Well, I don;'t think that the indirect effects are being much included at all. For example, the United Nations' Green Revolution was responsible for keeping perhaps a billion people from dying of starvation. They and their descendants now are causing a fair fraction of that "damage".
Are the US and other First World nations wholly responsible for correcting this damage as well as their direct effects, or in this case would it be appropriate to expect those whose lives were saved to contribute a portion of t\heir own upkeep, so to speak?