Carbon dioxide (CO2) distinguishes itself as the fastest growing greenhouse gas in the atmosphere today. Policy decisions and regulation of CO2 emissions depends on our ability to measure the increase in the atmosphere and determine the source of the increase.
Until the late 1950s when high precision measurements began at Mauna Loa, Hawaii, many questioned whether the industrial revolution and the associated increase in fossil fuel burning affected the atmosphere. The Mauna Loa time series of CO2 measurements are the core of a network that has since grown. Recently, the global network of CO2 measurements was expanded (http://www.esrl.noaa.gov/gmd/ccgg/iadv/) into the mid-continent to detect changes in CO2 originating from specific regions within continental boundaries. The new sites include mountain tops, tall towers, and regular aircraft profiles.
The NOAA/ESRL carbon cycle aircraft program made several recent contributions that help clarify carbon cycling processes. At the regional scale the aircraft network used bimonthly measurements of CO2 from 16 aircraft profile sites around North America to create a monthly three-dimensional picture of CO2 over the continent. By combining these observations with a novel budgeting approach to estimate land-to-atmosphere fluxes, researchers found a moderate sink – an area that absorbs CO2 - after subtracting estimated fossil fuel emissions from 2004-2006. Researchers also found that the highest uptake or absorption of CO2 occurs in the Midwest and the Southeast. This agrees with estimates of crop uptake, which proves to be a significant part of the US atmospheric CO2 sink, and of secondary forest regrowth in the East.
The NOAA/ESRL aircraft network has embarked on many recent intensive efforts to explore processes at the 10 to 100 km scale. In particular, air mass-following experiments using small aircraft can be used to observe ground emission or uptake of CO2 in a single air mass as it moves across an agricultural or urban landscape. The net result is a validation of ground-level emissions estimates by direct measurements of changes in atmospheric CO2.