A friend of mine is working on a small project to map receding North Pole summer sea ice minimums by decadal averages on a wall-paper map.
Unfortunately, it seems as though the map projection for his wall-paper map is non-standard (or closely related to the Robinson projection, but not exactly).
The map in question can be found here: http://www.pinboardking.com/product/big-red-grey-worldmap/
Due to the fact that the sea ice min/max vectors in the North are very sensitive to projection warping/aberration, I'm trying to find the exact EPSG to be as accurate as possible.
How can the projection be identified or approximated?
Edit: Uploading a picture of said map that I had on hand for better reference.