Carbon anthropogenic perturbation

The likelihood of a Little Ice Age carbon-cycle perturbation poses a particular concern for the assumption of pre-anthropogenic steady state in models of the modem carbon cycle. Part of the increase in concentrations of CO2 and CH4 during recent centuries may be due to trends associated with the natural chmate anomaly. This association may seriously affect estimates of eighteenth- and early nineteenth-century human impacts on the... 

Figure 10. The global carbon cycle, showing the reservoirs (in 10 Ions per year) relevant to the anthropogenic perturbation as annual averages over the period 1980 to 1989 (Erswaren et al, 1993 Potter et al, 1993 Siegenthaler and Sarmiento, 1993 Schimel ei al, 2000).

These three fluxes are the direct anthropogenic perturbations to the carbon cycle and are assumed to be negligibly small in preindustrial times. This is an excellent assumption for Ff and Fr, but it also presumes that natural forest fires (F ) were responsible for small emissions of C02. 

In the last 150 years the anthropogenic emission of sulfur has increased dramatically, primarily due to combustion processes [1]. In the 1950s anthropogenic emission surpassed natural emission and the atmospheric sulfur cycle is one of the most perturbed biogeochemical cycles [1,2]. The oceans are the largest natural source of atmospheric sulfur emissions, where sulfur is emitted in a reduced form, predominantly as dimethyl sulfide (DMS) and to a much lesser extent carbonyl sulfide (OCS) and carbon disulfide (CS2) [3]. Ocean emitted DMS and CS2 are initially oxidised to OCS, which diffuses through the troposphere into the stratosphere where further oxidation to sulfur dioxide (SO2), sulfur trioxide (SO3) and finally sulfuric acid (H2SO4) occurs [1-4]. 

Over the past 200 years, the cumulative ocean sequestration of anthropogenic carbon is estimated to be <100 PgC. This sequestration is small (<0.5%) compared to the total carbon inventory in the ocean. To the lowest order, oceanic uptake of anthropogenic CO2 is a small physical-chemical perturbation and does not involve alteration of marine biology, as long as the ocean circulation remains the same. 

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