Is Your City Getting Hotter?

I had an idea for how to very simply visualize temperature changes for a given location...

Interpretation

To read that, simply interpret 'dark' as 'colder' and 'orange' as 'hotter'. Looking at the Mexico City plot for example, you get a clear trend towards warmer temperatures in the last 50 years than in the 50 years before that. I ran this for a number of cities, and the results are below...

That's it. Pretty simple way to see a temperature trend.

Data

I used data from the CRU TS dataset. I simply averaged January 1911, January 1912, etc. to get a January normal, did this for each month, then subtracted it from each month/year combination to see if that month/year combination was hotter or colder than the average. The total range here is 1911 to 2016.