Biosphere 2 Laboratory (B2L), Arizona, USA. The B2L is a closed system, the largest available, for research into the dynamics of ecological systems. It comprises several greenhouse buildings for four main biomes (ecological communities). Three of the biomes are seen (from right): rainforest, ocean and desert. The South Lung (far left) is one of two lung structures that vary in volume to maintain atmospheric air pressure in the closed system. B2L, covering over 76,000 square metres, was built in the late 1980s and included people in two closed system experiments. It is now operated by Columbia University as an open flow system to study climate change in Biosphere 1, the Earth.