Factor in the "urban heat island" effect as part of the ride in global temperatures. Temperature stations that used to be rural are now in urban and suburban settings. Do you realize that one of the most common places for temperature stations is at airports? Used to be that we actually had valid reasons to monitor meteorological/climatic conditions. Monitoring immediate and longterm trends at airports seemed only natural for safe operation from day to day, year to year. What has happened to airflight after WWII? What typically happens around an airport that once was a landing field on the outskirts of town? You got it - commerce. Urbanization.
So what do you do now? How can you relocate a station to an area that does not reflect falsely increased temperatures, but still retain continuity with previous direct measurements? Short answer: you can't. But instead of modelers telling you that they may be wrong seeing how they had to make a best guess adjustment, they just give you their findings, tell you that everyone agrees, and accept it on "good faith." Right.
Either way, research is being done on the use of lighter colored aggregates in road use, although it's mostly from the angle of increased visibility. Understand that the lighter colors would lead to increased glare, driver fatigue from the increased light, and possibly decreased ability to retain the warmth necessary to keep roads clear of snow and ice.