We also have to be careful when making such assessments. The semiconductor industry was once viewed as clean, and maybe it was clean compared to older industries. Yet that perception came from appearances rather than fact since the pollution was either invisible (e.g. hazardous chemicals leeching into the ground, verses belching smokestacks) or out of sight (e.g. rare earths are often extracted in foreign nations). In order to figure out how much of an environmental impact something has, we need to collect data and do an analysis rather than depending upon what we can see and touch.

Even then, reliable data and analysis may produce differing conclusions based upon shifting priorities. Today's discussions are tied to greenhouse gasses. In prior decades, environmental discussions were tied to: deforestation and habitat loss, groundwater pollution, air pollution with respect to public health and acid rain, the ozone hole, etc..

Even if we could agree on priorities, it is difficult to assess the true impact because technological change brings about behavioural change. The automobile may be cleaner than the horse and buggy. On the other hand, more people walked or used mass transit before the automobile. Streaming a movie may be cleaner than watching a DVD, but is it cleaner when each member of a household is viewing a different movie on a portable device in contrast to watching a broadcast together on the family TV.