Choose a weather station from the map on the right. This will update the two graphs on the left. The upper one shows 80 years of weather records from that station. The lower one looks at how those weather records are changing over time: Is the recent average different from the historical average? That same comparison is computed for every weather station, and the results are color-coded on the map. (We smooth out the colors by "Kriging" and by sorting the stations into eight equal-size groups).
Weather data is from: Menne, M.J., I. Durre, B. Korzeniewski, S. McNeal, K. Thomas, X. Yin, S. Anthony, R. Ray, R.S. Vose, B.E.Gleason, and T.G. Houston, 2012: Global Historical Climatology Network - Daily (GHCN-Daily), Version 3.22 ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/daily/