​as of 2015 what is the approximate co2 level in earth’s atmosphere
Carbon dioxide in Earth's atmosphere Over the past 400,000 years, CO2 concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Following the start of the Industrial Revolution, atmospheric CO2 concentration has increased to over 400 parts per million and continues to increase, causing the phenomenon of global warming.[10] The daily average concentration of atmospheric CO2 at Mauna Loa Observatory first exceeded 400 ppm on 10 May 2013[11][12] although this concentration had already been reached in the Arctic in June 2012.[13] It currently constitutes about 0.041% by volume of the atmosphere, (equal to 410 ppm) [14][15][16][17][18] which corresponds to approximately 3200 gigatons of CO2, containing approximately 870 gigatons of carbon. Each part per million by volume of CO2 in the atmosphere thus represents approximately 2.13 gigatonnes of carbon.[19] The global mean CO2 concentration is currently rising at a rate of approximately 2 ppm/year and accelerating.[14][20][21] There is an annual fluctuation of about 3â€“9 ppm which is negatively correlated with the Northern Hemisphere's growing season. The Northern Hemisphere dominates the annual cycle of CO2 concentration because it has much greater land area and plant biomass than the Southern Hemisphere. Concentrations reach a peak in May as the Northern Hemisphere spring greenup begins, and decline to a minimum in October, near the end of the growing season.[21][22]