Monthly Atmospheric CO2 Concentration
Atmospheric carbon dioxide concentration fluctuates over months of a year by several ppm from a maximum around May to a minimum around October. This is attributed to Northern hemisphere’s growing season which starts to reduce atmospheric CO2 concentration around May as growth of plants and consumption of atmospheric CO2 by them in Northern hemisphere approach their peak times and then near the end of growing season its effect fades away and the atmospheric CO2 concentrations begins to increase as processes producing CO2 and releasing it into atmosphere never cease. The annual fluctuations of atmospheric CO2 concentration are governed by Northern hemisphere and not Southern hemisphere due to much greater land area and biomass of Northern hemisphere.
In above graph, one can also see increase of atmospheric carbon dioxide concentration over years. In other words, as the years pass, the fluctuations are done around greater average concentrations. Increase of annual atmospheric CO2 concentration as a result of human activities especially deforestation and burning of fossil fuels has contributed to global warming and ocean acidification threatening life on Earth.