There is a press release about the United States Historical Climatology Network's (USHCN) measuring devices and their improper placement for measuring temperature. It appears that about 90% of the measuring devices are in urban or heat-sink areas. Their placement by concrete and asphalt that radiate heat or placement near air conditioning or machinery that kick out hot exhaust has inflated the numbers recorded.
Now when someone points to the data you can tell them it is wrong.
Go read the press release for the full story.