NEW YORK — Imagine that a huge asteroid is hurtling toward Earth. Scientists tell us that there is a 10 percent chance of a collision in 10 years and the consequences of its impact will be catastrophic. Your government advises you not to panic and reminds you that there is a 90 percent chance that the asteroid will miss Earth. Do you decide not to worry, or do you demand that your government mobilize all resources at its disposal to eliminate the risk?

We know that even in this fictitious — although not unthinkable — scenario, a variant of which constitutes the opening of Scott Barrett's excellent book on global issues, the world would act to find a solution without a second thought. Governments would invest in whatever it takes to divert the asteroid from its predicted trajectory.

The analogy with climate change is not perfect. Potential catastrophe for the world as a whole is a more long-term risk. On the other hand, it would be more accurate to compare climate change to a family of asteroids, a big one threatening us all, but further away, and a group of medium-size ones that are likely to hit the poorest countries at lower latitudes much sooner and with much greater certainty than the large one.