How do you recreate the Earth’s biosphere (200 million square miles of surface area with an insanely complex carbon cycle) including a desert, rain forest, savanna, wetland, and ocean (ecosystems that have been evolving separately for billions of years) and make it work inside a 3-acre sealed complex of tinker-toy terrariums? Well, you don’t. But boy, they sure had fun trying.
Biosphere 2 suffered from CO2 levels that fluctuated wildly and most of the vertebrate species and all of the pollinating insects died… also overstocked fish dying and clogging filtration systems, unanticipated condensation making the “desert” too wet, population explosions of greenhouse ants and cockroaches, and morning glories overgrowing the “rainforest”, blocking out other plants… The oxygen inside the facility, which began at 20.9%, fell at a steady pace and after 16 months was down to 14.5%. This is equivalent to the oxygen availability at an elevation of 4,080 meters (13,400 ft)… (Wikipedia)