there was an interesting thing done during that about how the amount of green space reduced temperature by up to 17°F if I recall correctly

Nah, that’s still way off. London is 51.5 degrees north, which would put it well inside Canada. On the west coast that’s about half way between Seattle and the southern border of Alaska, way up the coast of British Columbia past the northern tip of Vancouver island.

It was about ten degrees warmer at sea level at the peak of that heat dome. It was 37C on the mountaintops, about 1800m above sea level