The Consequences of CO2 Stabilisation for the Impacts of Climate Change

This paper reports the main results of an assessment of the global-scale implications of the stabilisation of atmospheric CO₂ concentrations at 750 ppm (by 2250) and 550 ppm (by 2150), in relationto a scenario of unmitigated emissions. The climate change scenarios were derived from simulation experiments conducted with the HadCM2 global climate model and forced with the IPCC IS92a, S750 and S550 emissions scenarios. The simulated changes in climate were applied to an observed global baseline climatology, and applied with impacts models to estimate impacts on natural vegetation, water resources, coastal flood risk and wetland loss, crop yield and food security, and malaria. The studies used a single set of population and socio-economic scenarios about the future that are similar to those adopted in the IS92a emissions scenario.An emissions pathway which stabilises CO₂ concentrations at 750 ppmby the 2230s delays the 2050 temperature increase under unmitigated emissions by around 50 years. The loss of tropical forest and grassland which occurs by the 2050s under unmitigated emissions is delayed to the 22nd century, and the switch from carbon sink to carbon source is delayed from the 2050s to the 2170s. Coastal wetland loss is slowed. Stabilisation at 750 ppm generally has relatively little effect on the impacts of climate change on water resource stress, and populations at risk of hunger or falciparum malaria until the 2080s.A pathway which stabilises CO₂ concentrations at 550 ppm by the 2170s delays the 2050 temperature increase under unmitigated emissions by around 100 years. There is no substantial loss of tropical forest or grassland, even by the 2230s, although the terrestrial carbon store ceases to act as a net carbon sink by around 2170 (this time because the vegetation has reached a new equilibrium with the atmosphere). Coastal wetland loss is slowed considerably, and the increase in coastal flood risk is considerably lower than under unmitigated emissions. CO₂ stabilisation at 550 ppm reduces substantially water resource stress, relative to unmitigated emissions, but has relatively little impact on populations at risk of falciparum malaria, and may even cause more people to be at risk of hunger. While this study shows that mitigation avoids many impacts, particularly in the longer-term (beyond the 2080s), stabilisation at 550 ppm appears to be necessary to avoid or significantly reduce most of the projected impacts in the unmitigated case.     

Peralkaline acid liquids: A petrological study

Electron-microprobe analyses of the feldspars and associated ferromagnesian minerals in the peralkaline volcanics, comendites and pantellerites, are presented together with new data on the major and trace-elements of the rocks and residual glasses. The feldspar phenocrysts in the pantellerites span a narrower range (Or₃₃–Or₃₉) than those of the comendites (Or₃₀–Or₄₆); both sets show only limited increase in Or outwards, and the zoning is greatest in quartz-bearing assemblages. The feldspar microlites in the residual glasses are invariably more potassic (2–4% Or) than their associated phenocrysts. In pantellerites the feldspars become more potassic as the residual liquids become more sodic; thus the most potassic feldspar is found in the most sodic (and peralkaline) pantellerite.Of the ferromagnesian phenocrysts, aenigmatite is the most ubiquitous and is commonly associated with hedenbergite±fayalite, or ferrorichterite; in the later stages of crystallization (groundmass), it is associated with acmite, arfvedsonite and tuhualite. Aside from slight variation in Ti/Fe+Ti ratio, aenigmatite is virtually constant in composition. The pyroxenes from the different assemblages have zones which together almost span the range acmitehedenbergite. Both ferrorichterite and arfvedsonite incorporate F but not Cl, and are slightly potassic. Tuhualite exists as two varieties; one blue and potassic, the other violet and sodic; both varieties reject halogens. Using (estimated) free-energy data, a field in fo₂, T space is postulated in which Fe-Ti oxides are absent; their place is taken by pyroxene and aenigmatite. The no-oxide field will be intercepted by a cooling liquid in which peralkalinity is increasing and in which fo₂ is near but above the FMQ buffer.The characteristic pattern of trace-elements in peralkaline volcanics (e.g., high Nb, Ta, Zr, Mo, Zn, Cd, R.E, etc; low Sr, Ba, Mg) are considered to be as much evidence for the peralkaline (salic) condition as of the genetic process. Several lines of evidence suggest that at liquidus temperatures, peralkaline rhyolites are essentially anhydrous.     

RAMS 2001: Current status and future directions

Summary ?An overview of the Regional Atmospheric Modeling System (RAMS) is presented. We focus on new developments in the RAMS physics and computational algorithms since 1992. We also summarize some of the recent applications of RAMS that includes synoptic-scale weather systems and climate studies, to small-scale research using RAMS configured as a large eddy simulation model or to even flow around urban buildings. The applications include basic research on clouds, cloud systems, and storms, examination of interactions between tropical deep convective systems and ocean circulations, simulations of tropical cyclones, extreme precipitation estimation, regional climatic studies of the interactions between the atmosphere and the biosphere or snow-covered land-surfaces, prototype realtime mesoscale numerical weather prediction, air pollution applications, and airflow around buildings. Received March 12, 2001; revised August 28, 2001     

Studies of the prominence-corona transition zone from rocket ultraviolet spectra of the March 1970 eclipse

Slitless VUV spectra of the eclipsed Sun were obtained from a rocket experiment for the first time during the 1970 eclipse. The spatially resolved spectra of a quiescent prominence in the wavelength range 900 Å–2200 Å consist of emission lines from ions formed in the temperature range 3.5 × 10⁴k–3.2 × 10⁵k. The spectral intensities have been interpreted in terms of physical parameters which indicate a transition zone of shell-like layers, the inner the cooler and thinner, the outer the hotter and more extended. The transition zone is about 3 km thick for a model thread of 2000 km in diameter.     

THE LOCATION OF METEORITE IMPACTS BY SEISMIC METHODS

Photographic methods for the location of meteorite falls are restricted to hours of darkness and limited by weather conditions, resulting in a low detection rate. The importance of rapid recovery of newly-fallen meteorites leads to the consideration of seismic methods for the location of impact points. The purpose of this paper is to discuss the degree to which seismic networks can augment the detection of meteorites by conventional means. Factors involved in the generation of seismic waves are considered. The present sophistication of experimental and computational techniques in seismology should enable a microearthquake detection network to locate within 2 km the impacts of larger meteorites. The detection limits are determined by meteorite size and the configuration and instrumentation of the seismograph network.     

Workshop on Indices and Indicators for Climate Extremes: Asheville, NC, USA, 3–6 June 1997 Breakout Group B: Precipitation

A uniform, international reference system of precipitation indices would greatly facilitate assessment of changes in global precipitation patterns, intensities and extremes. However, national/regional differences in precipitation monitoring standards, data quality control procedures, and product development practices complicate efforts to develop such a system. This report represents the results of Working Group B's concerted effort to examine in detail the problems associated with the development of the needed indicators and the Group's recommendations to address the identified issues. The Group concluded that a successful strategy must define a minimum set of indices/indicators based on higher quality data that would represent a global base set. The Group identified a set of indices for this purpose. This base data set should be complemented where possible by countries/regions having the data sets and processing resources to do more.     

Perfect fractionation in multicomponent, multiphase systems

Perfect fractionation models help infer the conditions under which molten rock material travels from the planet’s interior to the Earth’s surface where it cools and crystallizes. Quantitative models of melt crystallization, perfect fractionation paths through P–T-composition space, return calculated values of predicted quantities that can be compared to glass, rock, and mineral compositions measured in lava flows. Perfect fractionation models are based on thermodynamics and material balance constraints. Linear combinations of chemical potentials define equilibrium positions. The composition of the melt follows a path directly away from the composition of the phases at saturation, a material balance criterion. The number of adjustable parameters in a perfect fraction model is limited to two by Duhem’s theorem. Perfect fractionation models with one or two phases at saturation require only one mole fraction and one adjustable parameter be specified to calculate the fractionation path. The temperature and compositions of the saturating phases are determined by the equilibrium equations for one- or two-phase saturation in a melt of known compositions. With three or more phases at saturation, the composition of the melt has to be adjusted in the general case. Fractionation paths can also be inferred from a sequence of thermodynamic states calculated by minimizing a thermodynamic potential. The minimization procedure produces a fraction path that is conceptually different from the perfect fractionation path. Perfect fractionation models can be constructed to conserve a particular thermodynamic potential or variable such as enthalpy or density.     

Heat effects of assimilation,crystallization, and vesiculation in magmas

The heat balance for crystal fractionation and assimilation processes is the enthalpy difference between the initial and final states of a system. To order the calculations, the process is viewed as one of assimilation; the heat change for a crystallization process is obtained by changing the signs of the pertinent heat effects. The initial state is a mineral assemblage at T _s and P and an initial magma at T _m and P. The final state is a magma at T _m and P.The net heat change results from: (a) Unmixing of solid solutions, (b) Heating (cooling) each component to its fusion temperature, (c) Fusion of each component, (d) Cooling (heating) of each fused component to the magma temperature, (e) Mixing of each fused component in succession with the melt.The heat required to form a basaltic melt from its equilibrium mineral assemblage is approximately twice that required for a granitic melt. A zero heat balance, with the heat of crystallization from phases with which the magma is saturated supplying the energy for assimilation, necessitates that the mass crystallized be approximately twice that assimilated. The heat effects attendant on release of H₂O from silicic melts depends on the state of the H₂O in the external environment; a low fugacity could cause the magma to cool.The uncertainties in the calculations are estimated at ±10%.