Global Warming Increases Severe Thunderstorms: Tornades, Hail and Damaging Winds

Global warming is causing sea levels to rise and ice to melt, but it may also be impacting our weather. It turns out that the changing climate could be causing severe thunderstorms to increase, which could mean billions of dollars-worth of damages in the future.

Severe thunderstorms are one of the primary causes of catastrophic losses in the United States. Often including heavy rainfall, damaging winds, hail and tornadoes, thunderstorms can quickly turn into disasters. In 2012, 11 weather disasters in the U.S. crossed the billion-dollar threshold in economic losses.

In order to examine how warming might affect atmospheric conditions, researchers turned to a complex ensemble of physics-based climate models. They then identified two main ingredients when it comes to generating a thunderstorm. The first is that the atmosphere must contain a significant amount of what scientists call convective available potential energy (CAPE), created as the air in the low atmosphere warms. The second component involves CAPE interacting with strong vertical wind shear--essentially a moving wind current that organizes the atmospheric energy and moisture such that it can sustain a storm.

The new model indicates an overall decrease in the amount of wind shear, yet the bulk of that decrease occurs on days that produce levels of CAPE that are much lower than is normally seen during severe storms. The net effect is that the increases in CAPE on other days drive increases in the occurrence of severe thunderstorm environments.

In fact, the researchers found that the biggest changes with global warming occurred in the spring season. At that time, the U.S. would experience about two-and-a-half addition storm days by the late 21^st century.

"We're seeing that global warming produces more days with high CAPE and sufficient shear to form severe thunderstorms," said Noah Diffenbaugh, one of the researchers, in a news release.

That's not all they found. The researchers also discovered that sustained warming is likely to cause robust increases in storm days over large areas of the eastern U.S. not only in spring, but also in winter and autumn. The summer season also showed increases over the region as a whole.

"The severe thunderstorms we experience now can result in very high economic losses," said Diffenbaugh. "Sadly, we have many examples of cases where a single storm has had disastrous impact. So a 25 to 30 percent increase in the annual occurrence represents a substantial increase in the overall risk."

The findings reveal the importance of understanding how global warming will impact our climate. More specifically, it could allow officials to better prepare for the increase of thunderstorms in the future, which could help mitigate economic losses.

The findings are published in the journal Proceedings of the National Academy of Sciences.