Identifying Key Sources of Uncertainty in Climate Change Projections

What sources of uncertainty shouldbe included in climate change projections and whatgains can be made if specific sources of uncertaintyare reduced through improved research?DIALOGUE, anintegrated assessment model, has been used to answerthese questions. Central in the approach of DIALOGUEis the concept of parallel modeling, i.e., for eachstep in the chain from emissions to climate change anumber of equivalent models areimplemented. The followingconclusions are drawn:The key source of uncertainty in global temperatureprojections appears to be the uncertainty inradiative forcing models. Within this group ofmodels uncertainty within aerosol forcing models isabout equal to the total forcing of greenhouse gasmodels. In the latter group CO₂ is dominant.The least important source of uncertainty appears tobe the gas cycle models. Within this group of modelsthe role of carbon cycle models is dominant.Uncertainty in global temperature projections hasnot been treated consistently in the literature.First, uncertainty should be calculated as a productof all uncertainty sources. Second, aparticular choice of a base year for global warmingcalculations influences the ranking of uncertainty.Because of this, a comparison of ranking resultsacross different studies is hampered. We argue that`pre-Industrial' is the best choice for studies onuncertainty.There is a linear relationship between maximumuncertainty in the year 2100 and cumulativeemissions of CO₂ over the period 1990–2100:higher emissions lead to more uncertainty.     

Structural softening,mesh dependence,and regularisation in non-associated plastic flow

A severe dependence of numerical simulations on the mesh density is usually attributed to the presence of strain softening in the constitutive relation. However, other material instabilities, like non-associated plastic flow, can also cause mesh sensitivity. Indeed, loss of ellipticity in quasi-static analyses is the fundamental cause of the observed mesh dependence. It has been known since long that non-associated plastic flow can cause loss of ellipticity, but the consequence for mesh sensitivity, and subsequently, for the difficulty of the equilibrium-finding iterative procedure to converge have remained largely unnoticed. We first demonstrate at the hand of a biaxial test structural softening and a marked mesh dependence for an ideally plastic material equipped with a non-associated flow rule. The phenomena are then analysed in depth using an infinitely long shear layer. Finally, it is shown that the mesh effect disappears when the standard continuum model is replaced by a Cosserat continuum, a well-known regularisation method for strain-softening constitutive relations.     

Quantum Instability of Magnetized Stellar Objects

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.     

Climatic changes in areas adjacent to the North Atlantic during the last glacial-interglacial transition (14-9 ka BP): A contribution to IGCP-253

This paper presents a summary of the evidence for climatic changes during the last glacial-interglacial transition (14-9 ka BP) in land areas adjacent to the North Atlantic. It is a synthesis of the results of the 12 regional summaries compiled by contributors to the North Atlantic Seaboard Programme of IGCP-253 that are published separately in this issue of Journal of Quaternary Science. Eighteen palaeotemperature curves are compared and arranged in three transects, one from southern Europe to Spitsbergen, a second from Ireland to Poland, and the third from southern New England to the Labrador-Baffin Shelf area. Ten maps are presented that summarise the synoptic climatic conditions of the region in 500-year time periods. The purpose of the exercise is to examine the extent to which any emerging patterns support the Ruddiman and Mclntyre model of large-scale shifts in the position of the oceanice Polar Front during the last glacial-interglacial transition. Some broad agreement emerges, although the influence of oceanic changes is diminished in areas that lay in close proximity to the Laurentide and Fennoscandian ice sheets. Attention is drawn to limitations in the compilations and to the potential for improved models in the future.     

SHORT COMMUNICATION SOL1:A PROGRAM FOR THE SIMULATION OF COMPLEX EQUILIBRIA USING A PERSONAL COMPUTER

The program SOL1,written in Turbo-PASCAL for use on a personal computers(IBM-PC orcompatible),has been developed for calculating the equilibrium concentrations of the species inmulticomponent ligand-metal mixtures of up to 21 components and 150 species.The main features arethe easy data input system,the possibility of three different tasks(calculating the composition of a singlesolution,simulating titration curves and calculating the species distribution as a function of pH)andprocedures for drawing the calculated curves on Roland DXY plotters.The program has been tested by astudy of six different complex systems.     

Astrophysical limits on gauge invariance breaking in electrodynamics with torsion

General relativistic electrodynamics in a torsion background can give rise to a situation where the photons can ahve a non-zero rest mass and magnetic moment. Astrophysical limits are used to constrain these parameters.