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To understand how global warming can be kept well below 2 degrees Celsius and even 1.5 degrees Celsius, climate policy uses scenarios that describe how society could reduce its greenhouse gas emissions. However, current scenarios have a key weakness: they typically focus on reaching specific climate goals in 2100. This choice may encourage risky pathways that delay action, reach higher-than-acceptable mid-century warming, and rely on net removal of carbon dioxide thereafter to undo their initial shortfall in reductions of emissions. Here we draw on insights from physical science to propose a scenario framework that focuses on capping global warming at a specific maximum level with either temperature stabilization or reversal thereafter. The ambition of climate action until carbon neutrality determines peak warming, and can be followed by a variety of long-term states with different sustainability implications. The approach proposed here closely mirrors the intentions of the United Nations Paris Agreement, and makes questions of intergenerational equity into explicit design choices. Fundamental value judgments about acceptable maximum levels of climate change and future reliance on controversial technologies can be made explicitly in climate scenarios, thereby addressing the intergenerational bias present in the scenario literature., Author(s): Joeri Rogelj [sup.1] [sup.2] [sup.3] , Daniel Huppmann [sup.1] , Volker Krey [sup.1] [sup.4] , Keywan Riahi [sup.1] [sup.5] , Leon Clarke [sup.6] , Matthew Gidden [sup.1] , Zebedee [...]

Author(s): Jessica Jewell (corresponding author) [1, 2]; David McCollum [1, 3]; Johannes Emmerling [4, 5]; Christoph Bertram [6]; David E. H. J. Gernaat [7, 8]; Volker Krey [1]; Leonidas Paroussos [...]

The Paris climate agreement aims at holding global warming to well below 2 degrees Celsius and to 'pursue efforts' to limit it to 1.5 degrees Celsius. To accomplish this, countries have submitted Intended Nationally Determined Contributions (INDCs) outlining their post-2020 climate action. Here we assess the effect of current INDCs on reducing aggregate greenhouse gas emissions, its implications for achieving the temperature objective of the Paris climate agreement, and potential options for overachievement. The INDCs collectively lower greenhouse gas emissions compared to where current policies stand, but still imply a median warming of 2.6-3.1 degrees Celsius by 2100. More can be achieved, because the agreement stipulates that targets for reducing greenhouse gas emissions are strengthened over time, both in ambition and scope. Substantial enhancement or over-delivery on current INDCs by additional national, sub-national and non-state actions is required to maintain a reasonable chance of meeting the target of keeping warming well below 2 degrees Celsius., In December 2015, the Paris Agreement (1)--a new global agreement to combat climate change--was adopted under the United Nations Framework Convention on Climate Change (UNFCCC). In preparation of this agreement, [...]

The most important energy development of the past decade has been the wide deployment of hydraulic fracturing technologies that enable the production of previously uneconomic shale gas resources in North America (1). If these advanced gas production technologies were to be deployed globally, the energy market could see a large influx of economically competitive unconventional gas resources (2). The climate implications of such abundant natural gas have been hotly debated. Some researchers have observed that abundant natural gas substituting for coal could reduce carbon dioxide (C[O.sub.2]) emissions (3-6). Others have reported that the non-C[O.sub.2] greenhouse gas emissions associated with shale gas production make its lifecycle emissions higher than those of coal (7, 8). Assessment of the full impact of abundant gas on climate change requires an integrated approach to the global energy-economy- climate systems, but the literature has been limited in either its geographic scope (9, 10) or its coverage of greenhouse gases (2). Here we show that market-driven increases in global supplies of unconventional natural gas do not discernibly reduce the trajectory of greenhouse gas emissions or climate forcing. Our results, based on simulations from five state-of-the-art integrated assessment models (11) of energy-economy- climate systems independently forced by an abundant gas scenario, project large additional natural gas consumption of up to + 170 per cent by 2050. The impact on C[O.sub.2] emissions, however, is found to be much smaller (from -2 per cent to +11 per cent), and a majority of the models reported a small increase in climate forcing (from -0.3 per cent to +7 per cent) associated with the increased use of abundant gas. Our results show that although market penetration of globally abundant gas may substantially change the future energy system, it is not necessarily an effective substitute for climate change mitigation policy (9, 10)., Five research teams projected the evolution of the future global energy system up to 2050 under two alternative assumptions about natural gas supply: 'Conventional Gas' and 'Abundant Gas' (Fig. 1 [...]

For more than a decade, the target of keeping global warming below 2 ° C has been a key focus of the international climate debate. (1) In response, the scientific [...]

Byline: Detlef P. Vuuren (1), Jae Edmonds (2), Steven J. Smith (2), Kate V. Calvin (2), Joseph Karas (2), Mikiko Kainuma (3), Nebojsa Nakicenovic (4,5), Keywan Riahi (4), Bas J. Ruijven (1), Rob Swart (6), Allison Thomson (2) Abstract: Long-term scenarios developed by integrated assessment models are used in climate research to provide an indication of plausible long-term emissions of greenhouse gases and other radiatively active substances based on developments in the global energy system, land-use and the emissions associated with these systems. The phenomena that determine these long-term developments (several decades or even centuries) are very different than those that operate on a shorter time-scales (a few years). Nevertheless, in the literature, we still often find direct comparisons between short-term observations and long-term developments that do not take into account the differing dynamics over these time scales. In this letter, we discuss some of the differences between the factors that operate in the short term and those that operate in the long term. We use long-term historical emissions trends to show that short-term observations are very poor indicators of long-term future emissions developments. Based on this, we conclude that the performance of long-term scenarios should be evaluated against the appropriate, corresponding long-term variables and trends. The research community may facilitate this by developing appropriate data sets and protocols that can be used to test the performance of long-term scenarios and the models that produce them. Author Affiliation: (1) Netherlands Environmental Assessment Agency, Postbus, 303 3720, AH, Bilthoven, The Netherlands (2) Pacific Northwest National Laboratory, Joint Global Change Research Institute, College Park, MD, 20740, USA (3) National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba, Ibaraki, 305-8506, Japan (4) International Institute for Applied System Analysis, Schlossplatz 1, 2361, Laxenburg, Austria (5) Vienna University of Technology, Gusshausstrasse 25-29/37320, 1040, Vienna, Austria (6) Wageningen University and Research Centre, Earth System Science and Climate Change Group, Droevendaalsesteeg 4, 6708 PB, Wageningen, The Netherlands Article History: Registration Date: 05/10/2010 Received Date: 29/07/2010 Accepted Date: 01/10/2010 Online Date: 26/10/2010 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s10584-010-9940-4) contains supplementary material, which is available to authorized users.

Byline: Christian Azar (1), Kristian Lindgren (1), Michael Obersteiner (2), Keywan Riahi (2), Detlef P. Vuuren (3), K. Michel G. J. Elzen (3), Kenneth Mollersten (2), Eric D. Larson (4,5) Abstract: The United Nations Framework Convention on Climate Change (UNFCCC 1992) calls for stabilization of atmospheric greenhouse gas (GHG) concentrations at a level that would prevent dangerous anthropogenic interference with the climate system. We use three global energy system models to investigate the technological and economic attainability of meeting CO.sub.2 concentration targets below current levels. Our scenario studies reveal that while energy portfolios from a broad range of energy technologies are needed to attain low concentrations, negative emission technologies--e.g., biomass energy with carbon capture and storage (BECCS)--significantly enhances the possibility to meet low concentration targets (at around 350 ppm CO.sub.2). Author Affiliation: (1) Department of Physical Resource Theory, Chalmers University of Technology, 412 96, Goteborg, Sweden (2) International Institute for Applied Systems Analysis (IIASA), 2361, Laxenburg, Austria (3) Netherlands Environmental Assessment Agency, PO Box 303, 3729, AH Bilthoven, The Netherlands (4) Princeton Environmental Institute, Princeton University, Guyot Hall, Washington Road, Princeton, NJ, 08544, USA (5) Climate Central, Inc., 1 Palmer Square, Princeton, NJ, 08542, USA Article History: Registration Date: 10/03/2010 Received Date: 28/12/2009 Accepted Date: 09/03/2010 Online Date: 20/05/2010

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth's climate system and its likely response to human and natural influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community., To improve understanding of the complex interactions of the climate system, ecosystems, and human activities and conditions' the research community develops and uses scenarios. These scenarios provide plausible descriptions of [...]

Midcentury targets have been proposed as a guide to climate change policy that can link long-term goals to shorter-term actions. However no explicit mitigation analyses have been carried out of the relationship between midcentury conditions and longer-term outcomes. Here we use an integrated assessment modeling framework with a detailed representation of the energy sector to examine the dependence of climate change outcomes in 2100 on emissions levels, atmospheric concentrations, and technology characteristics in 2050. We find that midcentury conditions are crucial determinants of longer-term climate outcomes, and we identify feasibility thresholds describing conditions that must be met by midcentury to keep particular long-term options open. For example, to preserve the technical feasibility of a 50% likelihood of keeping global average temperature at climate change | integrated assessment | emission target | mitigation doi/10.1073/pnas.0903797106

Byline: Detlef P. Vuuren (1), Keywan Riahi (2) Author Affiliation: (1) Netherlands Environment Assessment Agency, P.O. Box 303, 3720 AH, Bilthoven, The Netherlands (2) IIASA, Schlossplatz 1, A-2361, Laxenburg, Austria Article History: Registration Date: 22/07/2008 Received Date: 20/06/2008 Accepted Date: 18/07/2008 Online Date: 10/09/2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.techfore.2006.05.026 Byline: Keywan Riahi (a), Arnulf Grubler (a)(b), Nebojsa Nakicenovic (a)(c) Abstract: This paper presents an overview of the greenhouse gas (GHG) emissions scenarios that form the analytical backbone for other contributions to this Special Issue. We first describe the motivation behind this scenario exercise and introduce the main scenario features and characteristics, in both qualitative and quantitative terms. Altogether, we analyze three 'baseline' scenarios of different socio-economic and technological developments that are assumed not to include any explicit climate policies. We then impose a range of climate stabilization targets on these baseline scenarios and analyze in detail the feasibility, costs and uncertainties of meeting a range of different climate stabilization targets in accordance with Article 2 of the United Nations Framework Convention on Climate Change. The scenarios were developed by the IIASA Integrated Assessment Modeling Framework that encompasses detailed representations of the principal GHG-emitting sectors -- energy, industry, agriculture, and forestry. The main analytical findings from our analysis focus on the implications of salient uncertainties (associated with scenario baselines and stabilization targets), on feasibility and costs of climate stabilization efforts, and on the choice of appropriate portfolios of emissions abatement measures. We further analyze individual technological options with regards to their aggregated cumulative contribution toward emissions mitigation during the 21st century as well as their deployment over time. Our results illustrate that the energy sector will remain by far the largest source of GHG emissions and hence remain the prime target of emissions reduction. Ultimately, this may lead to a complete restructuring of the global energy system. Climate mitigation could also significantly change the relative economics of traditional versus new, more climate friendly products and services. This is especially the case within the energy system, which accounts for the largest share of emissions reductions, but it is also the case in the agriculture and forestry sectors, where emissions reduction and sink enhancement measures are relatively more modest. Author Affiliation: (a) Transitions to New Technologies Program, International Institute for Applied Systems Analysis, Laxenburg, Austria (b) School of Forestry and Environmental Studies, Yale University, New Haven, CT, USA (c) Department of Power Systems and Energy Economics, Technical University Vienna, Austria Article History: Received 4 March 2006; Revised 10 March 2006; Accepted 24 May 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.techfore.2006.05.024 Byline: Ilkka Keppo (a), Brian C. O'Neill (a)(b), Keywan Riahi (a) Keywords: Climate change; Energy modeling; Climate sensitivity; Uncertainty analysis Abstract: This paper explores the implications for global average temperature change of a set of reference and mitigation scenarios in a probabilistic framework. First, we use published probability density functions for climate sensitivity to investigate the likelihood of achieving targets expressed as levels or rates of global average temperature change. We find, for example, that limiting warming to 3 C above pre-industrial levels with at least a medium likelihood requires cumulative emissions reductions on the order of 30-60% below one unmitigated reference scenario by 2100, while a more favorable baseline scenario requires no reductions at all to achieve this outcome with the same likelihood. We further conclude that the rate of temperature change may prove to be more difficult to control, especially if most of the mitigation effort is postponed until later in the century. Rate of change targets of 0.1-0.2 [degrees]C/decade are unlikely to be achieved by a target for the long-term level of climate change alone. Second, we quantify relationships between mitigation costs and the likelihood of achieving various targets and show how this depends strongly on the reference scenario. Third, we explore relationships between medium-term achievements and long-term climate change outcomes. Our results suggest that atmospheric concentrations and the share of zero-carbon energy in the middle of the 21st century are key indicators of the likelihood of meeting long-term climate change goals cost-effectively. They also suggest that interim targets could be an effective means of keeping long-term target options open. Our analysis shows that least-cost mitigation strategies for reaching low climate change targets include a wide portfolio of reduction measures. In particular, fundamental long-term structural changes in the energy system in these scenarios are a necessary but not sufficient condition to achieve high likelihoods for low temperature targets. The cost-effective portfolio of emissions reductions must also address demand-side measures and include mitigation options in the industry, agriculture, and the forest sector. Author Affiliation: (a) International Institute for Applied Systems Analysis, Laxenburg, Austria (b) Watson Institute for International Studies, Brown University, Providence, RI, USA Article History: Received 7 February 2006; Revised 14 May 2006; Accepted 24 May 2006

The usefulness of combined energy systems and a macroeconomic model, for the examination of a global impacts of an energy policy that internalizes the external costs of electricity generation, is discussed.

The non-C[O.sub.2] greenhouse gases have so far jointly contributed around 40 percent to overall global warming. In this paper we examine the role of non-C[O.sub.2] greenhouse gases in meeting long-term [...]

This paper examines the role of technological change and spillovers within the context of a climate policy in a long-term scenario of the global energy system. We use the energy-systems [...]

This paper examines the role of technological change and spillovers within the context of a climate policy in a long-term scenario of the global energy system. We use the energy-systems [...]

BACKGROUND: Approximately 2.8 billion people cook with solid fuels. Research has focused on the health impacts of indoor exposure to fine particulate pollution. Here, for the 2010 Global Burden of Disease project (GBD 2010), we evaluated the impact of household cooking with solid fuels on regional population-weighted ambient [PM.sub.2.5] (particulate matter [less than or equal to] 2.5 [micro]m) pollution ([APM.sub.2.5]). OBJECTIVES: We estimated the proportion and concentrations of [APM.sub.2.5] attributable to household cooking with solid fuels ([PM.sub.2.5-cook]) for the years 1990, 2005, and 2010 in 170 countries, and associated ill health. METHODS: We used an energy supply--driven emissions model (GAINS; Greenhouse Gas and Air Pollution Interactions and Synergies) and source-receptor model (TM5-FASST) to estimate the proportion of [APM.sub.2.5] produced by households and the proportion of household [PM.sub.2.5] emissions from cooking with solid fuels. We estimated health effects using GBD 2010 data on ill health from [APM.sub.2.5] exposure. RESULTS: In 2010, household cooking with solid fuels accounted for 12% of [APM.sub.2.5] globally, varying from 0% of [APM.sub.2.5] in five higher-income regions to 37% (2.8 [micro]g/[m.sup.3] of 6.9 [micro]g/[m.sup.3] total) in southern sub-Saharan Africa. [PM.sub.2.5-cook] constituted > 10% of [APM.sub.2.5] in seven regions housing 4.4 billion people. South Asia showed the highest regional concentration of [APM.sub.2.5] from household cooking (8.6 [micro]g/[m.sup.3]). On the basis of GBD 2010, we estimate that exposure to [APM.sub.2.5] from cooking with solid fuels caused the loss of 370,000 lives and 9.9 million disability-adjusted life years globally in 2010. CONCLUSIONS: [PM.sub.2.5] emissions from household cooking constitute an important portion of [APM.sub.2.5] concentrations in many places, including India and China. Efforts to improve ambient air quality will be hindered if household cooking conditions are not addressed. Citation: Chafe ZA, Brauer M, Klimont Z, Van Dingenen R, Mehta S, Rao S, Riahi K, Dentener F, Smith KR. 2014. Household cooking with solid fuels contributes to ambient PM2.5 air pollution and the burden of disease. Environ Health Perspect 122:1314-1320; http://dx.doi.org/10.1289/ehp.1206340, Introduction Approximately 2.8 billion people, more than ever before in human history, use solid fuels, including wood, coal, charcoal, and agricultural residues, for cooking (Bonjour et al. 2013). Solid fuel [...]

Byline: Hans-Holger Rogner, Alan McDonald, Keywan Riahi This paper estimates investment cost targets for future nuclear power plants to be competitive in mid-21st century energy markets and beyond. The point of departure is the nuclear market shares derived from the Special Report on Emissions Scenarios (SRES) of the Intergovernmental Panel on Climate Change. One provocative result is that substantial nuclear expansion does not seem to require big reductions in nuclear investment costs, largely explained by the difference between cost reductions consistent with long-term energy system optimisation based on perfect foresight, and cost reductions necessary to attract private investment in today's deregulating and uncertain energy markets.

Byline: Hans-Holger Rogner, Alan McDonald, Keywan Riahi This paper outlines a range of scenarios describing what the world's energy system might look like in the middle of the century, and what nuclear energy's role might be. The starting point is the 40 non-greenhouse-gas-mitigation scenarios in the Special Report on Emissions Scenarios (SRES) of the Intergovernmental Panel on Climate Change (IPCC). Four illustrative marker scenarios are selected and include growing but varying contributions from nuclear power to electricity supply, while in some scenarios nuclear energy also supplements hydrogen supply by 2050. For each marker scenario, the paper analyses the generic design features of future nuclear power technologies and fuel cycles consistent with the underlying scenario storylines.

Byline: Ger Klaassen, Keywan Riahi, R. Alexander Roehrl This paper examines the implications of the new dynamics-as-usual IPCC B2 scenario for the viability of international gas transmission lines and the environment in Eurasia. In doing so, it analyses the effects of increasing the number of pipelines, reducing gas extraction costs and stabilising greenhouse gas concentrations. In the B2 scenario, interregional gas transport by pipeline would increase from 150 bcm (billion cubic metres) in 1998 to nearly 900 bcm in 2040 whereas the interregional liquefied natural gas (LNG) trade would decrease over the same period. In addition, connecting the natural gas supply areas in the Former Soviet Union and the Middle East with the demand centres in South and Central Asia would increase global piped gas exports to around 1780 bcm. Reducing extraction costs or stabilising greenhouse gas concentrations would not alter this picture drastically. Although less than under a coal based scenario, carbon emissions would still increase under the B2 scenario, especially when gas extraction costs decrease. Sulphur emissions in Asia would, however, be significantly lower than in a coal-based scenario.