ESA satellites have been continuously surveying fires burning across the Earth's surface for the last 10 years. More than 50 million hectares of forest are burnt annually.
Some fun facts to give some perspective. Forests cover roughly 30% of land in the world. There are about 5 billion hectares of forest in the world. Roughly half of the world's forests are in the tropics. 50 million hectares of burning represents 1% of the total worldwide forest total.
Story Link-http://www.esa.int/esaEO/SEMRBH9ATME_environment_0 .html