11/11/2012
Global Carbon Budget
There is a lot of talk in the scientific community about carbon sinks and sources. In fact, I have posted about the role of soils in the carbon budget on the The Earth Story before, however this post will broaden the perspective and take a look at the global balance of carbon sources and sinks. A carbon source is anything that is releasing more CO2 than it captures and stores, this includes deforestation and fossil fuel combustion. A carbon sink is anything that absorbs more C02 than it releases, such as soils and oceans.
Global carbon cycles are complex and not fully understood; I will report on significant and our most understood aspects of the global carbon budget. The primary units of this post are Gt C y-1 which is gigatons of carbon per year. The largest reservoirs of carbon is the atmosphere at 750 Gt C, (+3.2 Gt C y-1), then soil and detritus at 1580 Gt C, and the largest; oceans 39,000 Gt C (+2 Gt C y-1).
The atmosphere loses about 100 Gt C y-1 to photosynthesis. Forests (a 610 Gt C reservoir) convert much of this to woody organic matter, and respire about 50-60 Gt C y-1 back to the atmosphere. Deforestation accounts for about 1.6 Gt C y-1 being released to the atmosphere, and fossil fuel combustion, 5.4 Gt C y-1. Deforestation and fossil fuel combustion are not natural within the carbon cycle, and are unchecked carbon sources.
Oceans are quite special in the carbon budget, as they are natural carbon sinks; although many believe that will not last much longer. Through physiochemical diffusion, oceans release 90 Gt C y-1 to the atmosphere, but absorb 92 Gt C y-1.
The global budget can be simplified by looking at source and sink fluxes. The C02 source flux is 5.4 Gt C y-1 from fossil fuel combustion and 1.6 from deforestation, totaling 7.0 Gt C y-1. The C02 sink flux in the atmospheric is 3.2 Gt C y-1 and 2.0 Gt C y-1 from oceans, totaling 5.2. These numbers would lead us to a global imbalance of 1.8 Gt C y-1 increase to the atmosphere.
This may be a simplification of the process, using slightly out-of-date numbers (from a lecture). But they give us insight into the major factors in the global carbon budget, and point us to areas in need of scientific attention.
-Greg Aegis
Further Reading
Carbon Dioxide Information Analysis Center - http://cdiac.ornl.gov/
http://fluxnet.ornl.gov/
Photo Credit
http://earthobservatory.nasa.gov
