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Summary for Policy Makers
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- By Thomas B. Johansson, Lund University, Nebojsa Nakicenovic, International Institute for Applied Systems Analysis and Vienna University of Technology, Anand Patwardhan, Indian Institute of Technology-Bombay), Luis Gomez-Echeverri, International Institute for Applied Systems Analysis, Rangan Banerjee, Indian Institute of Technology, Sally M. Benson, Stanford University, Daniel H. Bouille, Bariloche Foundation, Abeeku Brew-Hammond, Kwame Nkrumah University of Science and Technology, Aleh Cherp, Central European University, Suani T. Coelho, National Reference Center on Biomass, University of São Paulo, Lisa Emberson, Stockholm Environment Institute, University of York, Maria Josefina Figueroa, Technical University, Arnulf Grubler, International Institute for Applied Systems Analysis, Austria and Yale University, Kebin He, Tsinghua University, Mark Jaccard, Simon Fraser University, Suzana Kahn Ribeiro, Federal University of Rio de Janeiro, Stephen Karekezi, AFREPREN/FWD, Eric D. Larson, Princeton University and Climate Central, Zheng Li, Tsinghua University, Susan McDade, United Nations Development Programme), Lynn K. Mytelka, United Nations University-MERIT, Shonali Pachauri, International Institute for Applied Systems Analysis, Keywan Riahi, International Institute for Applied Systems Analysis, Johan Rockström, Stockholm Environment Institute, Stockholm University, Hans-Holger Rogner, International Atomic Energy Agency, Joyashree Roy, Jadavpur University, Robert N. Schock, World Energy Council, UK and Center for Global Security Research, Ralph Sims, Massey University, Kirk R. Smith, University of California, Wim C. Turkenburg, Utrecht University, Diana Ürge-Vorsatz, Central European University, Frank von Hippel, Princeton University, Kurt Yeager, Electric Power Research Institute and Galvin Electricity Initiative
- Global Energy Assessment Writing Team
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- Book:
- Global Energy Assessment
- Published online:
- 05 September 2012
- Print publication:
- 27 August 2012, pp 3-30
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Summary
Introduction
Energy is essential for human development and energy systems are a crucial entry point for addressing the most pressing global challenges of the 21st century, including sustainable economic and social development, poverty eradication, adequate food production and food security, health for all, climate protection, conservation of ecosystems, peace and security. Yet, more than a decade into the 21st century, current energy systems do not meet these challenges.
A major transformation is therefore required to address these challenges and to avoid potentially catastrophic future consequences for human and planetary systems. The Global Energy Assessment (GEA) demonstrates that energy system change is the key for addressing and resolving these challenges. The GEA identifies strategies that could help resolve the multiple challenges simultaneously and bring multiple benefits. Their successful implementation requires determined, sustained and immediate action.
Transformative change in the energy system may not be internally generated; due to institutional inertia, incumbency and lack of capacity and agility of existing organizations to respond effectively to changing conditions. In such situations clear and consistent external policy signals may be required to initiate and sustain the transformative change needed to meet the sustainability challenges of the 21st century.
The industrial revolution catapulted humanity onto an explosive development path, whereby, reliance on muscle power and traditional biomass was replaced mostly by fossil fuels. In 2005, some 78% of global energy was based on fossil energy sources that provided abundant and ever cheaper energy services to more than half the people in the world.
Technical Summary
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- By Thomas B. Johansson, Lund University, Nebojsa Nakicenovic, International Institute for Applied Systems Analysis and Vienna University of Technology, Anand Patwardhan, Indian Institute of Technology, Luis Gomez-Echeverri, International Institute for Applied Systems Analysis, Doug J. Arent, National Renewable Energy Laboratory, Rangan Banerjee, Indian Institute of Technology, Sally M. Benson, Stanford University, Daniel H. Bouille, Bariloche Foundation, Abeeku Brew-Hammond, Kwame Nkrumah University of Science and Technology, Aleh Cherp, Central European University, Suani T. Coelho, National Reference Center on Biomass, University of São Paulo, Lisa Emberson, Stockholm Environment Institute, University of York, Maria Josefina Figueroa, Technical University, Arnulf Grubler, International Institute for Applied Systems Analysis, Austria and Yale University, Kebin He, Tsinghua University, Mark Jaccard, Simon Fraser University, Suzana Kahn Ribeiro, Federal University of Rio de Janeiro, Stephen Karekezi, AFREPREN/FWD, Eric D. Larson, Princeton University and Climate Central, Zheng Li, Tsinghua University, Susan McDade, United Nations Development Programme, Lynn K. Mytelka, United Nations University-MERIT, Shonali Pachauri, International Institute for Applied Systems Analysis, Keywan Riahi, International Institute for Applied Systems Analysis, Johan Rockström, Stockholm Environment Institute, Stockholm University, Hans-Holger Rogner, International Atomic Energy Agency, Joyashree Roy, Jadavpur University, Robert N. Schock, World Energy Council, UK and Center for Global Security Research, Ralph Sims, Massey University, Kirk R. Smith, University of California, Wim C. Turkenburg, Utrecht University, Diana Ürge-Vorsatz, Central European University, Frank von Hippel, Princeton University, Kurt Yeager, Electric Power Research Institute and Galvin Electricity Initiative
- Global Energy Assessment Writing Team
-
- Book:
- Global Energy Assessment
- Published online:
- 05 September 2012
- Print publication:
- 27 August 2012, pp 31-94
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Summary
Introduction
Energy is essential for human development and energy systems are a crucial entry point for addressing the most pressing global challenges of the 21st century, including sustainable economic, and social development, poverty eradication, adequate food production and food security, health for all, climate protection, conservation of ecosystems, peace, and security. Yet, more than a decade into the 21st century, current energy systems do not meet these challenges.
In this context, two considerations are important. The first is the capacity and agility of the players within the energy system to seize opportunities in response to these challenges. The second is the response capacity of the energy system itself, as the investments are long-term and tend to follow standard financial patterns, mainly avoiding risks and price instabilities. This traditional approach does not embrace the transformation needed to respond properly to the economic, environmental, and social sustainability challenges of the 21st century.
A major transformation is required to address these challenges and to avoid potentially catastrophic consequences for human and planetary systems. The GEA identifies strategies that could help resolve the multiple challenges simultaneously and bring multiple benefits. Their successful implementation requires determined, sustained, and immediate action.
The industrial revolution catapulted humanity onto an explosive development path, whereby reliance on muscle power and traditional biomass was replaced mostly by fossil fuels. In 2005, approximately 78% of global energy was based on fossil energy sources that provided abundant and ever cheaper energy services to more than half the world's population.
On weakly nonlinear convection in mushy layers during solidification of alloys
- B. S. OKHUYSEN, D. N. RIAHI
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- Journal:
- Journal of Fluid Mechanics / Volume 596 / 25 January 2008
- Published online by Cambridge University Press:
- 17 January 2008, pp. 143-167
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We consider the problem of weakly nonlinear buoyant convection in horizontal mushy layers with permeable mush–liquid interface during the solidification of binary alloys. We analyse the effects of several parameters of the problem on the stationary modes of convection in the form of either a hexagonal pattern or a non-hexagonal pattern such as rolls, rectangles and squares. No assumption is made on the thickness of the mushy layer, and a number of simplifying assumptions made in previous theoretical investigations of the problem are relaxed here in order to study the problem based on a more realistic model. Using both analytical and numerical methods, we determine the steady solutions for the nonlinear problem in a range of the Rayleigh number R near its critical value. Both the nonlinear basic state and variable permeability of the present problem favour hexagon-pattern convection. The results of the analyses and computations indicate that depending on the range of values of the parameters, bifurcation to hexagonal or non-hexagonal convection can be either supercritical or subcritical. However, among all the computed solutions in the particular range of values of the parameters that are most relevant to those of the experiments, only convection in the form of down-hexagons with downflow at the cell centres and upflow at the cell boundaries, was found to be realizable, in the sense that its amplitude increases with R.
Preferred pattern of convection in a porous layer with a spatially non-uniform boundary temperature
- D. N. Riahi
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- Journal:
- Journal of Fluid Mechanics / Volume 246 / January 1993
- Published online by Cambridge University Press:
- 26 April 2006, pp. 529-543
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The problem of finite-amplitude thermal convection in a porous layer between two horizontal walls with different mean temperatures is considered when spatially non-uniform temperature with amplitude L* is prescribed at the lower wall. The nonlinear problem of three-dimensional convection for values of the Rayleigh number close to the classical critical value is solved by using a perturbation technique. Two cases are considered: the wavelength γ(b)n of the nth mode of the modulation is equal to or not equal to the critical wavelength γc for the onset of classical convection. The preferred mode of convection is determined by a stability analysis in which arbitrary infinitesimal disturbances are superimposed on the steady solutions. The most surprising results for the case γ(b)n = γc for all n are that regular or non-regular solutions in the form of multi-modal pattern convection can become preferred in some range of L*, provided the wave vectors of such pattern are contained in the set of wave vectors representing the spatially non-uniform boundary temperature. There can be critical value(s) L*c of L* below which the preferred flow pattern is different from the one for L* > L*c. The most surprising result for the case γ(b)n ≠ γc and γ(b)n ≡ γ(b) for all n is that some three-dimensional solution in the form of multi-modal convection can be preferred, even if the boundary modulation is one-dimensional, provided that the wavelength of the modulation is not too small. Here γ(b) is a constant independent of n.
Modal package convection in a porous layer with boundary imperfections
- D. N. Riahi
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- Journal:
- Journal of Fluid Mechanics / Volume 318 / 10 July 1996
- Published online by Cambridge University Press:
- 26 April 2006, pp. 107-128
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Thermal convection with a continuous finite bandwidth of modes in a porous layer with horizontal walls at different mean temperatures is considered when a spatially non-uniform temperature is prescribed at the lower wall. The nonlinear problem of three-dimensional convection for values of the Rayleigh number close to the classical critical value is solved by using multiple scales and perturbation techniques. The preferred flow solutions are determined by a stability analysis. It is found that for the case of near-resonant wavelength excitation regular or non-regular solutions in the form of superposition of small-scale multi-modal solutions with large-scale multimodal (or non-modal) amplitude can become preferred, provided the wave vectors of the solutions are contained in the set of wave vectors due to the modal form of the boundary imperfections and the form of the large-scale part is the same as that due to the boundary imperfections. For the case of non-resonant wavelength excitation some three-dimensional solutions in the form of superposition of small-scale multi-modal solutions with large-scale multi-modal (or non-modal) amplitudes can be preferred, provided that the wavelength of the small-scale modulation is not too small. Large-scale flow structures are quite different from the small-scale flow structures in a number of cases and, in particular, they can exhibit kinks and can be non-modal in nature. The resulting flow patterns are affected accordingly, and they can provide quite unusual and non-regular three-dimensional preferred patterns. In particular, they are multiples of irregular rectangular patterns, and they can be non-periodic.
Nonlinear oscillatory convection in rotating mushy layers
- D. N. RIAHI
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- Journal:
- Journal of Fluid Mechanics / Volume 553 / 25 April 2006
- Published online by Cambridge University Press:
- 06 April 2006, pp. 389-400
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We consider the problem of nonlinear oscillatory convection in a horizontal mushy layer rotating about a vertical axis. Under a near-eutectic approximation and the limit of large far-field temperature, we determine the stable and unstable oscillatory solutions of the weakly nonlinear problem by using perturbation and stability analyses. It was found that depending on the values of the parameters, supercritical simple travelling modes of convection in the form of hexagons, squares, rectangles or rolls can become stable and preferred, provided the value of the rotation parameter $\tau$ is not too small and is below some value, which can depend on the other parameter values. Each supercritical form of the oscillatory convection becomes subcritical as $\tau$ increases beyond some value, and each subcritical form of the oscillatory convection is unstable. In contrast to the non-rotating case, qualitative properties of the left-travelling modes of convection are different from those of the right-travelling modes, and such qualitative difference is found to be due to the interactions between the local solid fraction and the Coriolis term in the momentum-Darcy equation.
On nonlinear convection in mushy layers. Part 2. Mixed oscillatory and stationary modes of convection
- D. N. RIAHI
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- Journal:
- Journal of Fluid Mechanics / Volume 517 / 25 September 2004
- Published online by Cambridge University Press:
- 11 October 2004, pp. 71-101
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This paper presents part 2 of a study of nonlinear convection in horizontal mushy layers during the solidification of binary alloys. Part 1 dealt with only the oscillatory modes of convection (Riahi, J. Fluid Mech. vol. 467, 2002, pp. 331–359). In the present paper we consider the particular range of parameters where the critical values of the scaled Rayleigh number $R$ for the onset of oscillatory and stationary convection are close to each other, and we develop and analyse a nonlinear theory in such a parameter regime which takes into account those mixed stationary and oscillatory modes of convection with common wavenumber vectors. Under a near-eutectic approximation and in the limit of large far-field temperature, we first determine a number of weakly nonlinear solutions, and then the stability of these solutions is investigated. The most interesting result is the preference for a mixed solution composed of standing and stationary hexagonal modes over a relatively wide range of the parameter values and for $R$ just above its lowest subcritical value where convection is possible. Such a preferred solution has properties mostly in agreement with the experimental results due to Tait et al. (Nature, vol. 359, 1992, pp. 406–408) in the sense that the flow is downward at the cell centres, upward at the cell boundaries and there is some tendency for channel formation at the cell nodes.
Nonlinear steady convection in rotating mushy layers
- D. N. RIAHI
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- Journal:
- Journal of Fluid Mechanics / Volume 485 / 25 May 2003
- Published online by Cambridge University Press:
- 24 June 2003, pp. 279-306
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We consider the problem of nonlinear steady convection in a horizontal mushy layer rotating about a vertical axis. We analyse the stationary modes of convection in the form of two-dimensional oblique rolls and three-dimensional distorted patterns. Under a near-eutectic approximation and the limit of large far-field temperature, we determine the two- and three-dimensional solutions to the weakly nonlinear problem by using a perturbation technique, and the stability of these solutions is investigated with respect to arbitrary three-dimensional disturbances. The results of the analyses in a particular range of values of the amplitude of convection indicate in particular that, over most of the range of values of the parameters, subcritical convection in the form of down-hexagons with down-flow at the cell centres and up-flow at the cell boundaries can be preferred over up-hexagonal convection, where the convective flow is upward at the cell centres and downward at the cell boundaries. For zero or very small values of ${\cal T}$ (${\cal T}\,{\ll}\,1$), which is the square root of a Taylor number, rolls are preferred over supercritical rectangles, while supercritical rectangles, which are characterized by an angle $\gamma$ of about $60^\circ$, are stable and preferred over the rolls for T above some value. Here, $\gamma$ or $180^\circ-\gamma$ are the angles between any two adjacent wavenumber vectors of a rectangular cell. For increasing values of T, these rectangles become subcritically unstable and are replaced by new supercritical rectangles of higher $\gamma$ values, and $\gamma$ increases with T until supercritical squares ($\gamma\,{=}\,90^\circ$) become stable. The significance and realizability of down-hexagons, rectangles and squares are found to be due to the interactions between the local solid fraction and the flow associated with the Coriolis term in the momentum–Darcy equation that are fully taken into account in the present study.
On nonlinear convection in mushy layers Part 1. Oscillatory modes of convection
- D. N. RIAHI
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- Journal:
- Journal of Fluid Mechanics / Volume 467 / 25 September 2002
- Published online by Cambridge University Press:
- 24 September 2002, pp. 331-359
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We consider the problem of nonlinear convection in horizontal mushy layers during the solidification of binary alloys. We analyse the oscillatory modes of convection in the form of two- and three-dimensional travelling and standing waves. Under a near-eutectic approximation and the limit of large far-field temperature, we determine the solutions to the nonlinear problem by using a perturbation technique, and the stability of two- and three-dimensional solutions in the form of simple travelling waves, general travelling waves and standing waves is investigated. The results of the stability and the nonlinear analyses indicate that supercritical simple travelling rolls are stable over most of the studied range of parameter values, while supercritical standing rolls can be stable only over some small range of parameter values, where the simple travelling rolls are unstable. The results of the investigation of the onset of plume convection and chimney formation leading to the occurrence of freckles in the alloy crystal indicate that the chimney of the plume can be generated internally or near the lower boundary of the mushy layer. The roles of a Stefan number, a permeability parameter and a concentration ratio on the flow instability in both linear and nonlinear regimes are also determined.