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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.

One of the most fundamental questions surrounding the new Paris Agreement is whether countries’ proposals to reduce GHG emissions after 2020 are equally ambitious, considering differences in circumstances between countries. We review a variety of approaches to assess the ambition of the GHG emission reduction proposals by countries. The approaches are applied illustratively to the mitigation part of the post-2020 climate proposals (nationally determined contributions, or NDCs) by China, the EU, and the US. The analysis reveals several clear trends, even though the results differ per individual assessment approach. We recommend that such a comprehensive ambition assessment framework, employing a large variety of approaches, is used in the future to capture a wide spectrum of perspectives on ambition. POLICY RELEVANCE Assessing the ambition of the national climate proposals is particularly important as the Paris Agreement asks for regular reviews of national contributions, keeping in mind that countries raise their ambition over time. Such an assessment will be an important part of the regular global stocktake that will take place every five years, starting with a ‘light’ version in 2018. However, comprehensive methods to assess the proposals are lacking. This article provides such a comprehensive assessment framework.

This article shows the potential impact on global GHG emissions in 2030, if all countries were to implement sectoral climate policies similar to successful examples already implemented elsewhere. This assessment was represented in the IMAGE and GLOBIOM/G4M models by replicating the impact of successful national policies at the sector level in all world regions. The first step was to select successful policies in nine policy areas. In the second step, the impact on the energy and land-use systems or GHG emissions was identified and translated into model parameters, assuming that it would be possible to translate the impacts of the policies to other countries. As a result, projected annual GHG emission levels would be about 50 GtCO2e by 2030 (2% above 2010 levels), compared to the 60 GtCO2e in the ‘current policies’ scenario. Most reductions are achieved in the electricity sector through expanding renewable energy, followed by the reduction of fluorinated gases, reducing venting and flaring in oil and gas production, and improving industry efficiency. Materializing the calculated mitigation potential might not be as straightforward given different country priorities, policy preferences and circumstances. Key policy insightsConsiderable emissions reductions globally would be possible, if a selection of successful policies were replicated and implemented in all countries worldwide.This would significantly reduce, but not close, the emissions gap with a 2°C pathway.From the selection of successful policies evaluated in this study, those implemented in the sector ‘electricity supply’ have the highest impact on global emissions compared to the ‘current policies’ scenario.Replicating the impact of these policies worldwide could lead to emission and energy trends in the renewable electricity, passenger transport, industry (including fluorinated gases) and buildings sector, that are close to those in a 2°C scenario.Using successful policies and translating these to policy impact per sector is a more reality-based alternative to most mitigation pathways, which need to make theoretical assumptions on policy cost-effectiveness.

By 15 December 2015, 187 countries had submitted their Intended Nationally Determined Contributions (INDCs) summarising their climate actions after 2020 in the context of the Paris Agreement. We used a unified framework to assess the mitigation components of INDCs covering 105 countries (representing approximately 91 % of global greenhouse gas emissions in 2012) with a special focus on the G20 economies. We estimated the required reduction effort by comparing the greenhouse gas emission targets implied by the INDCs with the projected levels resulting from current mitigation policies. The resulting projected global reduction effort amounts to approximately 4–6 GtCO2eq by 2030, of which the G20 economies are responsible for the largest share, in particular Brazil, China, the EU, and the United States. Despite these reductions, the global and G20 emission level is still projected to be higher in 2030 than it was in 2010. We compared the ambition levels of individual INDCs by analysing various indicators. Our analysis shows, for instance, that INDCs imply that greenhouse gas emissions of Brazil, Indonesia, Mexico, and South Korea peak before 2025, and of China, India and South Africa by 2030 or later.

By 15 December 2015, 187 countries had submitted their Intended Nationally Determined Contributions (INDCs) summarising their climate actions after 2020 in the context of the Paris Agreement. We used a unified framework to assess the mitigation components of INDCs covering 105 countries (representing approximately 91 % of global greenhouse gas emissions in 2012) with a special focus on the G20 economies. We estimated the required reduction effort by comparing the greenhouse gas emission targets implied by the INDCs with the projected levels resulting from current mitigation policies. The resulting projected global reduction effort amounts to approximately 4–6 GtCO2eq by 2030, of which the G20 economies are responsible for the largest share, in particular Brazil, China, the EU, and the United States. Despite these reductions, the global and G20 emission level is still projected to be higher in 2030 than it was in 2010. We compared the ambition levels of individual INDCs by analysing various indicators. Our analysis shows, for instance, that INDCs imply that greenhouse gas emissions of Brazil, Indonesia, Mexico, and South Korea peak before 2025, and of China, India and South Africa by 2030 or later.

In June 2015, China announced its post-2020 reduction targets, its central element being the intention to peak CO2 emissions by 2030 or earlier. China has implemented several policies to reduce its greenhouse gas (GHG) emissions. This study provides emission projections for China up to 2030 given current policies and a selected set of enhanced policies, and compares the results with projected CO2 emission trajectories that are consistent with the announced target for 2030. The projections are based on existing scenarios and energy system and land use model calculations. We project that the 2030 CO2 emission level consistent with a peak in CO2 emissions by 2030 ranges from 11.3 to 11.8 GtCO2. The corresponding total GHG emission level ranges from 13.5 to 14.0 GtCO2e in 2030. Current policies are likely not to be sufficient to achieve the 2030 targets, as our projected total GHG emission level under current policies ranges from 14.7 to 15.4 GtCO2e by 2030. However, an illustrative set of enhancement policy measures, all of which are related to national priorities, leads to projected GHG emission levels from 13.1 to 13.7 GtCO2e by 2030 - and thus below the levels necessary for peaking CO2 emissions before 2030.

In June 2015, China announced its post-2020 reduction targets, its central element being the intention to peak CO2 emissions by 2030 or earlier. China has implemented several policies to reduce its greenhouse gas (GHG) emissions. This study provides emission projections for China up to 2030 given current policies and a selected set of enhanced policies, and compares the results with projected CO2 emission trajectories that are consistent with the announced target for 2030. The projections are based on existing scenarios and energy system and land use model calculations. We project that the 2030 CO2 emission level consistent with a peak in CO2 emissions by 2030 ranges from 11.3 to 11.8 GtCO2. The corresponding total GHG emission level ranges from 13.5 to 14.0 GtCO2e in 2030. Current policies are likely not to be sufficient to achieve the 2030 targets, as our projected total GHG emission level under current policies ranges from 14.7 to 15.4 GtCO2e by 2030. However, an illustrative set of enhancement policy measures, all of which are related to national priorities, leads to projected GHG emission levels from 13.1 to 13.7 GtCO2e by 2030 - and thus below the levels necessary for peaking CO2 emissions before 2030.

Most modelling studies that explore long-term greenhouse gas mitigation scenarios focus on cost-efficient emission pathways towards a certain climate target, like the internationally agreed target to keep global temperature increase below 2 °C compared to pre-industrial levels (the 2 °C climate target). However, different timing of reductions lead to different transient temperature increase over the course of the century and subsequently to differences in the time profiles of not only the mitigation costs but also adaptation costs and residual climate change damage. This study adds to the existing literature by focussing on the implication of these differences for the evaluation of a set of three mitigation scenarios (early action, gradual action and delayed action), all three limiting global temperature increase below 2 °C above pre-industrial levels, using different discount rates. The study shows that the gradual mitigation pathway is, for these discount rates, preferred over early or delayed action in terms of total climate costs and net benefits. The relative costs and benefits of the early or delayed mitigation action scenarios, in contrast, do strongly depend on the discount rate applied. For specific discount rates, these pathways might therefore be preferred for other reasons, such as reducing long-term uncertainty in climate costs by early action.

Greenhouse gas emissions associated with Representative Concentration Pathway RCP2.6 could limit global warming to around or below a 2 °C increase since pre-industrial times. However this scenario implies very large and rapid reductions in both carbon dioxide (CO2) and non-CO2 emissions, and suggests a need to understand available flexibility between how different greenhouse gases might be abated. There is a growing interest in developing a greater understanding of the particular role of shorter lived non-CO2 gases as abatement options. We address this here through a sensitivity study of different methane (CH4) emissions pathways to year 2100 and beyond, by including exchanges with CO2 emissions, and with a focus on related climate and economic advantages and disadvantages. Metrics exist that characterise gas equivalence in terms of climate change effect per tonne emitted. We analyse the implications of CO2 and CH4 emission exchanges under two commonly considered metrics: the 100-yr Global Warming Potential (GWP-100) and Global Temperature Potential (GTP-100). This is whilst keeping CO2-equivalent emissions pathways fixed, based on the standard set of emissions usually associated with RCP2.6. An idealised situation of anthropogenic CH4 emissions being reduced to zero across a period of two decades and with the implementation of such cuts starting almost immediately gives lower warming than for standard RCP2.6 emissions during the 21st and 22nd Century. This is despite exchanging for higher CO2 emissions. Introducing Marginal Abatement Cost (MAC) curves provides an economic assessment of alternative gas reduction strategies. Whilst simpler than utilising full Integrated Assessment Models (IAMs), MAC curves are more transparent for illustrative modelling. The GWP-100 metric places a relatively high value on climate change prevented for methane emission reduction, as compared to an equivalent mass of CO2 reduction. This in combination with the strong non-linearity in MAC curves (moving quickly from relatively cheap removal to emissions difficult to cut at any cost) causes little change under cost minimisation from standard RCP2.6 emissions. This reflects the original development of RCP2.6 standard emissions from similar minimisation. With gas exchange under GTP-100, however, we find much less methane is abated, resulting in higher temperatures, whilst costs are slightly lower. Our results also highlight the point at which greater methane mitigation would become beneficial from both a climate and economic aspect. If by 2030 removal of all methane were to become possible at an average cost less than $1000 per tonne of CH4, then this would be the cheapest option, for GWP-100 metric and our CO2 MAC curve. Critically this would increase the possibility of constraining warming to two degrees.

The thirteenth Conference of the Parties to the United Nations Framework Convention on Climate Change in 2007 decided that developing countries should be compensated for adaptation costs to climate change through the Adaptation Fund (first draft decision of the third session of the conference of the parties serving as the meeting of the parties to the Kyoto Protocol). This shows that adaptation to climate change has become important in international climate negotiations. Today, adaptation is widely recognized as an equally important and complementary response to climate change mitigation (for example, Commission of the European Communities 2007; IPCC 2007a; Agrawala and Fankhauser 2008). Still, relatively little information is available to support more integrated climate policies that focus on both mitigation and adaptation (Klein et al. 2005). In particular, in integrated assessment models that aim at supporting climate policy by analysing their economic and environmental consequences and formulating efficient responses, explicit consideration of adaptation is still in its infancy (Tol 2005; Wilbanks 2005; Agrawala et al. 2008). This chapter tries to fill the gap in integrated assessment models by integrating adaptation and residual damage functions from AD-RICE (de Bruin et al. 2009) with the FAIR model (den Elzen and van Vuuren 2007; Hof et al. 2008). This version of the FAIR model (from now on called AD-FAIR) enables an analysis of the interactions between mitigation, emissions trading, adaptation and residual damages (that is, damages not avoided by adaptation measures) on a global as well as regional scale. Furthermore, adaptation is modelled explicitly as a policy variable, providing insights in the economic consequences of adaptation. This information is vital for effective adaptation governance.

The thirteenth Conference of the Parties to the United Nations Framework Convention on Climate Change in 2007 decided that developing countries should be compensated for adaptation costs to climate change through the Adaptation Fund (first draft decision of the third session of the conference of the parties serving as the meeting of the parties to the Kyoto Protocol). This shows that adaptation to climate change has become important in international climate negotiations. Today, adaptation is widely recognized as an equally important and complementary response to climate change mitigation (for example, Commission of the European Communities 2007; IPCC 2007a; Agrawala and Fankhauser 2008). Still, relatively little information is available to support more integrated climate policies that focus on both mitigation and adaptation (Klein et al. 2005). In particular, in integrated assessment models that aim at supporting climate policy by analysing their economic and environmental consequences and formulating efficient responses, explicit consideration of adaptation is still in its infancy (Tol 2005; Wilbanks 2005; Agrawala et al. 2008). This chapter tries to fill the gap in integrated assessment models by integrating adaptation and residual damage functions from AD-RICE (de Bruin et al. 2009) with the FAIR model (den Elzen and van Vuuren 2007; Hof et al. 2008). This version of the FAIR model (from now on called AD-FAIR) enables an analysis of the interactions between mitigation, emissions trading, adaptation and residual damages (that is, damages not avoided by adaptation measures) on a global as well as regional scale. Furthermore, adaptation is modelled explicitly as a policy variable, providing insights in the economic consequences of adaptation. This information is vital for effective adaptation governance.

This study compares emission pathways aimed at limiting temperature increase to 2°C under varying constraints. In a first set of pathways, the timing of emission reductions is such that over the 2010-2100 period, assuming full participation from 2013 onwards, mitigation costs are minimized. In a second set of pathways, we set emissions in 2020 at a level based on the pledges of the Copenhagen Accord. In the 'Copenhagen Potential' scenario, climate talks result in satisfying conditions linked by countries to their 'most ambitious' proposals. Contrasting, in the 'Copenhagen Current' scenario, climate talks fall short of satisfying the conditions to move beyond current unilateral pledges. We include scenarios with and without the availability of bio-energy in combination with carbon capture and storage. We find that for a 'Copenhagen Potential' scenario, emissions by 2020 are higher (47 GtCO 2eq/yr) than for a least-cost pathway for 2°C (43 GtCO 2eq/yr with a 40-46 GtCO 2eq/yr literature range). In the 'Copenhagen Potential' scenario the 2°C target can still be met with a likely chance, although discounted mitigation costs over 2010-2100 could be 10 to 15 % higher, and up to 60 % in the 2040-2050s, than for least-cost pathways. For the 'Current Copenhagen' scenario, maintaining an equally low probability of exceeding 2°C becomes infeasible in our model, implying higher costs due to higher climate risks. We conclude that there is some flexibility in terms of 2020 emissions compared to the optimal pathways but this is limited. The 2020 emission level represents a trade-off between short-term emission reductions and long-term dependence on rapid reductions through specific technologies (like negative emission reductions). Higher 2020 emissions lead to higher overall costs and reduced long-term flexibility, both leading to a higher risk of failing to hold warming below 2°C.

As part of the Copenhagen Accord, individual countries have submitted greenhouse gas reduction proposals for the year 2020. This paper analyses the implications for emission reductions, the carbon price, and abatement costs of these submissions. The submissions of theAnnex I (industrialised) countries are estimated tolead toa total reductiontarget of 12¿18% below 1990 levels. The submissions of the seven major emerging economies are estimated to lead to an 11¿14% reduction belowbaseline emissions, depending on international (financial) support. Global abatement costs in 2020 are estimated at about USD 60¿100 billion, assuming that at leasttwo-thirdsofAnnexIemissionreductiontargetsneedtobeachieveddomestically. ThelargestshareofthesecostsareincurredbyAnnexIcountries,althoughthecostsasshareof GDP are similar for Annex I as a group and the seven emerging economies as a group, even when assuming substantial international transfers from Annex I countries to the emerging economies to finance their abatement costs. If the restriction of achieving two-thirds of the emission reduction target domestically is abandoned, itwouldmore than double the international carbon price and at the same time reduce global abatement costs by almost 25%., JRC.H.2-Climate change and air quality