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LIFETIME OF EXCESS ATMOSPHERIC CARBON DIOXIDE
Citation:
III, B. AND B. Braswell, Jr. LIFETIME OF EXCESS ATMOSPHERIC CARBON DIOXIDE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-94/459.
Description:
We explore the effects of a changing terrestrial biosphere on the atmospheric residende time of carbon dioxide using three simple ocean carbon cycling models and a model of global terrestrial carbon cycling. e find differences in model behavior associated with the assumption of an active terrestrial biosphere (forest regrowth) and significant differences if we assume a donor-dependent flux from the atmosphere to the terrestrial component (e.g., a hypothetical terrestrial fertilization flux). o avoid numerical difficulties associated with treating the atmospheric carbon dioxide decay (relaxation) curve as being well approximated by a weighted sum of exponential functions, we define the single half-life as the time it takes for a model atmosphere to relax from its present-day value half way to its equilibrium pCO2 value. his scenario-based approach also avoids the use of unit pulse (Dirac Delta) functions which can prove troublesome or unrealistic in the context of a terrestrial fertilization assumption. e also discuss some of the numerical problems associated with a conventional lifetime calculation which is based on an exponential model. e connect our analysis of the residence time of carbon dioxide and the concept of single half-life to the residence time calculations which are based on using weighted sums of exponentials. e note that the single half-life concept focuses upon the early decline of carbon dioxide under a cutoff/decay scenario.