Regulating global temperature may be mission impossible

ON climate change, curb your enthusiasm. It's not that the recent international conference in Paris didn't take significant steps to check global warming. It did. Nearly 200 countries committed to reduce their greenhouse gas emissions. The goal of limiting warming to two degrees Celsius from pre-industrial times was reaffirmed. The trouble is that what's being attempted is so fundamentally difficult that even these measures may be wildly unequal to the task.

What's being attempted, of course, is the wholesale replacement of the world economy's reliance on fossil fuels for four-fifths of its energy. To be sure, the shift is envisioned to take decades, four or five at a minimum. Still, the vast undertaking may exceed human capability.

Hence, a conundrum. Without energy, the world economy shuts down, threatening economic and social chaos. But the consequences of climate change, assuming the scientific consensus is accurate, are also grim - from rising sea levels (threatening coastal cities) to harsher droughts (reducing food supplies).