Hurricanes and Climate Change: What the Science Says

Hurricanes are among the most destructive weather events on Earth. After a major storm, people often ask whether climate change is to blame. The honest answer is nuanced: scientists are confident about some links, less certain about others, and careful not to overstate what the data show. This explainer walks through how hurricanes work and what the evidence says.

Hurricane, typhoon or cyclone?

These are all the same type of storm: a tropical cyclone. The name depends on where it forms. In the North Atlantic and the eastern and central North Pacific, strong tropical cyclones are called hurricanes. In the western North Pacific they are called typhoons, and in the Indian Ocean and South Pacific they are usually called cyclones or severe tropical cyclones.

How hurricanes form

A hurricane is essentially a giant heat engine. It needs several ingredients to come together:

1. Warm ocean water. Sea surface temperatures of at least about 26 °C (79 °F), extending to some depth, provide the heat and moisture that fuel the storm.
2. Moist air. Humid air in the middle levels of the atmosphere helps thunderstorms keep growing.
3. Low wind shear. Wind shear is a change in wind speed or direction with height. Strong shear tears developing storms apart.
4. A starting disturbance. Many Atlantic hurricanes begin as clusters of thunderstorms moving off West Africa.
5. Distance from the equator. Earth's rotation, through the Coriolis effect, makes the storm spin. That effect is too weak very close to the equator.

As warm, moist air rises, the water vapor condenses into clouds and releases heat, which makes the air rise faster and lowers pressure at the surface. More air rushes in to replace it, picking up more heat and moisture from the ocean. When sustained winds reach 74 miles per hour (119 kilometers per hour), the storm becomes a hurricane.

The National Hurricane Center rates Atlantic and eastern Pacific hurricanes on the Saffir-Simpson scale from Category 1 to Category 5, based on sustained wind speed. Category 3 and above, with winds of 111 mph or more, are called major hurricanes.

Why the climate question is hard

Studying long-term hurricane trends is difficult for a few reasons:

• Short reliable records. Before satellites, storms that never hit land could be missed or poorly measured. Consistent global satellite monitoring only goes back to the 1970s and 1980s.
• Big natural swings. Hurricane activity varies a lot from year to year and decade to decade, affected by patterns such as El Niño and La Niña and long-term cycles in the Atlantic.
• Relatively few storms. Only around 80 to 90 tropical storms form worldwide in a typical year, so trends in rare, extreme storms take a long time to emerge from the noise.

Scientists therefore combine observations with physical understanding and computer models. Here is what that combined evidence says, drawing mainly on the IPCC's Sixth Assessment Report and NOAA's Geophysical Fluid Dynamics Laboratory.

What the science says

Aspect	What is expected with warming	Confidence
Rainfall	Heavier rain rates near the storm center	High
Storm surge flooding	Worse, because surges start from higher sea levels	High
Peak intensity	A larger share of storms reach Category 4 and 5	Medium to high
Rapid intensification	May become more common	Medium, still being studied
Total number of storms	Similar or fewer worldwide	Medium to low
Forward speed and tracks	Possible slowing and shifts toward the poles in some regions	Low to medium

Rainfall

This is one of the most confident findings. Warmer air holds more water vapor, about 7 percent more for each degree Celsius of warming. Hurricanes gather that moisture and wring it out as rain. Studies of individual storms, such as Hurricane Harvey's extreme rainfall over Texas in 2017, have concluded that climate change increased the total rainfall. Inland flooding from rain is already one of the deadliest hurricane hazards in the United States.

Storm surge

Storm surge is the rise in seawater pushed ashore by a storm's winds. Even if storms themselves did not change at all, higher sea levels mean every surge reaches farther inland. Global sea level has risen by roughly 20 centimeters (about 8 inches) since 1900, and more in some places. Read more in Why sea levels are rising.

Intensity

Warmer oceans raise the theoretical maximum intensity a hurricane can reach. The IPCC concluded that the proportion of major tropical cyclones (Category 3 to 5) has likely increased globally over the past four decades and that the proportion of very intense storms is projected to rise further with more warming. That does not mean every storm will be stronger, but the odds shift toward the most dangerous ones.

Rapid intensification

Rapid intensification is when a storm's winds jump by at least 35 mph within 24 hours. It is especially dangerous because it can leave little time to prepare. Several recent studies suggest it has become more common in the Atlantic, and a warming ocean makes it physically more likely, but scientists are still working to separate the climate signal from natural variability.

Frequency

Perhaps surprisingly, the evidence does not point to more hurricanes overall. Many models project that the total number of tropical cyclones worldwide will stay about the same or decrease, even as the strongest storms become a larger share. Some individual basins may see increases, and this remains an area of ongoing research.

What this means for people

For anyone living near the coast or in hurricane-prone inland areas, the practical message is that both water and wind deserve attention. Historically, water from storm surge and inland flooding has caused the majority of US hurricane deaths. Following official forecasts and evacuation orders, knowing your evacuation zone, and planning for flooding as well as wind all save lives. The National Hurricane Center provides forecasts, storm surge maps and preparedness guidance.

The bottom line

Climate change is not making every hurricane stronger, and it may not be increasing their total number. But scientists are confident it is making hurricane rainfall heavier and storm surge more damaging, and the evidence points to a growing share of the most intense storms. Those are the changes that matter most for the damage hurricanes cause. To understand the extra heat behind these trends, see What is the greenhouse effect?