If the world is to tackle the problem of climate change in earnest, "clean coal" has to become more than just an amusing oxymoron. All fossil fuels contain carbon, but coal is by far the most carbon-intensive. This is troubling, since global warming seems to be driven by an increase in the level of atmospheric greenhouse gases, of which carbon dioxide (CO_2) is the most worrisome. Coal is also the most abundant fossil fuel (see chart on next page). If all known conventional oil and gas reserves (those in underground formations, obtained by drilling) were burned, the level of CO_2 in the atmosphere would still be less than twice what it was before the beginning of the industrial revolution. Climate change associated with that level of CO_2 might be tolerable. Burn all the coal, however, and it would be more than four times that starting-point-with larger, less predictable and quite likely more unpleasant climatic consequences.
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