Convexity Properties of the Moment Mapping Re-examined

Consider a Hamiltonian action of a compact Lie group on a compact symplectic manifold. A theorem of Kirwan's says that the image of the momentum mapping intersects the positive Weyl chamber in a convex polytope. I present a new proof of Kirwan's theorem, which gives explicit information on how the vertices of the polytope come about and on how the shape of the polytope near any point can be read off from infinitesimal data on the manifold. It also applies to some interesting classes of noncompact or singular Hamiltonian spaces, such as cotangent bundles and complex affine varieties.Comment: 36 pages, 3 figures, LaTeX-2e. Revised version. A number of errors corrected and references added. To appear in Adv. in Mat

A Climate-Change Policy Induced Shift from Innovations in Energy Production to Energy Savings

We develop an endogenous growth model with capital, labor and energy as production factors and three productivity variables that measure accumulated innovations for energy production, energy savings, and neutral growth. All markets are complete and perfect, except for research, for which we assume that the marginal social value exceeds marginal costs by factor four. The model constants are calibrated so that the model reproduces the relevant trends over the 1970-2000 period. The model contains a simple climate module, and is used to assess the impact of Induced Technological Change (ITC) for a policy that aims at a maximum level of atmospheric CO2 concentration (450 ppmv). ITC is shown to reduce the required carbon tax by about a factor 2, and to reduce costs of such a policy by about factor 10. Numerical simulations show that knowledge accumulation shifts from energy production to energy saving technology.Induced technological change, Environmental taxes, Partial equilibrium

The Value of ITC under Climate Stabilization

We assess the effect of ITC in a global growth model, DEMETER-1CCS, with learning by doing where energy savings, an energy transition, and carbon capturing and sequestration (CCS) are the main options for emissions reductions. The model accounts for technology based on learning by doing embodied in capital installed in previous periods. We have run five scenarios, one baseline scenario in which climate change policy is assumed absent, and four stabilization scenarios in which atmospheric CO2 concentrations are stabilized at 550, 500, 450, and 400 ppmv. We find that the timing of emission reductions and the investment strategy is relatively independent of the endogeneity of technological change. The vintages structure of production is more important. But ITC reduces costs by about factor 2, though these benefits only materialize after some decades.Energy, Carbon taxes, Endogenous technological change, Niche markets

Induced Technological Change under Technology Competition

We develop a partial one-sector model with capital, natural resources, and labor as production factors, and endogenous technological change through research. Production exhibits increasing returns to scale. We compare the response of output and resource use to a change in resource prices with and without induced technological change (ITC). It is shown that induced technological change is insignificant in reducing resource use when there is one representative technology and output demand is inelastic to prices. In contrast, substantial gains from ITC appear when we allow for two competing technologies that can be employed for production, while these technologies are good substitutes. Also, in case of two technologies, conditions are specified under which multiple balanced growth paths exist, and it is shown that because of ITC, a temporary resource tax can lock out the economy from a resource intensive path and lock in to a resource extensive path.Induced technological change, environmental taxes, partial equilibrium