Could Global Warming Change Tornado Season?

With the planet heating up, many scientists seem fairly certain some weather elements like hurricanes and droughts will worsen. But tornadoes have them stumped.

As the traditional tornado season nears, scientists have been pondering a simple question: Will there be more or fewer twisters as global warming increases?

There is no easy answer, and scientists are unsure if climate change has played a role in recent erratic patterns.

In 2011, the United States saw its second-deadliest tornado season in history: Nearly 1,700 tornadoes killed 553 people. The May 2011 Joplin, Mo., twister was the single deadliest in American history, killing 158 people and causing $2.8 billion in damage.

In 2012, tornado season was earlier and busier. Through April there were twice as many tornadoes as normal. Then the twisters suddenly disappeared.

Public opinion polls show Americans blame global warming for bad tornado outbreaks, but climate scientists say that’s not quite right. One reason they can’t figure out how global warming might affect tornadoes is that twisters are usually small weather events that aren’t easily simulated in large computer models.

Scientists are looking at two main factors in producing tornadoes: moist energy in the atmosphere and wind shear. The atmosphere can hold more moisture as it warms, and it will likely be more unstable, creating more moist energy. Harold Brooks, with the National Weather Center, and Stanford University scientist Noah Diffenbaugh think warming will create less wind shear. That would suggest fewer tornadoes. But if there’s more moist energy, that could lead to more tornadoes. Diffenbaugh says recent computer simulations show the moist energy may overcome the reduced shear and produce at least more severe thunderstorms, if not tornadoes.