There are four baseline observatories:

1. Point Barrow, Alaska - The principal employer of this town are the North Slope oil fields, which supply natural gas for heating, and fuel for snowmobiles and other vehicles in the area. According to this website the population of Barrow has increased by 4.8-fold since 1950. The obseratory is located just 8 km east of this town.

2. Mauna Loa, Hawaii - This is an active volcano. The observatory is located on the northern flank of the volcano and "is the site where the ever-increasing concentrations of global atmospheric carbon dioxide were determined".

3. American Samoa - This consists of five volcanic islands (dormant?). The population of 58,000 people are supported mainly by the tuna fisheries and tuna canneries. Pago Pago has one of the best natural deepwater harbors in the South Pacific Ocean, sheltered by shape from rough seas and protected by peripheral mountains from high winds; American Samoa is a strategic location in the South Pacific Ocean. As such its economy is strongly linked to the United States. Imports include 7 percent petroleum products. The observatory is run year-round by 3 staff that commute to work, and obtains 70 percent of its power from non-renewables.

4. South Pole - The observatory location might be pristine, but with a very unusual climate.

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Overall, the trend is for increasing atmospheric CO2 regardless of the location of the observatory, with location only affecting the magnitude of seasonal varation, with the long-term trend the same gradual increase. But the graph is skewed: if the vertical axis started at zero instead of 320 ppm, the trend might not even be visible. Furthermore, the data only goes back 30 years and there may be longer natural cycles to account for the trend, and if the above info might suggest, the activity of local populations might account for it too. In addition, the are huge cycles with both increases and decreases of atmospheric CO2 going back tens of millennia. In addition to human activity, both local and large-scale, how much of the current trend could also be partially accounted for by Milankovich cycles, variations in solar output, increased or decreased volcanic activity, biological effects in the oceans and the air, dust or cometary clouds between the Earth and Sun, purturbations of Earth's perihelion/aphelion by Mars or Venus, etc.

The partial effects of these phenomena haven't been included in the data as presented.