Times (UK): A few weeks ago, in central Mozambique, I stood in a clearing of blackened tree stumps in a landscape of weeds. This was a classic example of "slash-and-burn’ agriculture, in which dirt-poor farmers constantly move on from depleted fields to hack new ones out of virgin forest. A few miles away, thanks to a carbon-trading scheme, another community of farmers was working differently. Through a few simple agricultural techniques they were able to go on cropping the same land year after …