Dear authors, I decided, that your work still needs major work to be publishable on ACP. My main concern ist the analytical model you introduce. As the reviewers I do not understand why you insist on keeping it in the publication. Especially if it is rather simple and faulty. I can also not see, why you need it to motivate the numerical experiments. The argument, that a substancial amount of CH4 is transported into the Arctic/Antarctic and across the globe would be motivation enough. Also, as one reveiwer said, your statements around line 80 do not need a model to be rather clear.

In your review you write: 'We hope this paper will dissuade future studies from using this
metric for the purpose of isolating Arctic emissions.' But such a statement does not appear in your manuscript. As I read your manuscript, more work needs to be done to develop an improved IPD. There seems to be a large discrepancy between your intentions and your manuscript.