The ozone hole is both an environmental success story and an enduring global threat

• The headlines in recent months read like an international eco-thriller.

At Mauna Loa Observatory, perched high on a Hawaiian volcano, researchers measure unusual levels of CFC-11 in the atmosphere.

• Authors:
• The Conversation

The measurements baffle the scientific community: CFC-11, a potent ozone-depleting gas, has been carefully monitored since it was banned under the 1987 Montreal Protocol.

But the measurements are soon confirmed by observing stations in Greenland, American Samoa and Antarctica.

The evidence points to illegal production of the banned chemical, threatening the…

• The ozone hole…