Transport of water in frozen soil IV. Analysis of experimental results on the effects of ice content

Effects of ice content on the transport of water in frozen soil are studied experimentally and theoretically under isothermal conditions. A physical law, that the flux of water in unsaturated frozen soil is proportional to the gradient of total water content is proposed. Theoretical justification is made by the use of the two-phase flow theory. The experimental results are shown to support the proposed physical law. The results of this study are presented in two parts and this is the second paper describing the theoretical aspects of the study.     

Weathering of sulfidic shale and copper mine waste: secondary minerals and metal cycling in Great Smoky Mountains National Park,Tennessee, and North Carolina,USA

Metal cycling via physical and chemical weathering of discrete sources (copper mines) and regional (non-point) sources (sulfide-rich shale) is evaluated by examining the mineralogy and chemistry of weathering products in Great Smoky Mountains National Park, Tennessee, and North Carolina, USA. The elements in copper mine waste, secondary minerals, stream sediments, and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum, copper, zinc, and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments. Acid-mine drainage has not developed in streams draining inactive copper mines. Acid-rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid-mine drainage elsewhere. Despite the high rainfall in the mountain range, sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems.Electronic Supplementary Material  Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.

Microwave observations of daily Antarctic sea-ice edge expansion and contraction rates

Algorithms for estimating sea-ice extent from remotely sensed microwave sensor data can benefit from knowledge of the "a priori" distribution of the daily expansion and contraction of the sea-ice pack. To estimate the probability distribution of daily Antarctic sea-ice extent change, two independent sea-ice datasets are analyzed: sea-ice extent derived from the QuikSCAT scatterometer and ice concentration estimates from the Special Sensor Microwave/Imager. The daily sea-ice advance and retreat is tracked over a four-year period. The distribution of the daily sea-ice advance/retreat from each sensor is similar and is approximately double-exponential. Daily ice-pack statistics are presented.     

Quantifying anthropogenic influence on recent near-surface temperature change

We assess the extent to which observed large-scale changes in near-surface temperatures over the latter half of the twentieth century can be attributed to anthropogenic climate change as simulated by a range of climate models. The hypothesis that observed changes are entirely due to internal climate variability is rejected at a high confidence level independent of the climate model used to simulate either the anthropogenic signal or the internal variability. Where the relevant simulations are available, we also consider the alternative hypothesis that observed changes are due entirely to natural external influences, including solar variability and explosive volcanic activity. We allow for the possibility that feedback processes, other than those simulated by the models considered, may be amplifying the observed response to these natural influences by an unknown amount. Even allowing for this possibility, the hypothesis of no anthropogenic influence can be rejected at the 5% level in almost all cases. The influence of anthropogenic greenhouse gases emerges as a substantial contributor to recent observed climate change, with the estimated trend attributable to greenhouse forcing similar in magnitude to the total observed warming over the 20th century. Much greater uncertainty remains in the response to other external influences on climate, particularly the response to anthropogenic sulphate aerosols and to solar and volcanic forcing. Our results remain dependent on model-simulated signal patterns and internal variability, and would benefit considerably from a wider range of simulations, particularly of the responses to natural external forcing.     

Shifts in the synoptic systems influencing southwest Western Australia

A self-organising map is used to classify the winter circulation affecting southwest Western Australia (SWWA) into 20 different synoptic types. The changes in the frequency of these types and their links to observed rainfall are analysed to further understand the significant, prolonged, rainfall drop observed in this region since 1975. The temporal variability of the different synoptic types link well with the observed rainfall changes. The frequency of the troughs associated with wet conditions across SWWA has declined markedly since 1975 while the frequency of the synoptic types with high pressure over the continent, associated with dry conditions, has increased. Combining the frequency of the synoptic systems with the amount of observed rainfall allows a quantitative analysis of the rainfall decline. The decreased frequency of the troughs associated with very wet conditions accounts for half of the decline. Reductions in the amount of rainfall precipitating from each system also contribute to the decline. Large-scale circulation changes, including increases in the mean sea-level pressure and a decrease in the general baroclinicity of the region have been associated with the rainfall decline. These changes are suggested to be linked to increasing levels of greenhouse gases. Due to the strong link between the number of trough types and the rainfall over SWWA, the shifts in the frequency of these synoptic types could be used as a tool to assess simulated rainfall changes, particularly into the future.     

Flow Over Hills with Variable Roughness

The effect of variable roughness length upon the flow characteristics over hills is investigated. The changes considered herein cover a range of flow configurations such as the change from a forested (rough) valley with a moderately smooth hilltop to a grassy valley (smooth) with a “spiky” (rough) mountain top. The effect of moving the roughness with respect to the hill is also considered. Although many of the flow features change when the position of the roughness change is varied with respect to the hill these changes have very little impact upon the global properties used within orographic drag parametrization schemes.     

Some economics of ‘dangerous’ climate change: Reflections on the Stern Review

The Stern Review on the Economics of Climate Change concluded that there can be “no doubt” the economic risks of business-as-usual (BAU) climate change are “very severe” [Stern, 2006. The Economics of Climate Change. HM Treasury, London, p. 188]. The total cost of climate change was estimated to be equivalent to a one-off, permanent 5–20% loss in global mean per-capita consumption today. And the marginal damage cost of a tonne of carbon emitted today was estimated to be around $312 [p. 344]. Both of these estimates are higher than most reported in the previous literature. Subsequently, a number of critiques have appeared, arguing that discounting is the principal explanation for this discrepancy. Discounting is important, but in this paper we emphasise that how one approaches the economics of risk and uncertainty, and how one attempts to model the very closely related issue of low-probability/high-damage scenarios (which we connect to the recent discussion of ‘dangerous’ climate change), can matter just as much. We demonstrate these arguments empirically, using the same models applied in the Stern Review. Together, the issues of risk and uncertainty on the one hand, and ‘dangerous’ climate change on the other, raise very strongly questions about the limits of a welfare-economic approach, where the loss of natural capital might be irreversible and impossible to compensate. Thus we also critically reflect on the state-of-the-art in integrated assessment modelling. There will always be an imperative to carry out integrated assessment modelling, bringing together scientific ‘fact’ and value judgement systematically. But we agree with those cautioning against a literal interpretation of current estimates. Ironically, the Stern Review is one of those voices. A fixation with cost-benefit analysis misses the point that arguments for stabilisation should, and are, built on broader foundations.