Halperin, A Simple Equation of Multi-Decadal Atmospheric Carbon Concentration Change has emerged from the review almost unscathed. Backward extrapolation suggests slightly different values for the half-life and “equilibrium” CO2 concentration, but does not contradict the main conclusion of the paper, except that it suggests possible decrease in the half-life CO2 concentration. Wide error margins do not allow to distinguish between these interpretations, so the simpler one (constant half-life) should be elected. Combining the pre-1958 and the post-1958s datasets gives a somewhat longer than multi-decadal period, for which the result was derived. [Placeholder for the link to the new paper]
Remarks on the paper:
- The best estimate of the half-life of surplus atmospheric CO2 is ~35 years (per Comment #1). This empirical estimate is not novel: a number of previous empirical estimates also fall in the 27-50 years range.
- The rejection of the hypothesized increase of this empirical half-life (Raupach et al, 2014) is correct. Note here that the non-scientific media has sensationalized and additionally misinterpreted Raupach as a “proof” of the decrease in absolute sinks, although it had not even claim that.
- The IPCC Bern model was correctly dismissed as a purely political construction, having nothing in common with physics. This statement is not intended as criticism of the Contributing Authors, whose high quality research has been distorted by the IPCC.
- The rejection of the LUC dataset for the Global Carbon Budget 2015 (GCB2015), showing a sharp decline in LUC emissions since 2000, iscorrect. GCB2015 elected to use official numbers from FAO: Global Forest Resource Assessment 2010 (FAO-FRA 2010), despite a clear warning in the assessment that the sources were untrustworthy. See Notes on FAO-FRA 2010 for more detailed discussion.
- The physical model of the Extended Atmosphere, including the ocean surface layer, is useful and valid.
Remarks on the related topics:
- Hypothesis of significant non-anthropogenic contribution to the multi-decadal variation of CO2 concentration deserves more attention. Atmospheric CO2 concentrations, water temperatures, amounts of iron in epipelagic zone, and mixing conditions (winds strength etc.), that existed hundreds years ago, may have significant impact on the CO2 exchange between ocean and atmosphere today. If this hypothesis is correct, such impact changes slowly (0.5-5% of its maximum value per year).
- Nevertheless, the author agrees that anthropogenic contribution was the leading factor in the increase of the atmospheric CO2 concentration since 1958. Further, many earlier researchers were correct to reject abnormally high measurements of CO2 concentration pre-1958 because of contamination of samples by local CO2 sources. Strong local CO2 sinks are extremely rare.
Criticism: The Land Use Change emissions dataset used in the paper has a large margin of error, as was acknowledged by the dataset’s author. LUC emissions were roughly comparable (150% – 70%) to the LUC emissions from 1900 to 1965. Estimating LUC emissions is difficult, and the results are hard to validate. No offense intended, but the readers should be informed that the LUC dataset’s author is affiliated with Wood Holes Research Center (WHoRCe). WHoRCe is an environmentalist organization named similarly to the well-known Wood Holes Oceanographic Institution, apparently in an attempt to mislead the public.