On a global average, the amount of mercury falling out of the sky has tripled since the Industrial Revolution, primarily because of the burning of fossil fuels. Although this atmospheric deposition has long been considered the key vector for the widespread contamination of freshwater and coastal ecosystems, some scientists are focusing on another potential source: subterranean flows of terrestrial groundwater.

"A group of chemicals called hydrofluorocarbons, long hailed as a substitute for gases that can destroy the ozone layer, are now seen as a growing greenhouse threat given their outsize ability to warm the atmosphere."

Tesla Motors' chief executive, whose company has been mired in legal actions, predicted in a blog post that the company would become profitable next month.

Two brothers are busting levees to return the Ouachita National Wildlife Refuge to its primeval condition.