US tornadoes: Is climate change to blame?
Several US states have been hit by a devastating series of tornadoes, with an expected death toll of more than 100.
These are extremely rare outside the spring and summer, in the US, but this December there has been a record number of tornado warnings.
So is climate change causing more frequent and stronger tornadoes?
How are tornadoes formed?
When warm moist air is trapped by cooler air, it causes thunder clouds to form.
The warm air rises, creating an updraft.
And if there are also strong winds moving in...