Atmospheric lifetime of carbon dioxide

The yearly carbon dioxide (CO₂) released by animal and plant respiration is in balance with photosynthetic carbon fixation. However, human activities (fuel burning) add about 10% above this equilibrium amount. The excess CO₂ of anthropogenic origin is absorbed in about equal parts by the atmosphere and the surface layer of the oceans. The deep ocean is potentially a large reservoir for CO₂ storage, but the exchange rate between ocean layers is slow (thousands of years). The present concentration of atmospheric CO₂ is 350 ppmv. During the last interglacial period it hovered near 270 ppmv. The range during the Riss and Wurm ice ages was about 180 to 240 ppmv.