Project Syndicate: In 2009, the worlds rich countries pledged to mobilize $100 billion a year by 2020 to help poor countries tackle climate change. Since then, that promise has come to be regarded as a key test of the developed worlds resolve to do its part in the fight against global warming. Reaching the $100 billion target is important. Poor countries must believe that rich countries will honor their pledges. Otherwise, the prospects for an effective international agreement at the United Nations Climate Change...