Coal, like oil, represents the organic remains of ancient photosynthesis. Oil is primarily the residue of marine algae trapped in ocean sediment, whereas coal originated from land plants buried under soil. During photosynthesis, plants reduce atmospheric carbon-dioxide (CO2) to produce glucose, the basis of all complex organic molecules in plants and animals.

In most cases, when organisms die, bacteria oxidize the carbon molecules back to CO2. In exceptional cases, in low-oxygen environments, the molecules remain preserved as hydrocarbons with the solar energy locked inside. When we burn coal, oil, or gas, we release ancient solar energy. We get warm, cook food, make steel, and race automobiles, with ancient sunlight.

However, when we burn coal and oil, we also release the carbon back into the atmosphere. And there, as we now know, lies the rub.