That indicates a significant percentage increase in CO2 near a volcano. Has anyone accurately measured the heat retention properties of either value? Do we know how? It would be nice to have a curve relating ppm of the earth average CO2 to the heat retention properties of the atmosphere. This is probably more subtle than plotting average temperature of the atmosphere and/or oceans against the ppm of CO2.

Wouldn't you expect CO2 readings taken near a volcano to introduce a less accurate indication of the earth average increase in CO2 than would ten thousand or so readings from all around the earth? My suspicion is that even 1000 ppm CO2 would be below the threshold at which significant heat retention occurs. At 1000 ppm the biota will swing into action to counterbalance the effect.

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?