John Cook loves to quote the statistic that “there are more record highs than record lows” in recent years.
Well surprise, surprise surprise. Study after study has shown that urbanization keeps nighttime temperatures up. This has been understood for hundreds of years. Even in the tiny town of Barrow, Alaska – UHI keeps winter temperatures 2.2C above the surrounding regions.
During winter (December 2001–March 2002), the urban area averaged 2.2 °C warmer than the hinterland. The strength of the UHI increased as the wind velocity decreased, reaching an average value of 3.2 °C under calm (<2 m s?1) conditions and maximum single-day magnitude of6 °C
http://www.cas.umt.edu/geography/documents/Hinkel_etal_2003_winter_UHI.pdf
Phoenix has 4-7C nighttime warming
The average minimum May temperature at the urban locations displayed an apparent upward increase through the time series (1910 through 2000), which was attributed to the urban growth of the region. By the end of the series, there was a +4 to 7 ºC (7 to 13 ºF) difference between the urban minimum temperatures and the rural minimum temperatures
National Weather Service – NWS Phoenix
Of course there are fewer record lows, and the reasons are well understood. No need for alarmists to lie about it.