It's not climate change. All the cities are way hotter than the surrounding forests because they're made from steel, glass, concrete, and asphalt, which soak up ambient heat like a sponge and slowly release it over the day. Additionally, the lack of plant life to help cool the air by respiring water brought up from underground means the temperature goes up and up and up. Not all the heat manages to escape which increases the average temperature. Repeat this process over the years and it looks like it's way hotter than it should be. Go to some national park in France and surprise! the climate history suggests no climate change is happening at all.

You can test this by sitting on some hot asphalt road and compare it to sitting in the field of grass and then comparing that to sitting in a forest. Guarantee you'll be sweating on that road in a few minutes.

In the UK, it just so happens that they cut down the majority of their forests, urbanized the place, and people just keep wanting to immigrate there. This ain't the middle of the Rockies where no one lives.