Frequent tornadoes and thunderstorms that kill people and destroy property have become a matter of grave concern. In the United States alone, the insured losses caused by severe thunderstorms have been put at $8.5 billion from the period between January to June 2016.

A new study has tried a linkage between climate change and the increasing incidents of tornadoes. Calling for a deeper study on some meteorological factors, the paper zeroes in on vertical wind shear as an important variable in triggering mega storms.

Led by Michael Tippett, associate professor of applied physics at Columbia Engineering, the study published in Science scans significant tornadoes and outbreaks lasting for many days. It notes that major tornado incidents had been going up substantially since 1954 though a definite reason could not be given for that.

In the paper, researchers have analyzed the trends in the tornado outbreaks and found extreme outbreaks are increasing at the fastest rate.

"This study raises new questions about what climate change will do to severe thunderstorms and what is responsible for recent trends," says Tippett, who is also associated with the Data Science Institute and the Columbia Initiative on Extreme Weather and Climate.

Offering new insight into the trends in environmental conditions that encourage thunderstorms and tornadoes, the study looks at the convective available potential energy, or CAPE, and storm relative helicity, a measure of vertical wind shear.

With greenhouse gases trapping more energy and heat in the atmosphere air will start holding more water and that opens the scope for extreme storms.

One crucial ingredient in forming violent storms is vertical wind shear, which lifts intensity in sync with altitude. Unlike CAPE, shear does not change much with global warming.

Tornado Alley

The study notes that an increasing number of people are killed in tornado outbreaks, or sequences of six or more tornadoes occurring in close succession. Such twisters had been responsible for 79 percent of tornado deaths from 1972 to 2010.

In fact, there is scare among citizens of "tornado alley" in America's Midwest as outbreaks in the United States are turning more extreme.

Tornado Outbreaks Up

Climate scientists suspect warming temperatures as the triggers of tornadoes, as warm and wet conditions drive the tornado pump.

However, Tippett is yet to see a direct correlation between climate change and bigger outbreaks.

"It's not the expected signature of climate change," he says, but adds that "it could be either something else, or we really don't understand what climate change is doing."

There are many factors influencing weather, including the circulation of warm water in the Pacific and Atlantic oceans. That circulation pattern may change over decades and alter long-term weather patterns.

Tippett says ocean changes might have a role in tornadoes though there is no hard evidence.

The concern over tornadoes is genuine as outbreaks are hurting people and insurance industry is also hard-pressed to provide cover, with bigger outbreaks forcing massive payouts.