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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

Byline: Michel G. J. Elzen (1), Detlef P. Vuuren (1), Jasper Vliet (1) Abstract: Substantially postponing the emission reductions, compared to the ranges indicated in IPCC's recent assessment for 2020 as required for meeting the longterm 2degC target, increases the risk of exceeding this target. The costs of a delay strategy are lower in the short term, but leads to higher costs in the longer term. The analysis shows if the emission reductions are postponed to 2030 it is not likely that higher emissions from the earlier years can be fully compensated in future decades in a so-called 'delayed action scenario'. A full compensation would require emission reduction rates in the coming decades that are much higher than those found in the scenario literature. Without compensation, the risk of exceeding the global temperature rise target of 2degC will increase. This confirms that it is not only the reduction commitments for 2050 that determine the risk of exceeding the 2degC target, but also the path between now and 2050. To meet this 2degC target, more ambitious 2020 reduction targets are needed for the developed and developing countries than those that have been pledged so far. Author Affiliation: (1) Netherlands Environmental Assessment Agency, Bilthoven, The Netherlands Article History: Registration Date: 04/01/2010 Received Date: 13/10/2009 Accepted Date: 02/01/2010 Online Date: 14/01/2010 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s10584-010-9798-5) contains supplementary material, which is available to authorized users.

Byline: Elke Stehfest (1), Lex Bouwman (1,2), Detlef P. Vuuren (1), Michel G. J. Elzen (1), Bas Eickhout (1), Pavel Kabat (2) Abstract: Climate change mitigation policies tend to focus on the energy sector, while the livestock sector receives surprisingly little attention, despite the fact that it accounts for 18% of the greenhouse gas emissions and for 80% of total anthropogenic land use. From a dietary perspective, new insights in the adverse health effects of beef and pork have lead to a revision of meat consumption recommendations. Here, we explored the potential impact of dietary changes on achieving ambitious climate stabilization levels. By using an integrated assessment model, we found a global food transition to less meat, or even a complete switch to plant-based protein food to have a dramatic effect on land use. Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned, resulting in a large carbon uptake from regrowing vegetation. Additionally, methane and nitrous oxide emission would be reduced substantially. A global transition to a low meat-diet as recommended for health reasons would reduce the mitigation costs to achieve a 450 ppm CO.sub.2-eq. stabilisation target by about 50% in 2050 compared to the reference case. Dietary changes could therefore not only create substantial benefits for human health and global land use, but can also play an important role in future climate change mitigation policies. Author Affiliation: (1) Netherlands Environmental Assessment Agency, Global Sustainability and Climate, P.O. Box 303, 3720 AH, Bilthoven, The Netherlands (2) Earth System Science and Climate Change Group, Wageningen University Research Centre (WUR), P.O. Box 47, 6700 AA, Wageningen, The Netherlands Article History: Registration Date: 26/11/2008 Received Date: 11/04/2008 Accepted Date: 24/10/2008 Online Date: 04/02/2009

Byline: Michel G. J. Elzen (1), Paul L. Lucas (1), Detlef P. van Vuuren (1) Abstract: This paper assesses regional abatement action and costs for two scenarios in which atmospheric greenhouse gas concentrations stabilise at 450 and 550 ppm CO.sub.2-equivalent. It evaluates two allocation schemes: Multi-Stage and Contraction & Convergence. It was found that abatement costs as percentages of GDP vary significantly by region, with high costs for the Middle East and the former Soviet Union, medium costs for the OECD regions and low costs or even gains for (other) developing regions. In addition to the abatement costs they incur, fossil-fuel-exporting regions are also likely to be affected by losses of coal and oil exports while the former Soviet Union and South America could experience increased bio-energy exports. Especially in the former Soviet Union and Asia, non-CO.sub.2 abatement options are important in the short term in reducing their emissions. Carbon capture and storage, energy efficiency improvements, bio-energy use and the use of renewables dominate reductions in the long term in all regions. It was found that the regional costs are influenced more by the assumed stabilisation level and baseline scenario than by the allocation regimes explored or the assumptions for different technologies. Author Affiliation: (1) Netherlands Environmental Assessment Agency (MNP), P.O. Box 303, 3720 AH, Bilthoven, The Netherlands Article History: Registration Date: 17/06/2008 Received Date: 20/01/2006 Accepted Date: 04/04/2008 Online Date: 03/09/2008

Byline: Detlef P. Vuuren (1), Michel G. J. Elzen (1), Paul L. Lucas (1), Bas Eickhout (1), Bart J. Strengers (1), Bas Ruijven (1), Steven Wonink (1), Roy Houdt (1) Abstract: On the basis of the IPCC B2, A1b and B1 baseline scenarios, mitigation scenarios were developed that stabilize greenhouse gas concentrations at 650, 550 and 450 and -- subject to specific assumptions -- 400 ppm CO.sub.2-eq. The analysis takes into account a large number of reduction options, such as reductions of non-CO.sub.2 gases, carbon plantations and measures in the energy system. The study shows stabilization as low as 450 ppm CO.sub.2-eq. to be technically feasible, even given relatively high baseline scenarios. To achieve these lower concentration levels, global emissions need to peak within the first two decades. The net present value of abatement costs for the B2 baseline scenario (a medium scenario) increases from 0.2% of cumulative GDP to 1.1% as the shift is made from 650 to 450 ppm. On the other hand, the probability of meeting a two-degree target increases from 0%--10% to 20%--70%. The mitigation scenarios lead to lower emissions of regional air pollutants but also to increased land use. The uncertainty in the cost estimates is at least in the order of 50%, with the most important uncertainties including land-use emissions, the potential for bio-energy and the contribution of energy efficiency. Furthermore, creating the right socio-economic and political conditions for mitigation is more important than any of the technical constraints. Author Affiliation: (1) Netherlands Environmental Assessment Agency (MNP), P.O. Box 303, 3720 AH, Bilthoven, The Netherlands Article History: Registration Date: 28/06/2006 Received Date: 12/12/2005 Accepted Date: 09/05/2006 Online Date: 13/02/2007

The bottom-up approach of the Nationally Determined Contributions (NDCs) in the Paris Agreement has led countries to self-determine their greenhouse gas (GHG) emission reduction targets. The planned 'ratcheting-up' process, which aims to ensure that the NDCs comply with the overall goal of limiting global average temperature increase to well below 2 °C or even 1.5 °C, will most likely include some evaluation of 'fairness' of these reduction targets. In the literature, fairness has been discussed around equity principles, for which many different effort-sharing approaches have been proposed. In this research, we analysed how country-level emission targets and carbon budgets can be derived based on such criteria. We apply novel methods directly based on the global carbon budget, and, for comparison, more commonly used methods using GHG mitigation pathways. For both, we studied the following approaches: equal cumulative per capita emissions, contraction and convergence, grandfathering, greenhouse development rights and ability to pay. As the results critically depend on parameter settings, we used the wide authorship from a range of countries included in this paper to determine default settings and sensitivity analyses. Results show that effort-sharing approaches that (i) calculate required reduction targets in carbon budgets (relative to baseline budgets) and/or (ii) take into account historical emissions when determining carbon budgets can lead to (large) negative remaining carbon budgets for developed countries. This is the case for the equal cumulative per capita approach and especially the greenhouse development rights approach. Furthermore, for developed countries, all effort-sharing approaches except grandfathering lead to more stringent budgets than cost-optimal budgets, indicating that cost-optimal approaches do not lead to outcomes that can be regarded as fair according to most effort-sharing approaches. [ABSTRACT FROM AUTHOR]

The United Nations Framework Convention on Climate Change (UNFCCC ) 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 CO2 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 CO2). [ABSTRACT FROM AUTHOR]

This paper assesses regional abatement action and costs for two scenarios in which atmospheric greenhouse gas concentrations stabilise at 450 and 550 ppm CO2-equivalent. It evaluates two allocation schemes: Multi-Stage and Contraction & Convergence. It was found that abatement costs as percentages of GDP vary significantly by region, with high costs for the Middle East and the former Soviet Union, medium costs for the OECD regions and low costs or even gains for (other) developing regions. In addition to the abatement costs they incur, fossil-fuel-exporting regions are also likely to be affected by losses of coal and oil exports while the former Soviet Union and South America could experience increased bio-energy exports. Especially in the former Soviet Union and Asia, non-CO2 abatement options are important in the short term in reducing their emissions. Carbon capture and storage, energy efficiency improvements, bio-energy use and the use of renewables dominate reductions in the long term in all regions. It was found that the regional costs are influenced more by the assumed stabilisation level and baseline scenario than by the allocation regimes explored or the assumptions for different technologies. [ABSTRACT FROM AUTHOR]

Abstract During the negotiations on the Kyoto Protocol, Brazil proposed allocating the greenhouse gas emission reductions of Annex I Parties according to the relative effect of a country’s historical emissions on global temperature increase. This paper analyses the impact of scientific uncertainties and of different options in policy implementation (policy choices) on the contribution of countries’ historical emissions to indicators of historical responsibility for climate change. The influence of policy choices was found to be at least as large as the impact of the scientific uncertainties analysed here. Building on this, the paper then proceeds to explore the implications of applying the Brazilian Proposal as a climate regime for differentiation of future commitments on the global scale combined with an income threshold for participation of the non-Annex I regions. Under stringent climate targets, such a regime leads to high emission reductions for Annex I regions by 2050, in particular for Europe and Japan. The income threshold assumptions strongly affect the Annex I reductions, even more than the impact of another burden-sharing key. A variant of the Brazilian Proposal, allocating emission reductions on the basis of cumulative emissions since 1990, would lead to a more balanced distribution of emission reductions. [ABSTRACT FROM AUTHOR]