The movers and shakers of the world economy are trying to close in on the magic number of $100 billion a year to fight climate change as they meet this week in Peru. But with the world well shy of that target, everyone seems to think the rest of the money should come from somewhere else. The global talks on fighting climate change have stumbled over the issue of getting money to the countries that are most vulnerable to global warming and often least responsible for causing it. Wealthy nations have pledged to come up with $100 billion a year by 2020, but with two months to go to clutch United Nations climate talks, a new report this week found the world is less than two-thirds of the way there.