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More than 100 countries have communicated or adopted new Nationally Determined Contributions (NDCs) and net-zero target pledges. We investigate the impact on global, national, sectoral, and individual greenhouse gas emissions projections under different scenarios based on the announced NDCs and net-zero pledges using the IMAGE integrated assessment model. Our results show that while the net-zero pledges, if implemented, could be an important step forward, they are still not enough to achieve the Paris Agreement goals of well below 2°C and preferably 1.5°C by the end of the century. Still, our net-zero scenarios project significant all-sector decarbonization, in particular, electricity; however, certain sectors like industry and transport prove hard to completely abate., (© 2023 New York Academy of Sciences.)

Modern sustainable bioenergy can contribute toward mid‐century European energy decarbonization targets by replacing fossil fuels. Fulfilling this role would require access to increased volumes of bioenergy, with extra‐EU imports projected to play an important part. Access to this resource on the international marketplace is not governed by Europe's economic competitiveness alone. This study investigates geopolitical, socioeconomic, and regulatory considerations that can influence Europe's bioenergy imports but that are so far underexplored. The effect of these constraints on European import volumes, sourcing regions, mitigation potential, and their implications for European and global emissions is projected to the year 2050 using a global integrated assessment model. The projections show that Europe can significantly increase imports from 1.5 EJ year−1 in 2020 to 8.1 EJ year−1 by 2050 whilst remaining compliant with Renewables Energy Directive recast II (RED II) greenhouse gas (GHG) criteria. Under these conditions, bioenergy could provide annual GHG mitigation of 0.44 GtCO2eq. in 2050. However, achieving this would require a structural diversification of trading partners from the present. Furthermore, socioeconomic and logistical concerns may limit the feasibility of some of the projected major sourcing regions, including Africa and South America. Failure to overcome these challenges within supplying regions could limit European imports by 60%, reducing annual mitigation to 0.16 GtCO2eq. in 2050. From a global perspective, regions with a comparatively carbon‐intense energy system offer an alternative destination for globally traded biomass that could increase the mitigative potential of bioenergy. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Over 100 countries have set or are considering net-zero emissions or neutrality targets. However, most of the information on emissions neutrality (such as timing) is provided for the global level. Here, we look at national-level neutrality-years based on globally cost-effective 1.5 °C and 2 °C scenarios from integrated assessment models. These results indicate that domestic net zero greenhouse gas and CO2 emissions in Brazil and the USA are reached a decade earlier than the global average, and in India and Indonesia later than global average. These results depend on choices like the accounting of land-use emissions. The results also show that carbon storage and afforestation capacity, income, share of non-CO2 emissions, and transport sector emissions affect the variance in projected phase-out years across countries. We further compare these results to an alternative approach, using equity-based rules to establish target years. These results can inform policymakers on net-zero targets. Over 100 countries have set or are considering net-zero emissions targets. Here, the authors show that a country's potential for negative emissions and methodological issues affect when countries can reach net-zero, calling for clear internationally agreed definitions and accounting methods. [ABSTRACT FROM AUTHOR]

Several studies have shown that the greenhouse gas reduction resulting from the current nationally determined contributions (NDCs) will not be enough to meet the overall targets of the Paris Climate Agreement. It has been suggested that more ambition mitigations of short-lived climate forcer (SLCF) emissions could potentially be a way to reduce the risk of overshooting the 1.5 or 2 °C target in a cost-effective way. In this study, we employ eight state-of-the-art integrated assessment models (IAMs) to examine the global temperature effects of ambitious reductions of methane, black and organic carbon, and hydrofluorocarbon emissions. The SLCFs measures considered are found to add significantly to the effect of the NDCs on short-term global mean temperature (GMT) (in the year 2040: − 0.03 to − 0.15 °C) and on reducing the short-term rate-of-change (by − 2 to 15%), but only a small effect on reducing the maximum temperature change before 2100. This, because later in the century under assumed ambitious climate policy, SLCF mitigation is maximized, either directly or indirectly due to changes in the energy system. All three SLCF groups can contribute to achieving GMT changes. [ABSTRACT FROM AUTHOR]

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]

• Long-term non-CO 2 MAC curves developed based on most recent literature. • Includes all major non-CO 2 emission sources and mitigation measures for 26 world regions. • Maximum reduction potential of nitrous oxide estimated higher, of methane lower. • Overall non-CO 2 mitigation estimated at 58% in 2050 and 71% in 2100. • Delayed climate action can lower mitigation potentials. This study presents a new comprehensive set of long-term Marginal Abatement Cost (MAC) curves of all major non-CO 2 greenhouse gas emission sources. The work builds on existing short-term MAC curve datasets and recent literature on individual mitigation measures. The new MAC curves include current technology and costs information as well as estimates of technology development and removal of implementation barriers to capture long-term dynamics. Compared to earlier work, we find a higher projected maximum reduction potential (MRP) of nitrous oxide (N 2 O) and a lower MRP of methane (CH 4). The combined MRP for all non-CO 2 gases is similar but has been extended to also capture mitigation measures that can be realized at higher implementation costs. When applying the new MAC curves in a cost-optimal, integrated assessment model-based 2.6 W/m2 scenario, the total non-CO 2 mitigation is projected to be 10.9 Mt CO 2 equivalents in 2050 (i.e. 58% reduction compared to baseline emissions) and 15.6 Mt CO 2 equivalents in 2100 (i.e. a 71% reduction). In applying the new MAC curves, we account for inertia in thline implementation speed of mitigation measures. Although this does not strongly impact results in an optimal strategy, it means that the contribution of non-CO 2 mitigation could be more limited if ambitious climate policy is delayed. [ABSTRACT FROM AUTHOR]

This paper uses decomposition analysis to investigate the key contributions to changes in greenhouse gas emissions in different scenarios. We derive decomposition formulas for the three highest-emitting sectors: power generation, industry, and transportation (both passenger and freight). These formulas were applied to recently developed 1.5 °C emission scenarios by the Integrated Model to Assess the Global Environment (IMAGE), emphasising the role of renewables and lifestyle changes. The decomposition analysis shows that carbon capture and storage (CCS), both from fossil fuel and bioenergy burning, renewables and reducing carbon intensity provide the largest contributions to emission reduction in the scenarios. Efficiency improvement is also critical, but part of the potential is already achieved in the Baseline scenario. The relative importance of different emission reduction drivers is similar in the OECD (characterised by relatively high per capita income levels and emissions) and non-OECD (characterised by relatively high carbon intensities of the economy) region, but there are some noteworthy differences. In the non-OECD region, improving efficiency in industry and transport and increasing the share of renewables in power generation are more important in reducing emissions than in the OECD region, while CCS in power generation and electrification of passenger transport are more important drivers in the OECD region. [ABSTRACT FROM AUTHOR]

The Bali Action Plan as adopted under the United Nations Framework Convention on Climate Change (UNFCCC) in 2007, states that Annex I (developed) countries should reduce their greenhouse gas emissions, based on comparable efforts. Within this context, we have explored various comparable effort approaches (for example, equal marginal abatement costs for all countries) for reducing emissions by the year 2020 for individual countries and regions. In all calculations, the total reduction for Annex I countries as a group is assumed to be 30% below 1990 levels. In the analysis, we compare the reduction targets as calculated from the different approaches with the emission reductions as pledged by these countries as part of the Copenhagen Accord, as drafted under the UNFCCC in 2009. Our analysis indicates that the different elements in these calculations may cause a diversity in outcomes and that, therefore, individual countries may favour certain elements over others. These elements include (a) the choice of the approach itself (the same approach may produce very different outcomes for countries with diverging national circumstances, such as Canada and Russia); (b) the reference year (such as 1990 or 2006 emissions, is very important for countries with an increase in emissions since 1990 (e.g. the United States, Canada) or for those that have lower emission levels (e.g. Russia, the Ukraine)); and (c) rules on land use (these are important for countries with large forest areas). It should be noted that the stringency of the individual countries’ reductions as pledged, differs substantially from the stringency of the reduction targets calculated from the effort-sharing approaches. The current pledges by both the European Union and the United States, are lower than the reductions that would be obtained in the effort-sharing approaches for a 30% overall reduction in Annex I countries. [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]

Model analysis within the ADAM project has shown that achieving low greenhouse gas concentration levels, e.g. at 400ppm CO2-e is technologically feasible at costs of a few percent of GDP. However, models simplify the dynamics involved in implementing climate policy and the results depend on critical model assumptions such as global participation in climate policy and full availability of current and newly evolving technologies. The design of a low stabilization policy regime in the real world depends on factors that can only be partly covered by models. In this context, the paper reflects on limits of the integrated assessment models used to explore climate policy and addresses the issues of (i) how global participation might be achieved, (ii) which kind of options are available to induce deep GHG reductions inside and outside the energy sector, and (iii) which risks and which co-benefits of mitigation options are not assessed by the models. [ABSTRACT FROM AUTHOR]

This study gives a synthesis of a model comparison assessing the technological feasibility and economic consequences of achieving greenhouse gas concentration targets that are sufficiently low to keep the increase in global mean temperature below 2 degrees Celsius above pre-industrial levels. All five global energy-environment-economy models show that achieving low greenhouse gas concentration targets is technically feasible and economically viable. The ranking of the importance of individual technology options is robust across models. For the lowest stabilization target (400 ppm CO2 eq), the use of bio-energy in combination with CCS plays a crucial role, and biomass potential dominates the cost of reaching this target. Without CCS or the considerable extension of renewables the 400 ppm CO2 eq target is not achievable. Across the models, estimated aggregate costs up to 2100 are below 0.8% global GDP for 550 ppm CO2 eq stabilization and below 2.5%for the 400 ppm CO2 eq pathway. [ABSTRACT FROM AUTHOR]

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 CO2-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. [ABSTRACT FROM AUTHOR]

In this study, we analyze the impact of fertilizer- and manure-induced N2O emissions due to energy crop production on the reduction of greenhouse gas (GHG) emissions when conventional transportation fuels are replaced by first-generation biofuels (also taking account of other GHG emissions during the entire life cycle). We calculate the nitrous oxide (N2O) emissions by applying a statistical model that uses spatial data on climate and soil. For the land use that is assumed to be replaced by energy crop production (the ‘reference land-use system’), we explore a variety of options, the most important of which are cropland for food production, grassland, and natural vegetation. Calculations are also done in the case that emissions due to energy crop production are fully additional and thus no reference is considered. The results are combined with data on other emissions due to biofuels production that are derived from existing studies, resulting in total GHG emission reduction potentials for major biofuels compared with conventional fuels. The results show that N2O emissions can have an important impact on the overall GHG balance of biofuels, though there are large uncertainties. The most important ones are those in the statistical model and the GHG emissions not related to land use. Ethanol produced from sugar cane and sugar beet are relatively robust GHG savers: these biofuels change the GHG emissions by −103% to −60% (sugar cane) and −58% to −17% (sugar beet), compared with conventional transportation fuels and depending on the reference land-use system that is considered. The use of diesel from palm fruit also results in a relatively constant and substantial change of the GHG emissions by −75% to −39%. For corn and wheat ethanol, the figures are −38% to 11% and −107% to 53%, respectively. Rapeseed diesel changes the GHG emissions by −81% to 72% and soybean diesel by −111% to 44%. Optimized crop management, which involves the use of state-of-the-art agricultural technologies combined with an optimized fertilization regime and the use of nitrification inhibitors, can reduce N2O emissions substantially and change the GHG emissions by up to −135 percent points (pp) compared with conventional management. However, the uncertainties in the statistical N2O emission model and in the data on non-land-use GHG emissions due to biofuels production are large; they can change the GHG emission reduction by between −152 and 87 pp. [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: The conditional probabilistic scenario analysis combines statistical methods of uncertainty analysis at parameter level with storylines which recognize the deep uncertainty that exists for several underlying trends. The model calculations indicate that cumulative 21st century emissions could range from 800 to 2500GtC in the absence of climate policy. This range originates partly from the underlying storylines, and partly from the probabilistic analysis. Among the most important parameters contributing to the uncertainty range are uncertainty in income growth, population growth, parameters determining energy demand, oil resources and fuel preferences. The contribution of these factors is also scenario-dependent. [Copyright &y& Elsevier]

How can dangerous interference with the climate system be avoided? Science can help decision-makers answer this political question. Ear- lier publications have focused on the probability of keeping global mean temperature change below certain thresholds by stabilizing greenhouse gas concentrations at particular levels. We compare the results of such ‘stabilization profiles’ with a set of ‘peaking profiles’ that reduce emissions further after stabilization and thus result in a concentration peak. Given the inertia in the climate system, stabilization profiles lead to ongoing warming beyond 2100 until the temperature reaches equilibrium. This warming partly can be pre- vented for peaking profiles. In this way, these profiles can increase the likelihood of achieving temperature thresholds by 10-20% com- pared with the likelihood for the associated stabilization profiles. Because the additional mitigation efforts and thus costs for peaking profiles lie mainly beyond 2100, peaking profiles achieving temperature thresholds with the same likelihood as the original stabilization profile, but at considerably lower cost (up to 40%), can be identified. The magnitude of the cost reductions depends on the assumptions on discounting. Peaking profiles and overshoot profiles with a limited overshoot may, in particular, play an important role in making more ambitious climate targets feasible. [ABSTRACT FROM AUTHOR]

A methodology is presented here to assess the potential long-term contribution of non-CO2 greenhouse gases in mitigation scenarios. The analysis shows the future development of the mitigation potential of non-CO2 gases (as a function of changes in technology and implementation barriers) to represent a crucial parameter for the overall costs of mitigation scenarios. The recently developed marginal abatement cost curves for 2010 in the EMF-21 project are taken as the starting point. First-order estimates were made of the future maximum attainable reduction potentials and costs on the basis of available literature. The set of MAC curves developed was used in a multi-gas analysis for stabilising greenhouse gas concentrations at 550ppm CO2-equivalent. Including future development for the non-CO2 mitigation options not only increases their mitigation potential but also lowers the overall costs compared to situations where no development is assumed (3–21% lower in 2050 and 4–26% lower in 2100 in our analysis). Along with the fluorinated gases, energy-related methane emissions make up the largest share in total non-CO2 abatement potential as they represent a large emission source and have a large potential for reduction (towards 90% compared to baseline in 2100). Most methane and nitrous oxide emissions from landuse-related sources are less simple to abate, with an estimated abatement potential in 2100 of around 60% and 40%, respectively. [Copyright &y& Elsevier]

The article focuses on the effect of exchange rates on emission scenarios. These scenarios are aimed to predict the trends of future greenhouse gas emissions and their driving forces. Six different integrated assessment models have been used for the development of emission scenarios. The economic growth is reported in U.S. dollars using market-exchange rates (MER) in most of the scenarios. MER-based economic projections has been criticized by various researchers. They argue that the actual welfare in different regions can be compared properly only by using purchasing power parities.

The greenhouse gas emissions scenarios published by the IPCC in the Special Report on Emission Scenarios (SRES) continue to serve as a primary basis for assessing future climate change and possible response strategies. These scenarios were developed between 1996 and 1999 and sufficient time has now passed to make it worth examining their consistency with more recent data and projections. The comparison performed in this paper includes population, GDP, energy use, and emissions of CO2, non-CO2 gases and sulfur. We find the SRES scenarios to be largely consistent with historical data for the 1990-2000 period and with recent projections. Exceptions to this general observation include (1) in the long-term, relatively high population growth assumptions in some regions, particularly in the A2 scenario; (2) in the medium-term, relatively high economic growth assumptions in the LAM (Latin America, Africa and Middle East) region in the A1 scenario; (3) in the short-term, CO2 emissions projections in Al that are somewhat higher than the range of current scenarios; and (4) substantially higher sulfur emissions in some scenarios than in historical data and recent projections. In conclusion, given the relatively small inconsistencies for use as global scenarios there seems to be no immediate need for a large-scale IPCC-led update of the SRES scenarios that is solely based on the SRES scenario performance vis-a-vis data for the 1990-2000 period and/or more recent projections. Based on reported findings, individual research teams could make, and in some cases already have made, useful updates of the scenarios. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop consistent scenarios of emissions, climate change and regional air pollution to enable an integrated analysis of the linkage between climate change and regional air pollution in Europe. An integrated modeling framework was developed for this purpose. The framework integrates state-of-the-art models and concepts from the area of climate change and regional air pollution and was supplemented by new modules (e.g. modeling long-term NH3 emissions in Europe, modeling dispersion and transformation of air pollutants under climate change).Consistent climate and air pollution policies were derived, both driven by the desire to achieve certain environmental goals. According to an analysis of scenarios with various combinations of climate and regional air pollution policies the quantitatively most relevant interactions are the effect of climate change policies on the energy mix and the resulting air pollution emissions. In the long-term the global SO2 emissions are expected to decrease (again), accordingly their effect on climate will be minor. Tentatively it can be concluded that for regional air pollution the development of the air pollutant emissions is more important than the effect of climate change on the dispersion and chemical transformation of air pollutants. [Copyright &y& Elsevier]

• It is essential to reassess the relevance of emissions scenarios with with long-term developments regularly. • 'IPCC scenarios' did not systematically over-/underestimate historical global emissions. • Historical global emissions followed a medium–high emissions pathway well within scenarios ranges. • Most scenarios overestimated OECD but underestimated non-OECD CO 2 and GDP growth. • Adjusting SSP-BL "non-biomass renewables" & "nuclear" may be relevant for future updates. • We find six overall periods of fast/slow CO 2 growth (1960-2020), highlighting differences between long- vs. short-term evaluations. Long-term emissions scenarios have served as the primary basis for assessing future climate change and response strategies. Therefore, it is important to regularly reassess the relevance of emissions scenarios in light of changing global circumstances and compare them with long-term developments to determine if they are still plausible, considering the newest insights. Four scenario series, SA90, IS92, SRES, and RCP/SSP, were central in the scenario-based literature informing the five Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) and the sixth assessment cycle. Here we analyze the historical trends of carbon dioxide (CO2) emissions from fossil fuel combustion and industry and emissions drivers between 1960 and 2017. We then compare the emission scenario series with historical trends for the period 1990–2017/2018. The results show that historical trends are quite consistent with medium scenarios in each series. As a result, they can be regarded as valid inputs for past and future analyses of climate change and impacts. Global CO2 emissions 1960–2018 (and 1990–2018) comprised six (and three) overall subperiods of emissions growth significantly higher and lower than average. Historically, CO2 emissions (in absolute numbers and growth rate) are tightly coupled with primary energy and indirectly with GDP. Global emissions generally followed a medium-high pathway, captured by "middle-of-the-road" scenario narratives in the earlier series, and by combinations of "global-sustainability" and "middle-of-the-road" narratives in the most recent series (SRES and SSP-baselines). Historical non-OECD trends were best captured by "rapid-growth" and "regional-competition" scenarios, while OECD trends were close to regional-sustainability and global-sustainability scenarios. Areas where the emissions scenarios captured the historical trends less well, are renewable and nuclear primary energy supply. The fact that the actual historical development is consistent with rapid-growth narratives in the non-OECD regions might have important implications for future greenhouse gas emissions and associated climatic change. [ABSTRACT FROM AUTHOR]

A correction to the article "The contribution of N2O to the greenhouse gas balance of first-generation biofuels" that was published in the volume 15, 2010 issue is presented.