The U.S. saw powerful tornadoes sweep through parts of the middle of the country in 2021 with the violent winds particularly destructive.

In 2020, there were 1,050 tornadoes that killed 78 people and caused $4.4 billion in damage. In 2021, there were 1,256 tornadoes and 104 deaths with unspecified damage that is expected to reach $5 billion.

Much of the death toll came from December's deadliest on-record tornado, which wept through portions of the South and Ohio Valley that saw harsh damage in Western Kentucky.

Tornadoes hit all parts of the world in 2021, including Indonesia, Canada, Australia, Russia, and the Czech Republic.

Tornadoes form when a thunderstorm has a particular combination of winds and are usually accompanied by different severe weather patterns such as strong winds and hail.

The effects of climate change may not have a direct relationship with tornadoes. In a report on Dec. 13, National Geographic pointed out that "unlike heat waves and floods, the link between a warming world and tornadoes is complicated and inconclusive."

But climate change may have a strong indirect impact.

"Climate change may be involved in some noteworthy recent shifts in the location and seasonal timing of the tornado threat," Colorado-based meteorologist and journalist Bob Henson wrote in July for Yale Climate Connections.

Henson cited a 2016 study that found "an increasing number of each year’s tornadoes are occurring in outbreaks," which are classified as a period "of one to several days with at least six closely spaced EF1+ tornadoes."

In a New York Times report on Dec. 15, tornado expert James B. Eisner noted that "What is causing these changes in tornado behavior is still unclear, but global warming is probably playing a role through changes to the environments that support supercell clusters."