A record-breaking tornado storm caused destruction in USA, killing hundreds of people and destroying infrastructure.
Tornadoes are common in US during spring-time but occur rarely in December. The event was fuelled by La Nina weather pattern and moist weather.
If confirmed that the twister was singular one, it will break a 100-year old record for how long a tornado stayed on the ground in a path of destruction.
Atmospheric conditions that create tornadoes are intensifying in recent times, which may be as a result of climate change.
Causes of tornado
Tornadoes are swirling vertical air-columns made of thunderstorms. They stretch from clouds to the ground and move along a path, destroying everything that comes in between.
Thunderstorm occur through a condition known as atmospheric instability in which denser, drier cold air is pushed over warmer, humid air.
A condition known as updraft will start occurring when winds vary in speed or direction at different altitudes.
The wind changes allow the spin necessary for a tornado. Changes in wind’s speed and direction are needed for strong tornadoes.
They usually do not occur in winters because of big difference in temperature and air pressure. This time the situation was different.
The warm, moist air in mid-west helps formation of tornadoes. This time around, La Nina conditions created warmer conditions.
Thunderstorms updraft needs to be sustained for tornado to strengthen. Usually they lose energy in a matter of minutes but in this case it sustained for hours.
Climate change and tornado outbreaks
The La Nina event may have been responsible for this storm but scientists say that warm conditions in December may become norm in future as planet starts warming.
However, every thunderstorm event cannot be attributed to climate change as only 10% of thunderstorms lead to tornadoes.
Long-term estimates say that US may see more tornadoes occurring in December, which earlier was not the case.
The tornado area has shifted eastwards in recent times due to increasing temperature and air moisture. People living in Mississippi River Valley and Ohio River Valley are becoming increasingly vulnerable.