NYT: 4th of July Kills the Planet

...Charcoal is made of wood, so the carbon it releases upon combustion is approximately equal to the carbon the tree it came from once removed from the atmosphere. In theory, charcoal should be less damaging than propane, which releases carbon that has been sequestered harmlessly underground for hundreds of millions of years.

It's far more complicated in practice, though. We get most lump charcoal from cutting down mesquite trees, and in addition to the deforestation effect, it takes more fuel to produce and transport charcoal than it does propane. As a result, according to a 2009 study in the journal Environmental Impact Assessment Review, propane is nearly three times as efficient as lump charcoal.

Charcoal briquettes, however, are a different story. The compressed round briquettes are made from scrap wood that would otherwise go to waste. The better manufacturers build their plants near construction centers and use recycled heat from those centers to power their briquette kilns. If you take that into account, charcoal briquettes are ahead of lump charcoal and propane as the best option in terms of climate change. (Any kind of charcoal, however, releases more particulate matter than propane, which makes charcoal a greater contributor to air pollution. There are few easy choices in environmental analysis.)