In the 1950s the British explorer Richard St. Barbe Baker made an expedition in the Sahara. During St. Barbe's 40,000-kilometre (25,000 mi) expedition he proposed a "Green front" to act as a 50-kilometre-deep (30 mi) tree buffer to contain the expanding desert.[3] The idea re-emerged in 2002, at the special summit in N'Djamena, the capital of Chad on the occasion of World Day to Combat Desertification and Drought.[citation needed] It was approved by the Conference of Leaders and Heads of States members of the Community of Sahel-Saharan States during their seventh ordinary session held in Ouagadougou, the capital of Burkina Faso, on 1–2 June 2005.[4] The African Union endorsed it in 2007 as the ‘Great Green Wall for the Sahara and the Sahel Initiative’ (GGWSSI).[5]