Carbon Cycle still has many uncertainties

How much of the increase in carbon dioxide concentration in the atmosphere is due to the use of fossil fuels is not as certain as many would like to believe. The role of the oceans both in the emission and the absorption of carbon dioxide is far from being understood or quantified. Emissions due to fossil fuel combustion are of the same magnitude as just the error band surrounding the emissions from the oceans and  from the emissions due to transpiration. The primary sources of carbon dioxide in the atmosphere are the oceans and transpiration. The assumption that these emissions are in balance with the absorption by the oceans and plant life is just an assumption based on an assumed equilibrium which is far from certain. I posted a few weeks ago

…. The general assumption is that about 40% of man-made carbon dioxide shows up as this increase with the remainder being absorbed by the enhanced action of sinks.

SOURCES AND SINKS OF CARBON DIOXIDE

The justification for this conclusion is supported by measurements of the falling proportion of  13C  in the atmosphere which is taken to signal the appearance of CO2 from fossil fuel emissions. …… 

The correlation of changes in δ13C with ENSO events and the comparison with a simple model of a series of cascades suggest that the changes in δ13C in the atmosphere have little to do with the input of CO2 emissions from the continuous use of fossil fuels.

Even though the combustion of fossil fuels only contributes less than 4% of total carbon dioxide production (about 26Gt/year of 800+GT/year), it is usually assumed that the sinks available balance the natural sources and that the carbon dioxide concentration – without the effects of man – would be largely in equilibrium.  (Why carbon dioxide concentration should not vary naturally escapes me!). It seems rather illogical to me to claim that sinks can somehow distinguish the source of carbon dioxide in the atmosphere and preferentially choose to absorb natural emissions and reject anthropogenic emissions! Also, there is no sink where the absorption rate would not increase with concentration.

Carbon dioxide emission sources (GT CO2/year)

  • Transpiration 440
  • Release from oceans 330
  • Fossil fuel combustion 26
  • Changing land use 6
  • Volcanoes and weathering 1

Carbon dioxide is accumulating in the atmosphere by about 15 GT CO2/ year. The accuracy of the amounts of carbon dioxide emitted by transpiration and by the oceans is no better than about 2 – 3% and that error band (+/- 20GT/year)  is itself almost as large as the total amount of emissions from fossil fuels. ….. 

Two new papers – in completely different fields – highlight the uncertainty in carbon dioxide emissions from the oceans and from plant and animal life:

1. Interannual variability in sea surface temperature and fCO2 changes in the Cariaco Basin Y.M. Astor et al, Deep-Sea Res. II (2013), http://dx.doi.org/10.1016/j.dsr2.2013.01.002i

The Hockey SchtickA new paper published in Deep-Sea Research finds the ocean is a net source of CO2 to the atmosphere, the opposite of claims by climate alarmists that the ocean removes CO2 from the atmosphere. According to the authors, “At the [research] site, the ocean is primarily a source of CO2 to the atmosphere, except during strong upwelling events.” The paper also notes, “Astor et al.(2005) observed the interactions between physical and biochemical parameters that lead to temporal [over time] variations in fCO2 [CO2 flux from the] sea, finding that even during periods of high production, the CO2 flux between the ocean and the atmosphere decreased but remained positive, i.e. CO2 escaped from the ocean to the atmosphere.” 

The paper corroborates prior work by SalbyHumlum et alFrölicher et alCho et alCalder et alFrancey et alAhlbeckPetterssonand others demonstrating that man-made CO2 is not the driver of atmospheric CO2. This new work confirms the primary source of atmospheric CO2 is out-gassing from the oceans, which is due to decreased solubility with increased temperature.

2. Michael S. Strickland, Dror Hawlena, Aspen Reese, Mark A. Bradford, and Oswald J. Schmitz. Trophic cascade alters ecosystem carbon exchangePNAS, 2013 DOI:10.1073/pnas.1305191110

EurekAlert: …. The study, conducted by researchers at the Yale School of Forestry & Environmental Studies, comes out this week in the Proceedings of the National Academy of Sciences. It looks at the relationship between grasshoppers and spiders—herbivores and predators in the study’s food chain—and how it affects the movement of carbon through a grassland ecosystem. Carbon, the basic building block of all organic tissue, moves through the food chain at varying speeds depending on whether it’s being consumed or being stored in the bodies of plants. However, this pathway is seldom looked at in terms of specific animal responses like fear from predation. …… 

….. The study found that the presence of spiders drove up the rate of carbon uptake by the plants by about 1.4 times more than when just grasshoppers were present and by 1.2 more times than when no animals were present. It was also revealed that the pattern of carbon storage in the plants changed when both herbivores and carnivores were present. The grasshoppers apparently were afraid of being eaten by the spiders and consumed less plant matter when the predators were around. The grasshoppers also shifted towards eating more herbs instead of grass under fearful scenarios.

At the same time, the grasses stored more carbon in their roots in a response to being disturbed at low levels when both herbivores and carnivores were present. In cases where only herbivores were present, the plants stored less carbon overall, likely due to the more intense eating habits of the herbivores that put pressure on plants to reduce their storage and breathe out carbon more. These stress impacts, then, caused both the plants and the herbivores to change their behaviors and change the composition of their local environment.

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