Global Carbon Cycle Carbon dioxide (CO2) is input to the atmosphere by respiration of living organisms, by outgassing of magmatic volatiles from volcanoes, hot springs, etc. and by decomposition of sediments (diagram). Carbon dioxide is fixed from the atmosphere by photosynthesis, by dissolution in water and by weathering of silicate rocks. Too little carbon dioxide, or The balance between these competing processes is extremely sensitive to changes in global temperature, which is directly related to the amount of CO2 in the atmosphere. Without plate tectonics returning CO2 into the atmosphere at volcanoes, eventually all the CO2 would disappear from the atmosphere, and be fixed into the lithosphere. This would lead to a dramatic drop in global temperature, resulting in the expansion of the Arctic and Antarctic icecaps to cover much of the ocean and land surfaces. Following on from this, a negative feedback loop would be initiated: increased amounts of sunlight would be reflected back from the Earth's surface (since ice is much more reflective than water or rock), leading to a further cooling, formation of more ice, more sunlight reflection, etc., in an increasing downward spiral to disaster. Too much carbon dioxide? In the opposite sense, too much CO2 (and certain other gases) in the atmosphere will lead to an equally undesirable "greenhouse" effect. While the Sun's visible light is able to penetrate the atmosphere, the infrared radiation (heat) from the Earth's surface cannot escape into space since the atmosphere is much less transparent (more "opaque") to this radiation. The outcome is a gradual heating of the atmosphere with all the associated effects of climatic changes, melting of the icecaps and corresponding higher water levels and resulting flooding of lower lying areas.