Why is climate change so hard to tackle?

IT IS MORE than a quarter of a century since the leaders of the world, gathered in Rio de Janeiro in 1992, committed their countries to avoiding “dangerous anthropogenic interference in the climate system” by signing the UN convention on climate change. The case for living up to their words has only become stronger. The level of carbon dioxide in the atmosphere grows unremittingly. Average global temperatures have risen, too, to about 1°C above those of the pre-industrial era. The science that links the two is incontestable. Recent extreme-weather events, from floods in Hanoi to fires in California, were made more likely by the change that the climate has already undergone. Things will only get worse—perhaps catastrophically so.