Economist: IN 1990 John Latham, a cloud physicist, published a short article in Nature under the headline Control of Global Warming? It argued that if low-lying maritime clouds were made a bit brighter, the Earth could be cooled enough to make up for the increased warming caused by emissions of greenhouse gases. The brightening was to be achieved by wafting tiny sea-salt particles up into the clouds from below; by acting as cloud condensation nuclei (CCN) they would increase the number of water droplets...