Ways to stop the earth from overheating are far from easy

Indigenous Mayan villages in Chiapas, in southern Mexico, have discovered a new cash crop. It certainly won't bring them the riches that gold brought earlier Amerindian civilisations, but it should give them a new source of income. Next to their fields of beans and maize they are planting trees: not, as you might expect, for timber - although they will yield that too - but for the environmental services they provide.