Ambitious or Quixotic?

Economist Nicholas Stern opines on the challenge of climate change. He writes:

The overall targets of 50% reductions in emissions by 2050 (relative to 1990) agreed at the G8 summit in Heiligendamm last June are essential if we are to have a reasonable chance of keeping temperature increases below 2C or 3C.... For a 50% reduction in global emissions by 2050, the world average per capita must drop from seven tonnes to two or three. Within these global targets, even a minimal view of equity demands that the rich countries' reductions should be at least 80% - either made directly or purchased.