Sir, this is a joke about how it would be awful if the sun were always up.
But also, the UK just had its second warmest June ever (England's warmest ever) and was over 30C in many places. During these heatwaves, the temperature rises rapidly, making it uncomfortable because people are not used to the warmer temperatures. After 7 days of warm temperatures, people get used to it.
JFC that's too hot. I'd been thinking maybe Spain would be a nice place to move to and a bit more like where I grew up climate wise... that's way too much like Florida. Is that at least a dry heat or is it outdoor sauna?
Depending where you go. If you go to the coast there's a lot of humidity. On the center the climate is very dry and the nights are not so hot. Typical day in interior spain temperature can go from 10C to 35C easily.
Still pretty hotter than the rest of europe overall.
Climate wise the worst is that we are very vulnerable to climate change. Our highest temperatures are already pretty high so higher temperatures in summer will be deathly. Also some parts of Spain are vulnerable to drastic climate events, recently two hundred people die in a heavy flood in Valencia.
It's an old saying. The Empire had colonies all over the world so at any point in time it was day for at least one colony. Therefore the sun never set on The Empire as a whole.
The joke is making fun of that old saying, pretending it means there is no night for the British isles and all the sun is causing the temperature of the isles to increase.
I hope that's enough explanation to remove any humor from the joke.