Understanding idioms is one of the hardest parts of mastering a language. An idiom is a group of words that together assume a new and different meaning. Native speakers frequently use them in everyday conversations but idioms can confuse students who are not yet fluent.

Secretary of State John Kerry recently called a new report about the growing danger of climate change a “canary in the coal mine.” What does that idiom mean?

Canary in the coal mine

Someone/something that is an early warning of danger.


  • We have a strict new teacher, and many of us want to ask for extra help. We don’t know how she will react, so we sent Jim to ask. He’s like a canary in a coal mine.
  • The melting glacier is a canary in the coal mine for global warming.
State Department/Doug Thompson

Coal miners used to take canaries into coal mines with them. Canaries are more sensitive to dangerous gases than humans are. If the canary died, the miners knew there were dangerous gases present and would leave the mine.

When he used the idiom, Kerry meant that the new report warns of danger if steps are not taken to reduce or halt climate change. His use of the phrase “canary in the coal mine” is especially apt because coal is a fossil fuel, which, when burned, produces greenhouse gases that can contribute to the Earth’s warming. The U.S. takes a leading role in combating climate change. And there’s a lot you can do to help.