I've heard a good number of folks lately saying they remember it being colder when they were young, with wind chills in the -50s, -60s and even the -70s. It is true that our wind chill values used to get that cold and won't any longer. It's not because of global warming. It's because the wind chill formula was changed.
In 2001, the National Weather Service published a new wind chill chart. The new formula that is used to calculate the wind chill uses advances in science, technology, and computer modeling.
The old formula used to use a "calm" wind speed of 4 MPH. The new formula uses 3 MPH. The biggest change is the height above the ground where the wind is measured. In the old formula, the wind speed was measured at 33 feet above the ground, where the anemometer was located. The new wind chill formula uses the wind speed at 5 feet, the average height of an adult human's face. There is a huge difference in wind speed at 5 feet above the ground versus 33 feet.
For example, with a temperature of -10° F and a wind speed of 35 MPH the wind chill is -41° F. Using the old formula and the same conditions, the "old" wind chill would be -67° F. The conditions are the same, but what is different in the height the wind is measured and the effects on the skin.
That being said, wind chills in the -30s and -40s now are just as dangerous as the wind chills of the -60s and -70s of the past.
For more information about wind chill, the National Weather Service has some more information: National Weather Service Wind Chill Index