“In traditional economic theory, the benefits of reducing emissions take the form of an “externality,” meaning they are external to the local environment because they are spread over the whole world. Our own contributions are often too small to see or feel.

When the problem is an externality, it is, for the most part, futile to ask people to volunteer to fix it — by taking actions like car-pooling or riding a bike to work to cut back on emissions or, in the case of governments, by enacting laws and regulations.

Yes, some individuals with a strong moral compass will take action, and some nations will do so occasionally, but most people and countries will not do so consistently. That’s what the theory says, anyway.

But in a new book, “Climate Shock: The Economic Consequences of a Hotter Planet” (Princeton 2015), Gernot Wagner of the Environmental Defense Fund and Martin L. Weitzman, a Harvard economist, question that assumption. In a proposal that they call the Copenhagen Theory of Change, they say that we should be asking people to volunteer to save our climate by taking many small, individual actions.

Copenhagen has motivated half of its habitants to commute to work by bicycle every day, the Danish government says. How did that come about? A half-century ago, the city’s inhabitants were becoming almost as reliant on cars as people anywhere else. But after the oil crisis of the 1970s, the authors point out, many Copenhagen residents made a personal commitment to ride bicycles rather than drive, out of moral principle, even if that was inconvenient for them.”

How Idealism, Expressed in Concrete Steps, Can Fight Climate Change – NYTimes.com.