
Also, our RiskViewer site — powered by Climate Central’s FloodVisionⓇ technology — provides photorealistic visualizations of storm surge in coastal locations across 20 states along the Atlantic and Gulf Coasts.