Fascinating satellite images from NASA show fires raging across West Africa as farmers carry out the cyclical clearing of last year's crop remains. Each hot spot, which appears as a red mark, is an area where the thermal detectors on the Suomi NPP satellite recognised temperatures higher than background. When accompanied by plumes of smoke, as in the images, such hot spots are diagnostic for fire. The location, widespread nature, and number of fires suggest that these fires were deliberately set to manage land. The progression of agricultural activity can been seen by comparing images captured on 14 March with those taken on 30 April. Farmers often use fire to return nutrients to the soil and to clear the ground of unwanted plants. The fires produce smoke that degrades air quality.