ABSTRACT

Human activities, particularly the utilization of fossil fuels for energy are quickly changing the trace gas composition of Earth’s atmosphere. The current concentration of carbon dioxide (CO2) in the atmosphere has increased 40% since the 280 parts per million (ppm) estimated around 1750, at the beginning of the Industrial Era (Le Quéré et al. 2012). In May 2013, the concentration measured at Mauna Loa Observatory, Hawaii, reached 400 ppm (see www.CO2Now.org), which means that for the fi rst time in the history of humankind, on average for every one million molecules in the atmosphere, 400 of them were CO2 molecules. In fact, for the past ten years the average annual rate of increase has been 2.07 parts per million (ppm), which is more than double the increase in the 1960s (0.9 ppm year-1). Considering the overall mass of the atmosphere 5.148 x 1021 grams (Trenberth and Smith 2005), and correcting by the molecular mass, every single ppm of CO2 in our atmosphere corresponds approximately to 7.8 petagrams (Pg) of CO2 (7.822 x 10

15 grams of CO2) or 2.134 petagrams of C (carbon).1 This means that on average and at the current increase rates,

15.6 petagrams of CO2 or 4.2 petagrams of carbon are added yearly to our atmosphere and are not being absorbed by other CO2 reservoirs.