Tornadoes and Climate Change

Photo courtesy NOAA

Tornadoes and Climate Change

Definition of a Tornado

Tornadoes are formed by a combination of atmospheric instability and wind shear. Instability occurs when warm, moist air is wedged under drier, cooler air aloft. This warm air rises, causing the intense updrafts and downdrafts seen in strong thunderstorms — the incubators of tornadoes. Wind shear refers to changes in wind direction and speed at different elevations in the atmosphere. The combination of instability and wind shear forms the rotating column of air that we associate with a tornado. Tornadoes that form over water are known as waterspouts.

The link between tornadoes and climate change is currently unclear. One problem is the difficulty in identifying long-term trends in tornado records, which only date back to 1950 in the United States. Also, the population in many areas affected by tornadoes has grown, so it’s possible that tornadoes in the early part of the 20th century occurred without anyone seeing them. Improved technology, such as advanced radar, also helps us “see” tornadoes that may not have been detected decades ago.

Another problem lies with the physics associated with tornadoes. Researchers are working to better understand how the building blocks for tornadoes -- atmospheric instability and wind shear -- will respond to global warming. It is likely that a warmer, moister world would allow for more frequent instability. However, it is also likely that a warmer world would lessen chances for wind shear. Recent trends for these quantities in the Midwest during the spring are inconclusive. Climate change also could shift the timing of tornadoes or the regions that are most likely to be hit, with less of an impact on the total number of tornadoes.

Adding to the difficulty, tornadoes are too geographically small to be well simulated by climate models. Models can simulate some of the conditions that contribute to forming severe thunderstorms that often spawn tornadoes. Multiple studies (see here and here) find the conditions that produce the most severe thunderstorms are likely to occur more often in a warmer world, even if the total number of thunderstorms decreases (because of fewer weak storms). However, this work does not conclusively tell us whether tornadoes should follow the same trend as their parent thunderstorms.

Threats posed by tornadoes

The most significant threats from tornadoes are the dangers posed by strong winds and debris that is caught up in those winds. Although individual tornadoes may affect a relatively small area compared to large tropical storms, they can threaten people, homes, and communities.

NOAA estimates that, on average, about 1,200 tornadoes occur across the country annually, but several hundred more or fewer tornadoes can occur in any given year.

On average, tornadoes in the United States cause 70 deaths and 1,500 injuries per year. The death toll from tornadoes has dropped rapidly because forecasters have more tools to detect dangerous weather and quickly warn people to take shelter.

However, tornadoes still cause billions of dollars a year in property damage. The costliest year on record for tornado damage was 2011, when seven tornado and severe weather outbreaks each caused more than $1 billion in damages, and the total damage for the year was more than $28 billion.

How to Build Resilience

Communities can bolster their resilience and reduce the impacts from tornadoes by:

  • Adopting more stringent building codes in tornado-prone areas
  • Continuing to support new severe weather research and improvements to forecasts for severe weather
  • Heeding watches and warnings when they are issued, and ensuring that individuals can be reached  by emergency alert systems (for example, through text message, television, and radio, or via tornado sirens)

To Learn More

NOAA Severe Weather 101: Tornadoes

NOAA’s Storm Prediction Center FAQ for Tornadoes

Ready.gov’s Resource Page for Tornadoes

Federal Emergency Management Agency: Taking Shelter From the Storm: Building a Safe Room for Your Home or Small Business