Globally, the generation of the electricity that powers modern society is still heavily reliant on a fuel that's been used for thousands of years: coal. Coal has two virtues: it's plentiful and extracting it is cheap. But almost every step involved in its production and use brings problems.

Extracting it is hazardous to miners, while alternatives like open-pit mines or mountain top removal permanently alter the landscape and often release hazardous chemicals into the environment. Burning it requires careful pollution controls to avoid the release of hazardous chemicals like mercury or acid-forming sulfur compounds. It also releases the most carbon dioxide per unit of electricity generated. Combustion also leaves behind a toxic sludge that creates a long-term contamination hazard.

The April issue of National Geographic includes an article that asks "Can coal ever be clean?" (The answer is no, but at the right cost, it could be cleaner.) The article is accompanied by the photographs of Robb Kendrick, who has captured some of the costs of coal at sites around the world. National Geographic got in touch and offered to share some of these images with our readers; you can find these and more at the magazine's website.