claim: "...there is the contention by Wolfgang Knorr of the Department of Earth Sciences at the University of Bristol in England that carbon dioxide levels in the atmosphere are about where they were 160 years ago." (as quoted by Ken Ward Jr.)
evidence: In this symbiotic relationship, the zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host while the cnidarian gains photosynthetic capability and increased production of calcium carbonate, a substance of great importance to stony corals.