I can't believe I've been wasting my time with electric cars and solar. To do my part for climate change, I should move to an empty desert and install propane fired everything. Because my actions don't matter, the relative population density of my area does. The fact that my state or country, housed within manmade imaginary lines, has an outsized area of uninhabitable land should definitely dilute my personal GHG impact. Hey, Greenland looks good. Population density 0.03 people per square kilometer. No wonder it's called Greenland!
It has opened my eyes to a number of other things as well. We should look at the number of cheesecakes eaten per square centimeter of a nation to compare health statistics. Doesn't matter how many people live there, low population nations should be rewarded for their lower cheesecake eating habits.
If you want to remove the personal incentive structure from living, breathing human beings, measure GHG output per square mile. Population density is tremendously abstracted from our control and dependent on myriads of other factors - education, climate, elevation, natural resources, etc. If you want to actually have a metric by which to reasonably measure the outcome of climate change policy, measure per capita. This is not to say that you ignore population growth as an overall factor in resource use, but implying that somehow population size is a result of good national climate policy is entirely specious.