Measuring climate change turns out to be a thorny problem, and so it is hardly surprising that measuring its impact on humans is an even pricklier one. “Seat-of-the-pants estimates will not be enough to cool the world,” you haughtily introduce the first such attempt by Kofi Annan’s Global Humanitarian Foundation (“Go On, Guess,” June 2, 2009). True, but the task is still worthwhile. The report’s key estimate that two-fifths of an expected increase in weather-related disasters will be related to climate change is thus a useful attempt to pin the problem down rather than useless guesswork. Further research will surely give us better figures, but we must start somewhere. And the eminent authors behind the “Human Impact Report” do precisely that. Besides, lampooning “hazardous estimates” will not be enough to cool the world, either.