The European Union is on a continent-wide push to reduce its carbon emissions. But some environmentalists say this goal is threatened by a nearly 30-year-old treaty enacted in response to the fall of the Soviet Union.

On this episode of our weekly podcast, Parts Per Billion, we hear from Stephen Gardner, Bloomberg Law's Brussels correspondent. He explains how a treaty meant to spur energy investment in post-Soviet republics has turned into a powerful tool of Europe's fossil fuel industry.