The figure above shows that there are many factors that control CO2 concentrations in the atmosphere. Here we show the average CO2 storage (shown with numbers in square brackets) and exchanges of CO2 between different pools of carbon for the time period between 2000 and 2005. The black arrows indicate natural CO2 exchanges. The red arrows and numbers indicate additional exchanges and storage of carbon resulting from human activity. The exchanges are in petagrams of carbon per year (PgC yr-1). A petagram is a billion metric tons. To put this in perspective, think about a train of railroad hopper cars full of coal. One hopper car will hold about 100 tons of coal which is about 80% carbon. If that hopper car is about 60 feet long (including the couplings), then a train hauling one petagram of carbon as coal would have to be about 156,500 miles long.
The largest source of CO2 to the atmosphere is associated with the burning of fossil fuels and cement manufacturing. A recent effort by the Vulcan project at Purdue University has made a detailed map of CO2 emissions in the United States at a 10km by 10km resolution. The map below shows that population centers are hot spots for CO2 emissions. The Seattle Metropolitan area is the largest source of fossil fuel emissions in the northwestern United States.
|Carbon Cycle Figure provided by C. Sabine (NOAA/PMEL), Emission Figure provided by K. Gurney and Y. Zhou (Purdue University), text provided by C. Sabine (NOAA/PMEL).|