Phoenix continues to get warmer, especially in the overnight hours. This is because of the urban heat island effect. What happens is that all the heat we get during the day is retained in all the concrete, steel and glass in the city.
I guess you could think of the concrete as a giant sponge that holds in the heat overnight. We tend to notice it more for our overnight lows and not so much for our daytime high temperatures. We just don't see any more record low temperature set here in Phoenix as a result.
This morning, our overnight low temperature was 86°. The record low temperature on this day was 63° set back in 1918. Phoenix was a completely different place even 30 years ago. Back then we did not have all the buildings or all the concrete.
I really don't think we're going to see any more record low temperatures set here in Phoenix unless we have some type of massive storm in the future. So, I guess humans can have a direct effect on weather when it comes to building our cities and changing the climate around them.
