Responses to pollution depend, in part, on concentration. Pour a bag of fertilizer in a little garden pond and you'll kill any fish that may have lived there,

Responses to pollution depend, in part, on concentration. Pour a bag of fertilizer in a little garden pond and you'll kill any fish that may have lived there, and the water will turn to an algae muck quickly. That little pond may never heal. Sprinkle the same bag widely over the surface of a large lake, and the algae, plankton, and seaweed will take up the fertilizer, grow a bit, get eaten by fish, and the whole system will return to equilibrium. Similarly, smog will eventually nucleate rain clouds and fall to earth, noxious ozone will disperse to the upper atmosphere, and volatiles will degrade. True, some effects remain (like the total amount of CO2 in the atmosphere), but there's some benefit to changing "deadly concentrations for millions of people in this small area right this moment" to "long-term effects for a large geographic area in the future". Unfortunately, many kinds of pollution would also be mitigated by being spread out temporally as well as spatially. If we could spread out our CO2 emissions over many millenia, they'd be no problem for the environment to take care of.