Extremely cold days can be part of global warming, which is why it is now called "climate change" to avoid confusion. It's not that everything gets hotter: while average temperatures rise, the system as a whole gets deregulated, leading to an increase in extreme phenomena, some of which are extremely cold days.
There are also, of course, local patterns that can cause extremely cold days. Averages and quantity also matters, of course. How many extremely cold days for each extremely hot day?
There are also, of course, local patterns that can cause extremely cold days. Averages and quantity also matters, of course. How many extremely cold days for each extremely hot day?