There is also good reason to believe U.S. temperatures have not warmed at all since the 1930s. Raw temperature readings at the preexisting stations indicate temperatures are the same now as 80 years ago. All of the asserted U.S. warming since 1930 is the product of the controversial adjustments made to the raw data. Skeptics point out that as the American population has grown, so has the artificial warming signal generated by growing cities, more asphalt, more automobiles, and more machinery.