67 research outputs found
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How has climate responded to natural perturbations?
No full textIn this chapter, we describe and explain some of the patterns observed in the behaviour of Earth’s climate system. We explain some of the causes of the climate’s natural variability, setting contemporary climate change in its longer-term context. We describe the various lines of evidence about climate forcing and the feedbacks that determine the responses to perturbations, and the way in which reconstructions of past climates can be used in combination with models and contemporary observations of change
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Land-ocean atmosphere interactions and monsoon climate change: a paleo-perspective
No full textTowards a unified theory of plant photosynthesis and hydraulics
No full textThe global carbon and water cycles are strongly governed by the simultaneous diffusion of CO2 and water vapour through the leaves of terrestrial plants. These diffusive fluxes are controlled by plants’ adaptations to balance carbon gains and hydraulic risks. We introduce a trait-based optimality theory that unifies the treatment of stomatal responses and biochemical acclimation of plants to changing environments. Tested with experimental data from eighteen species, our model successfully predicts the simultaneous decline in carbon assimilation rate, stomatal conductance, and photosynthetic capacity during progressive soil drought. It also correctly predicts the dependencies of gas exchange on atmospheric vapour pressure deficit, temperature, and CO2. Consistent with widely observed patterns, inferred trait values for the analysed species display a spectrum of stomatal strategies, a safety-efficiency trade-off, and a convergence towards low hydraulic safety margins. Our unifying theory opens new avenues for reliably modelling the interactive effects of drying soil and air and rising atmospheric CO2 on global photosynthesis and transpiration
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The influence of vegetation, fire spread and fire behaviour on biomass burning and trace gas emissions: results from a process-based model
No full textA process-based fire regime model (SPITFIRE) has been developed, coupled with ecosystem dynamics in the LPJ Dynamic Global Vegetation Model, and used to explore fire regimes and the current impact of fire on the terrestrial carbon cycle and associated emissions of trace atmospheric constituents. The model estimates an average release of 2.24 Pg C yr<sup>−1</sup> as CO<sub>2</sub> from biomass burning during the 1980s and 1990s. Comparison with observed active fire counts shows that the model reproduces where fire occurs and can mimic broad geographic patterns in the peak fire season, although the predicted peak is 1–2 months late in some regions. Modelled fire season length is generally overestimated by about one month, but shows a realistic pattern of differences among biomes. Comparisons with remotely sensed burnt-area products indicate that the model reproduces broad geographic patterns of annual fractional burnt area over most regions, including the boreal forest, although interannual variability in the boreal zone is underestimated
The Maghreb states : regional and foreign policies 1973-1987
No full textBy 1973, the period of uncertainty that followed
independence in the Maghreb was over, and the regimes in place -
whether civilian or military were there to remain. Legitimising
formulas were no longer rested on the ideological rhetoric that had
been derived from the euphoria of independence, and by now the
Maghrebi elites had to seek other legitimising sources. Thus they
embarked on consolidating the state through institutionalisation and
through new policies that sought to associate key constituencies with
the conduct of the government. The intense social transformation
over the last two decades, with greater access to education, has been
coupled with the new emphasis on the state. Ideology has retreated
before the advance of pragmatism and a greater awareness of the
developments both at home and abroad. Accordingly, our work suggests
that foreign policies of the Maghreb States, in the period under study
have been executed in accordance with, and in response to, the
exigencies of 'national interest'.
The thesis is divided into five parts:
The First Part, discusses different theories of foreign policy-making
and sets out our suggested framework for analysis;
The Second Part, deals with the conflicting and competitive nature
that commands Inter-Maghrebin relations. The strife and rivalry for
leadership and supremacy in North Africa has been a crucial factor
dictating Maghrebi policies in Africa, the Middle East, Europe and
beyond;
The Third Part, treats Maghrebi relations with the Arab World and
their attitudes with regard to issues ranging from the Arab Israeli
conflict to the Iran-Iraq War, while competing for support and allies
in their inter-Maghrebin altercations;
Part Four, is concerned with the Maghrebi African policies. While the
continent became a battle ground for the struggle against Isreal, it
has also become a forum that for long has been dominated by
inter-Maghrebin rivalries;
Finally, the Fifth Part, deals with the Maghrebi foreign policies with
regard to Europe and the super powers. As in the case of their
relations with the Middle East and Africa, relations with Europe and
the super powers have also been conflicting and competitive as far as
the Maghreb states are concerned. Here, however, Maghrebi pragmatic
approach has prevailed through the divorce of the foreign policy
utterances from economic practices
Multiple greenhouse-gas feedbacks from the land biosphere under future climate change scenarios
No full textAtmospheric concentrations of the three important greenhouse gases (GHGs) CO2, CH4 and N2O are mediated by processes in the terrestrial biosphere that are sensitive to climate and CO2. This leads to feedbacks between climate and land and has contributed to the sharp rise in atmospheric GHG concentrations since pre-industrial times. Here, we apply a process-based model to reproduce the historical atmospheric N2O and CH4 budgets within their uncertainties and apply future scenarios for climate, land-use change and reactive nitrogen (Nr) inputs to investigate future GHG emissions and their feedbacks with climate in a consistent and comprehensive framework1. Results suggest that in a business-as-usual scenario, terrestrial N2O and CH4 emissions increase by 80 and 45%, respectively, and the land becomes a net source of C by AD 2100. N2O and CH4 feedbacks imply an additional warming of 0.4–0.5 °C by AD 2300; on top of 0.8–1.0 °C caused by terrestrial carbon cycle and Albedo feedbacks. The land biosphere represents an increasingly positive feedback to anthropogenic climate change and amplifies equilibrium climate sensitivity by 22–27%. Strong mitigation limits the increase of terrestrial GHG emissions and prevents the land biosphere from acting as an increasingly strong amplifier to anthropogenic climate change
On the cause of abrupt vegetation in North Africa during the Holocene: Climate variability vs. vegetation feedback
No full textThe abrupt desertification over the northern Africa in the mid-Holocene is studied in both a complex and a simple coupled climate-vegetation model. In contrast to the previous mechanism that relies on strong positive vegetation-climate feedback and the resulted multiple equilibria, we propose a new mechanism in which the abrupt desertification is caused by low frequency climate variability, rather than a positive vegetation-climate feedback. The implication of this new mechanism to modelling and observation is also discussed
Ergonomia cognitiva e a interação pessoa-computador: análise da usabilidade da urna eletrônica 2002 e do módulo impressor externo
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia de Produção.Transformar o trabalho e as condições em que este é realizado, visando adaptá-lo às características e às necessidades de quem o executa, constituem os principais objetivos da ergonomia. Desta forma, a análise da URNA ELETRÔNICA segundo o referencial teórico e metodológico desta disciplina diagnostica sua usabilidade e eficácia, ao identificar as estratégias operatórias empregadas pelos eleitores e as dificuldades que estes enfrentam durante a interação
Towards a unified theory of plant photosynthesis and hydraulics
No full textThe global carbon and water cycles are strongly governed by the simultaneous diffusion of CO2 and water vapour through the leaves of terrestrial plants. These diffusive fluxes are controlled by plants’ adaptations to balance carbon gains and hydraulic risks. We introduce a trait-based optimality theory that unifies the treatment of stomatal responses and biochemical acclimation of plants to changing environments. Tested with experimental data from eighteen species, our model successfully predicts the simultaneous decline in carbon assimilation rate, stomatal conductance, and photosynthetic capacity during progressive soil drought. It also correctly predicts the dependencies of gas exchange on atmospheric vapour pressure deficit, temperature, and CO2. Consistent with widely observed patterns, inferred trait values for the analysed species display a spectrum of stomatal strategies, a safety-efficiency trade-off, and a convergence towards low hydraulic safety margins. Our unifying theory opens new avenues for reliably modelling the interactive effects of drying soil and air and rising atmospheric CO2 on global photosynthesis and transpiration
Pedogenesis on the Sefton Coastal Dunes, NW England
No full textA thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of PhilosophyThis work examines the use of pedo-properties to identify dune soil system responses to environmental change on the Sefton coast, based on the development of conceptual pedogenic models. Previous environmental change and shoreline dynamics are determined through O.S. maps and aerial photographs, while present day processes are investigated through a dune-toe photographic survey and seasonal monitoring by fixed point photography. Topsoil (0-5 cm) physico-chemical characteristics are presented in a series of baseline GIS maps, displaying spatial pedo-property variation across the dune landscape. Combined with vegetation data, topsoil analysis identifies 10 distinct pedo-environments. Physico-chemical characteristics of associated National Soil Resources Institute (NSRI) soil profile classifications and an exposed stratigraphic section are presented graphically in a proposed sequence of development. Topsoil and soil profile samples are analysed for soil pH, soil organic matter (SOM) content, particle size, geochemical composition and mineral magnetism. Significant differences (p <0.05) are apparent for the suite of topsoil characteristics collated, indicating discrete dune environments are influenced by specific soil properties. Distinct down-profile variations in soil characteristics are also apparent between dune environments, highlighting pedological dynamism. Multivariate Factor analysis groups bare sand and mobile dune communities into ‘frontal dunes’ and fixed dune community, pasture, scrub, deciduous woodland and coniferous plantations into ‘hind dunes’, separating these topsoil environments from heath and slack communities. Factor analysis also identifies linkages between pedo-characteristics within soil profile horizons, suggesting pedogenesis on the Sefton dunes initiates as raw sand, progressing to sand-pararendzinas through leaching of nutrients. Desalinization and decalcification processes lead to brown earth development, followed by increased acidicification, subsequently, resulting in micro-podzol formation. Groundwater gley soils are associated with dune slacks, where drainage is inhibited and anaerobic conditions prevail. Analysis of buried soils suggests such pedo-environment formations are cyclic, responding to phases of shoreline regression/transgression, dune activity and stabilization. Conceptual models are designed to graphically demonstrate pedogenesis under both erosion and deposition regimes on the Sefton coast. Regression equations and correlation coefficients between pedo-properties and distance from mean high water are used as a proxy for soil age, which represent lateral soil maturity from the unstable frontal dunes to the stable hind dunes inland. The models simulate formation and process of the full array of soil properties, accounting for geomorphological impacts and anthropogenic influences. This has great implications for dune managers by raising awareness of pedogenesis as an integral part of nature and associated habitats, which could be incorporated in future shoreline management plans (SMPs)
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