EDIT: I forgot the fact that CH4 is being burned, not released as-is in the atmosphere. Original comment: Carbon footprint is just one way of measuring the im

EDIT: I forgot the fact that CH4 is being burned, not released as-is in the atmosphere. Original comment: Carbon footprint is just one way of measuring the impact on climate, but that's only because CO2 is the biggest pollutant. However, methane (CH4) is much much much better in trapping heat. 19 times more potent over a 5 year period, or 4 times more over a 100 year period (source: http://www.onegreenplanet.org/animalsandnature/methane-vs-carbon-dioxide-a-greenhouse-gas-showdown/ http://www.onegreenplanet.org/animalsandnature/methane-vs-ca...). This is despite having the same number of carbon. So technically the "carbon footprint" is zero if, as Elon said, you're extracting carbon from CO2 in the atmosphere, but if you change it to CH4, you're worsening by a big factor the impact on climate. Maybe over thousands of years that factor goes down to 1x but still... All this is assuming you extract CH4 from atmosphere, which is extremely unlikely for economical reasons, as others have pointed out.