I've tried running the numbers, but actually finding numbers is hard here.
If I'm understanding the sources correctly, the coal seam on fire in Centralia is about 3700 acres in total size, and coal seams seem to be only a few feet thick generally. Plugging in 8 feet for a thickness (which I think includes a large amount of non-coal rock, but I don't know the recoverable fraction so I'll estimate 100% of it to be coal), I get that the total CO2 production of burning all of it would be about 7 million metric tonnes of CO2. That would be for the entire lifetime of the fire.
So one coal seam fire would produce about 0.2% of the US's yearly CO2 emissions. Keeping in mind that these fires last for decades, that would suggest that coal seem fires account for less than 1% and probably less than 0.1% of CO2 emissions.
If I'm understanding the sources correctly, the coal seam on fire in Centralia is about 3700 acres in total size, and coal seams seem to be only a few feet thick generally. Plugging in 8 feet for a thickness (which I think includes a large amount of non-coal rock, but I don't know the recoverable fraction so I'll estimate 100% of it to be coal), I get that the total CO2 production of burning all of it would be about 7 million metric tonnes of CO2. That would be for the entire lifetime of the fire.
So one coal seam fire would produce about 0.2% of the US's yearly CO2 emissions. Keeping in mind that these fires last for decades, that would suggest that coal seem fires account for less than 1% and probably less than 0.1% of CO2 emissions.