Friday, August 18, 2017

Rise In Atmospheric Carbon Dioxide Should Not Be a Surprise

University of Houston Energy Fellows
Post written by Earl J. Ritchie, Lecturer, Department of Construction Management
Aug. 16, 2017

Many recent articles, such as this New York Times piece, have described the flattening in estimated carbon dioxide emissions from fossil fuels as a possible turning point in anthropogenic greenhouse gas emissions. In the face of this flattening, the unabated rise of atmospheric CO2 has been declared a mystery. A number of possible explanations, such as saturation of carbon sinks and El NiƱo, have been given for the apparent disconnect.

There are two simple explanations: The first is that CO2 emissions from human sources have not actually decreased. The flattening in fossil fuel emissions has been offset by increases due to land use changes, such as logging of forests and increased development. The second is that even if CO2 emissions had flattened, the total amount of CO2 pumped into the atmosphere would not be greatly reduced. The atmospheric CO2 growth rate would slow, but the difference would likely be undetectable in the short term.


Carbon dioxide emissions are estimates rather than facts, however, the bigger issue is that fossil fuel emissions are not the only anthropogenic sources of CO2. The graph below shows that when land use is added, emissions steadily increase.


According to models from the Intergovernmental Panel on Climate Change, short-term carbon sinks – a forest, ocean or other reservoir that can absorb carbon dioxide – could not keep up even if CO2 emissions were significantly reduced. Therefore, atmospheric CO2 continues to increase even if emissions were to be stabilized. This can be seen by the black line in the graph below. The decrease in growth of atmospheric CO2 after emissions are stabilized is gradual and would be difficult to detect over a few years. Actual decrease in concentration requires emissions reductions on the order of 80%.


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