The United Nations’ Intergovernmental Panel on Climate Change (IPCC) has warned that the effect of climate change on Africa is likely to be much more severe than on any other continent. Uganda’s president, Yoweri Museveni, has therefore declared climate change an act of aggression by the rich world against the poor one, and demanded compensation (“Drying Up and Flooding Out,” May 12, 2007). “The moral arguments on climate change are even murkier than arguments on other wrongs done to Africa, such as slavery,” you comment, “but Mr. Museveni may have hit on something.” You betcha. After all, IPCC blames industrialization for climate change, and Africa boasts little of it. But the moral argument goes well beyond compensation: it is incumbent upon the rich world to curb the greenhouse gasses so as to lessen the adverse effects of climate change in the poor world, where millions of people are in peril. This is a moral argument par excellence, and there is nothing murky about it.