Another UN climate change conference ends, another opportunity to save the world goes by. You could be forgiven for barely noticing; expectations were lowered so far that Cancún almost slipped under the radar. But even if it had been talked up like its predecessors, it would struggle for our attention. Climate change is peculiarly, and perhaps fatally, difficult to care about. That is because it's the kind of problem our imaginations are least able to capture and our moral sentiments are least tuned to address. Its effects will be felt most by people not yet born, over periods of time far beyond our imaginative horizons.