<P> The most direct method for measuring atmospheric carbon dioxide concentrations for periods before instrumental sampling is to measure bubbles of air ( fluid or gas inclusions ) trapped in the Antarctic or Greenland ice sheets . The most widely accepted of such studies come from a variety of Antarctic cores and indicate that atmospheric CO concentrations were about 260 -- 280 ppmv immediately before industrial emissions began and did not vary much from this level during the preceding 10,000 years . The longest ice core record comes from East Antarctica , where ice has been sampled to an age of 800,000 years . During this time , the atmospheric carbon dioxide concentration has varied between 180 -- 210 ppm during ice ages , increasing to 280 -- 300 ppm during warmer interglacials . The beginning of human agriculture during the current Holocene epoch may have been strongly connected to the atmospheric CO increase after the last ice age ended , a fertilization effect raising plant biomass growth and reducing stomatal conductance requirements for CO intake , consequently reducing transpiration water losses and increasing water usage efficiency . </P>
<P> The most direct method for measuring atmospheric carbon dioxide concentrations for periods before instrumental sampling is to measure bubbles of air ( fluid or gas inclusions ) trapped in the Antarctic or Greenland ice sheets . The most widely accepted of such studies come from a variety of Antarctic cores and indicate that atmospheric CO concentrations were about 260 -- 280 ppmv immediately before industrial emissions began and did not vary much from this level during the preceding 10,000 years . The longest ice core record comes from East Antarctica , where ice has been sampled to an age of 800,000 years . During this time , the atmospheric carbon dioxide concentration has varied between 180 -- 210 ppm during ice ages , increasing to 280 -- 300 ppm during warmer interglacials . The beginning of human agriculture during the current Holocene epoch may have been strongly connected to the atmospheric CO increase after the last ice age ended , a fertilization effect raising plant biomass growth and reducing stomatal conductance requirements for CO intake , consequently reducing transpiration water losses and increasing water usage efficiency . </P>
the pre-industrial level of co2 in the atmosphere in ppmv is about
the pre-industrial level of co2 in the atmosphere in ppmv is about
260 -- 280 ppmv
260 -- 280 ppmv