The EPA pulled off the feat by sharply increasing the amount of oxygen-poor exhaust that is recirculated into the combustion chamber and increasing the pressure of the fuel being forced into the cylinder.

FORBES: EPA, Inc.

Two other techniques, called gasification and oxy-combustion, work by reacting coal with pure oxygen rather than air, and thus produce exhausts that require little treatment before burial.

ECONOMIST: Carbon capture and storage

These devices, which work by combining hydrogen with oxygen from the air to produce electricity, are popular candidates to replace internal-combustion engines in road vehicles.

ECONOMIST: The dawn of micropower