Are Historical Emissions Harmful? Part II

I said I would give three reasons why the question of the harmfulness of past emissions isn't that easy as it seems at first. Here's a second (and trivial) reason:

Past industrialisation not only caused damages to the environment but it also had huge benefits. First of all it had benefits for the people who lived in the past, but secondly it also has indirect benefits for ourselves and future generations. When we talk about the harmfulness of past emissions it is unclear whether we mean:

• Only the damages caused by past emissions. Or whether we mean
  
  
• The Net Damages caused by past emissions, i.e. the benefits of the activities which caused the emissions minus the damages caused by these emissions.
  Note that the Net Damages of past emissions might easily be negative, i.e. the industrial activities of the past might well have a positive net effect on human wellbeing, possibly even a positive net effect on the wellbeing of the present generation.