Potential Dependence of Global Warming on the Residence Time (RT) in the Atmosphere of Anthropogenically Sourced Carbon Dioxide

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The driver for this study is the wide-ranging published values of the CO₂ atmospheric residence time (RT), τ, with the values differing by more than an order of magnitude, where the significance of the difference relates to decisions on whether (1) to attempt control of combustion-sourced (anthropogenic) CO₂ emissions, if τ > 100 years, or (2) not to attempt control, if τ ∼ 10 years. This given difference is particularly evident in the IPCC First 1990 Climate Change Report where, in the opening policymakers summary of the report, the RT is stated to be in the range of 50−200 years, and (largely) on the basis of that, it was also concluded in the report and from subsequent related studies that the current rising level of CO₂ was due to combustion of fossil fuels, thus carrying the, now widely accepted, rider that CO₂ emissions from combustion should therefore be curbed. However, the actual data in the text of the IPCC report separately states a value of 4 years. The differential of these two times is then clearly identified in the relevant supporting documents of the report as being, separately (1) a long-term (∼100 years) adjustment or response time to accommodate imbalance increases in CO₂ emissions from all sources and (2) the actual RT in the atmosphere of ∼4 years. As a check on that differentiation and its alternative outcome, the definition and determination of RT thus defined the need for and focus of this study. In this study, using the combustion/chemical-engineering perfectly stirred reactor (PSR) mixing structure or 0D box for the model basis, as an alternative to the more commonly used global circulation models (GCMs), to define and determine the RT in the atmosphere and then using data from the IPCC and other sources for model validation and numerical determination, the data (1) support the validity of the PSR model application in this context and, (2) from the analysis, provide (quasi-equilibrium) RTs for CO₂ of ∼5 years carrying C12 and ∼16 years carrying C14, with both values essentially in agreement with the IPCC short-term (4 year) value and, separately, in agreement with most other data sources, notably, a 1998 listing by Segalstad of 36 other published values, also in the range of 5−15 years. Additionally, the analytical results also then support the IPCC analysis and data on the longer “adjustment time” (∼100 years) governing the long-term rising “quasi-equilibrium” concentration of CO₂ in the atmosphere. For principal verification of the adopted PSR model, the data source used was the outcome of the injection of excess ¹⁴CO₂ into the atmosphere during the A-bomb tests in the 1950s/1960s, which generated an initial increase of approximately 1000% above the normal value and which then declined substantially exponentially with time, with τ = 16 years, in accordance with the (unsteady-state) prediction from and jointly providing validation for the PSR analysis. With the short (5−15 year) RT results shown to be in quasi-equilibrium, this then supports the (independently based) conclusion that the long-term (∼100 year) rising atmospheric CO₂ concentration is not from anthropogenic sources but, in accordance with conclusions from other studies, is most likely the outcome of the rising atmospheric temperature, which is due to other natural factors. This further supports the conclusion that global warming is not anthropogenically driven as an outcome of combustion. The economic and political significance of that conclusion will be self-evident.