Bryan K. Mignone

A Simple Theory of the Pycnocline and Overturning Revisited

Understanding variability in the meridional overturning circulation requires linking changes in surface forcing and internal mixing to modifications of the thermal structure, differences in the rate of formation of deep waters, and shifts in the locations where these waters are formed. It is thus closely linked to the question of how the ocean circulation is “driven”—which has been debated for many years. In his classic “Physical Geography of the Oceans” (reprinted in 1963), Matthew Fontaine Maury argued that the dominant mechanism for driving such currents was the heating of the tropics and cooling of polar latitudes. In such a picture, one would primarily look to changes in the hydrological cycle or surface heat balance to explain changes in overturning, as in the classic box models of Stommel [1961]. By contrast, Maury fulminated against those who supposed that the ocean circulation was wind-driven, arguing that the variable winds of the Atlantic could never produce the steady Gulf Stream. The idea of a thermally-driven overturning was challenged by Sandstrom [1908] who argued that in a domain where heating occurs at the same level as cooling, a largescale circulation cannot be generated in the absence of A Simple Theory of the Pycnocline and Overturning Revisited

The Gosac Project to Predict the Efficiency of Ocean CO2 Sequestration Using 3-D Ocean Models

Publisher Summary This chapter presents a set of standard injection simulations that were made by eight ocean modeling groups to evaluate the efficiency of the ocean in retaining purposefully sequestered CO 2 . Injection was made simultaneously at seven separate sites; separate 7-site simulations were made for injection at 800 m, 1500 m, and 3000 m. For injection at 3000 m, all models showed 85% or greater global efficiency in year 2200—that is, 100 years after the end of the specified 100-year injection period; at the same time, the 1500-m injection is 60-80% efficient and 800-m injection is only 42-61% efficient. Most of the CO 2 injected at 3000 m was lost from the Southern Ocean (the principal region by which the deep ocean is ventilated); at shallower depths, relatively more was lost sooner, from the northern hemisphere and the tropics. The simulated global injection efficiency at 3000 m is correlated with both the simulated global mean CFC-11 inventory and deep-ocean natural inc. Based on these correlations, the global observational constraints for these two tracers, and model diversity, it appears likely that the range of model-predicted efficiencies would bracket real ocean behavior under the same 3000-m injection scenario.

A ‘safety deposit’ mechanism for US climate policy

US policy makers are currently evaluating options to reduce domestic carbon dioxide emissions, and several economy-wide cap-and-trade proposals have been put forward in the 111th Congress. Despite mounting enthusiasm for cap-and-trade, advocates of this approach have had to defend such proposals against the criticisms that prices in the resulting carbon market will be unstable and that the implied costs of policy might exceed societys willingness to pay for the expected environmental benefits. Allowance borrowing has been proposed as one solution to both of these concerns, with firm-level borrowing intended to mitigate the impacts of transient cost shocks, and system-level borrowing intended to hedge against the risk of early technology bottlenecks. Each of these mechanisms, as proposed, relies upon prescribed constraints, such as interest payments or quantity limits, to protect against overuse. This article introduces a novel mechanism that offers qualitatively similar protection—a firm-level deposit on borrowed allowances that is refundable upon repayment of the emissions debt. However, the deposit mechanism is shown to be both more economically efficient and more effective in mitigating performance risk, when compared to the existing alternatives.