Changing Baselines
When coal was first being burned in industrial revolution era London, many people complained about the decreased air quality. However, as the generations passed the complaints stopped and the pollution was seen as normal. This is the problem of changing baselines. Those Londoners who had known of preindustrial air quality were upset to see the degradation of their air. But in later generations, people had never experienced clean air in London and did not think there was anything wrong with the pollution.