At an environmental summit being held this week in Rio de Janeiro, Latin American and Caribbean countries are forging an alliance to pressure developed nations to foot most of the bill for the planet’s ailing ecosystems. During the 1992 Rio Earth Summit, industrialized nations pledged to spend 0.7 percent of their gross domestic products on sustainable development in the developing world, but that promise has gone unmet except by a handful of European nations. Representatives at this week’s summit say that in the last decade, Latin America has matured politically and is ready to demand fulfillment of the pledge. The coalition plans to make its case during the 10th anniversary of the Earth Summit, to be held next year in South Africa.