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Forests are expected to expand into alpine areas because of climate warming, causing land-cover change and fragmentation of alpine habitats. However, this expansion will only occur if the present upper treeline is limited by low-growing season temperatures that reduce plant growth. This temperature limitation has not been quantified at a landscape scale. Here, we show that temperature alone cannot realistically explain high-elevation tree cover over a >100-km 2 area in the Canadian Rockies and that geologic/geomorphic processes are fundamental to understanding the heterogeneous landscape distribution of trees. Furthermore, upslope tree advance in a warmer scenario will be severely limited by availability of sites with adequate geomorphic/topographic characteristics. Our results imply that landscape-to-regional scale projections of warming-induced, high-elevation forest advance into alpine areas should not be based solely on temperature-sensitive, site-specific upper-treeline studies but also on geomorphic processes that control tree occurrence at long (centuries/millennia) timescales.

Abstract Oils that are potential candidates for in situ combustion recovery processes are often screened by means of their oxidation characteristics: in particular, the kinetics of the ignition process and the transition from low-temperature to high-temperature oxidation through what is known as the "negative temperature gradient region". These characteristics are readily studied in ramped-temperature oxidation tests, which involve the controlled heating of recombined, oil-saturated cores in a one-dimensional plug flow reactor under a flowing stream of air (or oxygen-containing gas). The purpose of these tests is to study the global oxidation behavior and reaction kinetics under controlled conditions, with the end purpose of providing realistic data for incorporation into a numerical simulator which can he used to predict field performance. A ramped-temperature oxidation apparatus was used to conduct a detailed, two-year parametric study of the oxidation characteristics of Athabasca Oil Sands bitumen. The test matrix involved various levels of pressure gas injection rate, oxygen content of the injected gas and maximum ramp temperature. This paper details the principal findings for the 45-test study: in particular, the need to maintain high reaction temperatures >380 C) in order to mobilize and produce heavy oils under conditions of dry in situ combustion. Design considerations and operational guidelines for successful field projects which can be suggested from the results of this study are also discussed. Introduction In order to successfully exploit the vast potential of processes based on the injection of air or an oxygen-containing gas for the recovery of conventional and heavy oils, it is necessary to understand the nature of the oxidation reactions which are involved. The traditional concept of in situ combustion, which is based on the high-temperature combustion of a coke-like fuel, will not explain the combustion behavior which is observed in many field projects or even in laboratory combustion tube experiments. For this reason, a number of experiments have been developed which concentrate on the global oxidation kinetics. These studies normally involve exposing the crude oil to a programmed rate of heating while in contact with the oxidizing gas. The oxidation kinetics are then observed using effluent gas analysis techniques, and differential thermal techniques such as the differential thermal analysis (DTA) work of Vossoughi et al., the pressurized differential scanning calorimetry (PDSC) studies of Phillips et al., and Belkharchouche and Hughes and the accelerating rate calorimetry (ARC) technique of Yannimaras et al. Previous investigations of the oxidation reactions which occur during in situ combustion processes have shown the existence of at least two temperature ranges over which the oxygen uptake rates are significant. While Kisler and Shallcross have reported that the light (40.2 API) Australian oil which they studied exhibited at least three temperature ranges over which localized maxima in the oxygen uptake rate were observed, the majority of heavy oils for which oxidation data have been reported exhibit only two distinct local maxima in the oxidation rates. For convenience, the two temperature ranges where elevated oxygen uptake or energy generation rates are observed are denoted as the low-temperature oxidation and high-temperature combustion regions. For heavy oils, the range of temperatures associated with the low-temperature oxidation region is roughly from 150 to 300 C, while the high-temperature combustion region generally corresponds to reaction temperatures in the range from 380 to 800 C. The transition temperature range which falls between the temperatures corresponding to the low-temperature oxidation and high-temperature combustion regions is characterized by reduced oxygen uptake and energy generation rates. The lower temperature portion of this transition range in which the oxygen uptake and energy generation rates decrease with increasing temperature is the "negative temperature gradient region". The significance of this region will be more fully explored in the following sections of this paper. Description of Test Procedure Equipment The ramped-temperature oxidation apparatus and test procedures have been described in detail by Moore et al. The apparatus essentially consisted of a plug flow reactor with an inside diameter of 22.1 mm and an inside length of 320.7 mm. The reactor was equipped with five Inconel-sheathed Type K thermocouples which were spaced 50.8 mm apart and inserted radially to the centerline of the core. The reactor was mounted in an aluminum beating block which was equipped with strap heaters. Temperature control and monitoring were achieved using an in-house developed computer-based system. A mass-flow meter controlled the oxidizing gas injection rate and a backpressure control valve maintained the desired operating pressure at the reactor outlet.

National environmental protection through law is a relatively recent initiative. The written national constitutions of federal countries, such as Canada, did not originally provide for which level of government would enjoy the primary constitutional authority to regulate for environmental protection. Today, a legal jurisdiction must be interpreted and declared from an old imperial document that did not foresee the environment as a discrete subject for regulation. This article describes the experience of how each of two exclusively sovereign levels of government in the same country, the courts and the constitution have combined over the last half century to establish a unique regime of environmental protection in Canada, and how that regime continues to be developed.

The life cycle Greenhouse Gas (GHG) emissions associated with the production and use of transportation fuels from conventional and unconventional fossil fuel sources in Canada and the USA are investigated. The studied pathways include reformulated gasoline and low sulphur diesel produced from oil sands, oil shale, coal and natural gas, as well as reference pathways from conventional crude oil. A comparison of Life Cycle Assessments (LCAs) completed for these fuels indicates considerable uncertainty in these emissions, illustrating the need for further LCAs with particular attention to completeness and transparency. Based on the considered studies, only one unconventional pathway has better GHG emissions performance than the conventional pathways: Fischer-Tropsch diesel from natural gas. However, the limitations of the data used here and other factors that may restrict a switch to natural gas must be considered. Furthermore, there are considerable opportunities to reduce emissions from the unconventional pathways.

Abstract This study presents the comparison of the life cycle performance of two different urban energy systems, applied to a large mixed-use community, in Calgary (Canada). The two systems investigated consist of an energy efficient conventional system, using heat pumps for heating, cooling and domestic hot water; the second design widely deploys solar thermal panels coupled to district heating infrastructure and a borehole seasonal thermal storage. The analysis is based on the Life Cycle Assessment methodology and includes the stages of raw materials and energy supply, system manufacturing, use stage of the systems, generation and use of energy on-site, maintenance and components’ substitution, and explores the performances of the systems on a life cycle perspective thanks to the use of different indicators of ILCD 2011 Midpoint impact assessment method. The solar-based system, performs better than the conventional system from the point of view of all indicators used in the study. In detail, ozone depletion and land use can be reduced of about 79.7% and 27% respectively, while the remaining impact categories show a reduction of about 39–56%. These results can be extended to other similar systems operating under similar weather constraints, energy systems included in the operation, thermal loads requirements. Moreover, the study is based on the premises and assumptions of real documented case studies in Canada, thus further reinforcing the solidity of the results.

AbstractOver the last few decades, research on the abatement of carbon dioxide (CO2) gas has gained momentum, due to its increasing atmospheric levels. This study investigated high‐temperature steam‐only gasification of woody biomass for the production of high‐purity hydrogen integrated with CO2 capture in a moving‐bed gasifier. Extensive process modelling and simulation were performed using the superior solid handling features of the Aspen Plus process simulator software. After validating the model with experimental data from a demonstration plant available in the open literature, a reversible carbonation‐calcination reaction of calcium oxide (CaO) with CO2 was added to the system. Sensitivity analyses were conducted to verify the predictive accuracy of the model. The effects of steam‐to‐carbon (S/C) ratio on the resulting gas composition were thoroughly studied to delineate the complex process of gasification. Beyond the mitigation of CO2 emissions, the introduction of a CaO‐based sorbent in the process simulation significantly enhanced hydrogen production by simultaneously promoting the forward water‐gas shift reaction and reducing tars through increased tar‐cracking reactions. The results show that hydrogen of a higher purity was produced with the inclusion of dry‐sorption CO2 capture in the gasification process. Moreover, the addition of the sorbent increased the higher heating values (HHV) by 3 times and improved the cold gas efficiency by 34 %.

Bradshaw et al. (2021) make a call to action in light of three major crises—biodiversity loss, the sixth mass extinction, and climate disruption. We have no contention with Bradshaw et al.’s diagnosis of the severity of the crises. Yet, their call for scientists to “tell it like it is,” their appeal to political “leaders,” and the great attention they afford to human population growth as a main driver underpinning the three crises, rest on contested assumptions about the role of science in societal transformations, and are scientifically flawed and politically problematic. In this commentary, we challenge Bradshaw et al.’s assumptions concerning the nature of science, polity, and humanity as well as the implicit politics underlying their analysis and messaging. We end with an alternative call to action.

Aerobic granules, a relative novel form of microbial aggregate, are capable of degrading many toxic organic pollutants. Appropriate strategy is needed to acclimate seed sludge to the toxic compounds for successful granulation. In this study, two distinct strategies, i.e. mixed or single carbon sources, were experimented to obtain phenol-acclimated sludge. Their effects on reactor performance, biomass characteristics, microbial population and the granulation process were analyzed. Sludge fed with phenol alone exhibited faster acclimation and earlier appearance of granules, but possibly lower microbial diversity and reactor stability. Using a mixture of acetate and phenol in the acclimation stage, on the other hand, led to a reactor with slower phenol degradation and granulation, but eventual formation of strong and stable aerobic granules. In addition, the content of intracellular polyhydoxyakanoates (PHA) was also monitored, and significant accumulation was observed during the pre-granulation stage, where PHA >50% of dry weight was observed in both reactors.