Carbon Cycle: Emissions from forest clearance underestimated, land absorption underestimated

Two new papers just published show that the carbon cycle is far from being certain. We still have large uncertainties regarding the sources of carbon dioxide emissions and their magnitude and the sinks where, and mechanisms by which, carbon dioxide is absorbed. One in Global Change Biology. shows that emissions due to forest clearance have been underestimated by some 40% while the second in Nature suggests that there are large land sinks for carbon dioxide in the Southern Hemisphere (paywalled but reported here) which have largely been ignored by climate models.

  1. The amount of carbon lost from tropical forests is being significantly underestimated, a new study reports. In addition to loss of trees, the degradation of tropical forests by selective logging and fires causes large amounts of “hidden” emissions. 
  2. they find that land sinks for CO2 are keeping up with the increase in CO2 emissions, thus modeled projections of exponential increases of CO2 in the future are likely exaggerated. 

The “settled science of climate” is a an edifice tottering on two unproven hypotheses:

  1. That carbon dioxide concentration in the atmosphere is a key driver of global temperature, and
  2. That man-made emissions of carbon dioxide (primarily fossil fuel combustion) are the key contributor to concentration in the atmosphere.

If either of these two assumptions are incorrect, the entire edifice of climate science and climate policy comes tumbling down.

The first now looks decidedly weak. For almost 20 years now global temperatures have stagnated (and show a slight negative trend) while carbon dioxide emissions from combustion have increased sharply. Carbon dioxide concentration has also continued to increase but at a much lower rate than the rate of man-made emissions. No doubt carbon concentration has some impact but it is clearly far from being a key driver of global temperature.

The second assumes that “natural emissions” and absorption are roughly in balance and therefore it must be fossil fuel combustion which is responsible for the increase of carbon dioxide concentration. But the Carbon balance of the earth is far from certain. Volcanic de-gassng of CO2 has been grossly underestimated. The mass of CO2 absorbing bio-mass in the oceans has also been underestimated and remains still highly uncertain.

The error bands surrounding “natural” emissions are of the same magnitude as man-made emissions. Absorption of Carbon dioxide by the oceans and the biological life (algae) in the oceans are, at best, relatively uncertain estimations.

ktwop: 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. 

…… 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. ….. 

The demonisation of fossil fuel combustion is based on belief and not on evidence. The carbon dioxide assumptions which are the foundations of the climate orthodoxy are unsound.

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