I am constantly dropping the term “climate change” into conversations with strangers. I may talk about my own work or relate it to the weird weather or some other issue that is hogging a prime spot in their pool of worry. I am very relaxed and casual about it — after all, no one wants to find herself sitting next to a zealot on a long-distance train journey.

Really, though, it doesn’t seem to matter how I say it, because the result is almost always the same: The words collapse, sink, and die in midair, and the conversation suddenly changes course. It is like an invisible force field that you discover only when you barge right into it. Few people go that far, because, without ever having been told, they have somehow learned that this topic is out-of-bounds. That is why they know that if someone else inadvertently enters this zone, it is a good idea to find something new to talk about.

In America I find that the native friendliness dissipates the instant the words “climate change” enter a conversation. If I am talking to a couple, one person will continue to talk with me (it would be rude not to) while the other will instantly turn away and find some adjacent distraction.

When pressed, two thirds of people admit that they rarely or never talk about it, even inside the close circle of their friends and family members. Another survey found that a quarter of people have never discussed climate change with anyone at all.

My friend Mayer Hillman, a senior fellow at the Policy Studies Institute and a passionate climate change campaigner, was attending a dinner party with retired professionals like himself. People were talking about their latest holiday trips, and Mayer could not resist bringing up the issue of climate change and the impacts of their airline flights on future generations.

The room went very quiet. Then a guest decided to break the ice. “My word,” she said, “what a lovely spinach tart.” Oh yes, everyone agreed emphatically, it was a very lovely spinach tart. They spent the next ten minutes talking about the tart, the fresh spinach, and the recipe.