Zero carbon energy system pathways for Ireland consistent with the Paris Agreement

The Paris Agreement is the last hope to keep global temperature rise below 2°C. The consensus agrees to holding the increase in global average temperature to well below 2°C above pre-industrial levels, and to aim for 1.5°C. Each Party’s successive nationally determined contribution (NDC) will represent a progression beyond the party’s then current NDC, and reflect its highest possible ambition. Using Ireland as a test case, we show that increased mitigation ambition is required to meet the Paris Agreement goals in contrast to current EU policy goals of an 80–95% reduction by 2050. For the 1.5°C consistent carbon budgets, the technically feasible scenarios' abatement costs rise to greater than €8,100/tCO₂ by 2050. The greatest economic impact is in the short term. Annual GDP growth rates in the period to 2020 reduce from 4% to 2.2% in the 1.5°C scenario. While aiming for net zero emissions beyond 2050, investment decisions in the next 5–10 years are critical to prevent carbon lock-in.

Key policy insights

• Economic growth can be maintained in Ireland while rapidly decarbonizing the energy system.

• The social cost of carbon needs to be included as standard in valuation of infrastructure investment planning, both by government finance departments and private investors.

• Technological feasibility is not the limiting factor in achieving rapid deep decarbonization.

• Immediate increased decarbonization ambition over the next 3–5 years is critical to achieve the Paris Agreement goals, acknowledging the current 80–95% reduction target is not consistent with temperature goals of ‘well below’ 2°C and pursuing 1.5°C.

• Applying carbon budgets to the energy system results in non-linear CO₂ emissions reductions over time, which contrast with current EU policy targets, and the implied optimal climate policy and mitigation investment strategy.

     

Convergence of per capita carbon dioxide emissions: implications and meta-analysis

There is a rich empirical literature testing whether per capita carbon dioxide emissions tend to converge over time and across countries. This article provides a meta-analysis of the results from this research, and discusses how carbon emissions convergence may be understood in, for instance, the presence of international knowledge spillovers and policy convergence. The results display evidence of either divergence or persistent gaps at the global level, but convergence of per capita carbon dioxide emissions between richer industrialized countries. However, the results appear sensitive to the choice of data sample and choice of convergence concept, e.g. stochastic convergence versus β-convergence. Moreover, peer-reviewed studies have a higher likelihood of reporting convergence in carbon dioxide emissions compared to non-refereed work.

POLICY RELEVANCE

The empirical basis for an egalitarian rule of equal emissions per capita in the design of global climate agreements is not solid; this supports the need to move beyond single allocation rules, and increase knowledge about the impacts of combined scenarios. However, even in the context of the 2015 Paris Agreement with its emphasis on voluntary contributions and ‘national circumstances’, different equity-based principles could serve as useful points of reference for how the remaining carbon budget should be allocated.     

Greenhouse gas emissions from global cities under SSP/RCP scenarios, 1990 to 2100

Projections of greenhouse gas (GHG) emissions are critical to enable a better understanding and anticipation of future climate change under different socio-economic conditions and mitigation strategies. The climate projections and scenarios assessed by the Intergovernmental Panel on Climate Change, following the Shared Socioeconomic Pathway (SSP)-Representative Concentration Pathway (RCP) framework, have provided a rich understanding of the constraints and opportunities for policy action. However, the current emissions scenarios lack an explicit treatment of urban emissions within the global context. Given the pace and scale of urbanization, with global urban populations expected to increase from about 4.4 billion today to about 7 billion by 2050, there is an urgent need to fill this knowledge gap. Here, we estimate the share of global GHG emissions driven by urban areas from 1990 to 2100 based on the SSP-RCP framework. The urban consumption-based GHG emissions are presented in five regional aggregates and based on a combination of the urban population share, 2015 urban per capita CO₂eq carbon footprint, SSP-based national CO₂eq emissions, and recent analysis of urban per capita CO₂eq trends. We find that urban areas account for the majority of global GHG emissions in 2015 (61.8%). Moreover, the urban share of global GHG emissions progressively increases into the future, exceeding 80% in some scenarios by the end of the century. The combined urban areas in Asia and Developing Pacific, and Developed Countries account for 65.0% to 73.3% of cumulative urban consumption-based emissions between 2020 and 2100 across the scenarios. Given these dominant roles, we describe the implications for potential urban mitigation in each of the scenario narratives in order to meet the goal of climate neutrality within this century.     

National contributions to climate change mitigation from agriculture: allocating a global target

Globally, agriculture and related land use change contributed about 17% of the world’s anthropogenic GHG emissions in 2010 (8.4 GtCO₂e yr^?1), making GHG mitigation in the agriculture sector critical to meeting the Paris Agreement’s 2°C goal. This article proposes a range of country-level targets for mitigation of agricultural emissions by allocating a global target according to five approaches to effort-sharing for climate change mitigation: responsibility, capability, equality, responsibility-capability-need and equal cumulative per capita emissions. Allocating mitigation targets according to responsibility for total historical emissions or capability to mitigate assigned large targets for agricultural emission reductions to North America, Europe and China. Targets based on responsibility for historical agricultural emissions resulted in a relatively even distribution of targets among countries and regions. Meanwhile, targets based on equal future agricultural emissions per capita or equal per capita cumulative emissions assigned very large mitigation targets to countries with large agricultural economies, while allowing some densely populated countries to increase agricultural emissions. There is no single ‘correct’ framework for allocating a global mitigation goal. Instead, using these approaches as a set provides a transparent, scientific basis for countries to inform and help assess the significance of their commitments to reducing emissions from the agriculture sector.

Key policy insights

• Meeting the Paris Agreement 2°C goal will require global mitigation of agricultural non-CO₂ emissions of approximately 1 GtCO₂e yr^?1 by 2030.

• Allocating this 1 GtCO₂e yr^?1 according to various effort-sharing approaches, it is found that countries will need to mitigate agricultural business-as-usual emissions in 2030 by a median of 10%. Targets vary widely with criteria used for allocation.

• The targets calculated here are in line with the ambition of the few countries (primarily in Africa) that included mitigation targets for the agriculture sector in their (Intended) Nationally Determined Contributions.

• For agriculture to contribute to meeting the 2°C or 1.5°C targets, countries will need to be ambitious in pursuing emission reductions. Technology development and transfer will be particularly important.

     

Global forest products markets and forest sector carbon impacts of projected sea level rise

Sea level rise (SLR) is among the climate-change-related problems of greatest concern, threatening the lives and property of coastal residents and generating far-reaching economic and ecological impacts. We project that SLR will lead to an increase in the rate of new housing construction to replace destroyed structures, impact global wood products supply and demand conditions, and cause changes in global forest sector carbon mitigation potential. Findings indicate that 71 million new units will be built by 2050 to accommodate the SLR-affected global population. More than two-thirds of these new units are projected to be in Asia. The estimated extra wood products needed to build these new residential units is 1,659 million m³, assuming that all these structures would be built mainly with wood, representing a 4 % increase in total wood consumption, compared to projected reference level global wood products consumption. Increased timber removals to meet this higher construction wood demand (alternative scenario) is shown to deplete global forest carbon by 2 % by 2050 compared to the reference scenario. However, all such projected declines in forest biomass carbon could be more than offset by increased carbon sequestration in harvested wood products, avoided emissions due to substitution of wood for non-wood materials in construction, and biomass regrowth on forestland by 2050, with an estimated net emissions reduction benefit of 0.47 tCO₂e/tCO₂e of extra wood used in SLR-related new houses over 30 years. The global net emissions reduction benefit increased to 2.13 tCO₂e/tCO₂e of extra wood when price-induced changes in forest land area were included.     

International and national climate policies for aviation: a review

Aviation constitutes about 2.5% of all energy-related CO₂ emissions and in addition there are non-CO₂ effects. In 2016, the ICAO decided to implement a Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) and in 2017 the EU decided on faster emission reductions in its Emissions Trading System (EU ETS), which since 2012 includes the aviation sector. The effects of these policies on the expected development of air travel emissions from 2017 to 2030 have been analyzed. For the sample country Sweden, the analysis shows that when emissions reductions in other sectors are attributed to the aviation sector as a result of the EU ETS and CORSIA, carbon emissions are expected to reduce by ?0.8% per year (however if non-CO₂ emissions are included in the analysis, then emissions will increase). This is much less than what is needed to achieve the 2°C target. Our analysis of potential national aviation policy instruments shows that there are legally feasible options that could mitigate emissions in addition to the EU ETS and CORSIA. Distance-based air passenger taxes are common among EU Member States and through increased ticket prices these taxes can reduce demand for air travel and thus reduce emissions. Tax on jet fuel is an option for domestic aviation and for international aviation if bilateral agreements are concluded. A quota obligation for biofuels is a third option.

Key policy insights

• Existing international climate policies for aviation will not deliver any major emission reductions.

• Policymakers who want to significantly push the aviation sector to contribute to meeting the 2°C target need to work towards putting in place tougher international policy instruments in the long term, and simultaneously implement temporary national policy instruments in the near-term.

• Distance-based air passenger taxes, carbon taxes on jet fuel and quota obligations for biofuels are available national policy options; if they are gradually increased, and harmonized with other countries, they can help to significantly reduce emissions.

     

Designing air ticket taxes for climate change mitigation: insights from a Swedish valuation study

Research on air travellers’ willingness to pay (WTP) for climate change mitigation has focussed on voluntary emissions offsetting so far. This approach overlooks policy relevant knowledge as it does not consider that people may value public goods higher if they are certain that others also contribute. To account for potential differences, this study investigates Swedish adults’ WTP for a mandatory air ticket surcharge both for short- and long-distance flights. Additionally, policy relevant factors influencing WTP for air travel emissions reductions were investigated. The results suggest that mean WTP is higher in the low-cost setting associated with short-distance flights (495 SEK/ tCO₂; 50 EUR/ tCO₂) than for long-distance flights (295 SEK/ tCO₂; 30 EUR/t CO₂). The respondents were more likely to be willing to pay the air ticket tax if they were not frequent flyers, if they were women, had a left political view, if they had a sense of responsibility for their emissions and if they preferred earmarking revenues from the tax for climate change mitigation and sustainable transport projects.

Key policy insights

• A mandatory air ticket tax is a viable policy option that might receive majority support among the population.

• While a carbon-based air ticket tax promises to be an effective tool to generate revenues, its potential steering effect appears to be lower for low cost contexts (short-distance flights) than for high cost contexts (long-distance flights).

• Policy consistency regarding the tax base and its revenue use may increase public acceptability of (higher) air ticket taxes. Earmarking revenues is clearly preferred to tax recycling or general budget use.

• Insights about the personal drivers behind WTP for emissions reductions from air travel can help to inform targeting and segmentation of policy interventions.

     

Achieving development and mitigation objectives through a decarbonization development pathway in South Africa

Achieving the international 2 °C limit climate policy requires stringent reductions in GHG emissions by mid-century, with some countries simultaneously facing development-related challenges. South Africa is a middle-income developing country with high rates of unemployment and high levels of poverty, as well as an emissions-intensive economy. South Africa takes into account an assessment of what a fair contribution to reducing global emissions might be, and is committed to a ‘peak, plateau and decline' emissions trajectory with absolute emissions specified for 2025 and 2030, while noting the need to address development imperatives. This work utilizes an economy-wide computable general equilibrium model (e-SAGE) linked to an energy-system optimization model (TIMES) to explore improving development metrics within a 14 GtCO₂e cumulative energy sector carbon constraint through to 2050 for South Africa. The electricity sector decarbonizes by retiring coal-fired power plants or replacing with concentrated solar power, solar photovoltaics and wind generation. Industry and tertiary-sector growth remains strong throughout the time period, with reduced energy intensity via fuel-switching and efficiency improvements. From 2010 to 2050, the model results in the unemployment rate decreasing from 25% to 12%, and the percentage of people living below the poverty line decreasing from 49% to 18%. Total energy GHG emissions were reduced by 39% and per capita emissions decreased by 62%.

Policy relevance

Lower poverty and inequality are goals that cannot be subordinated to lower GHG emissions. Policy documents in South Africa outline objectives such as reducing poverty and inequality with a key focus on education and employment. In its climate policy and Intended Nationally Determined Contribution (INDC), South Africa is committed to a peak, plateau and decline GHG emissions trajectory. As in many developing countries, these policy goals require major transformations in the energy system while simultaneously increasing affordable access to safe and convenient energy services for those living in energy poverty. The modelled scenario in this work focuses on employment and poverty reduction under a carbon constraint, a novel combination with results that can provide information for a holistic climate and development policy framework. This study has focused on the long term, which is important in generating clear policy signals for the necessary large-scale investments.     

The population structural transition effect on rising per capita CO2 emissions: evidence from China

ABSTRACT

The per capita CO₂ emissions (PCCE) of many developing countries like China have been rising faster than total CO₂ emissions, and display spatial divergence. Such temporal growth and spatial divergence will have a significant influence on efforts to mitigate CO₂ emissions. Given the research gap on the impact of the structural transition in population on PCCE, we constructed an econometric model using the dynamic panel method. The results reveal that the population structural transition has a significant nonlinear impact on PCCE, as the rate of population growth in China decelerates. Both demographic ageing and urban-rural migration have a stronger impact on PCCE than other factors. This effect, however, decreases beyond a certain threshold. An increase in the number of households due to urbanization and family downsizing has resulted in a positive effect on PCCE, without a threshold turning point. The research also finds that an increased share of the service sector in employment can reduce PCCE only if the sector employs more than 31.56% of the total employed population. Overall, these findings indicate that policymakers should pay attention to the prominence of the demographic structural transition for effective climate policy.

Key policy insights

• Policymakers should address rising per capita carbon emissions (PCCE) and their spatial divergence in future climate policies, not just total CO₂ emissions.

• The transitioning demographics of ageing and urbanization in China show a nonlinear, inverted U-shaped effect on PCCE instead of a continuously positive effect.

• Based on the nonlinear effect of employment structure on PCCE, policymakers should focus on the relationship between the structural transition of the economy and PCCE in future climate mitigation policies.

     

Consumption-based GHG emission accounting: a UK case study

Global GHG emissions continue to rise, with nearly a quarter of it due to trade that is not currently captured within global climate policy. In the context of current trade patterns and limited global cooperation on climate change, the feasibility of consumption-based emissions accounting to contribute to a more comprehensive (national) policy framework in the UK is investigated. Consumption-based emissions results for the UK from a range of models are presented, their technical robustness is assessed, and their potential application in national climate policy is examined using examples of policies designed to reduce carbon leakage and to address high levels of consumption. It is shown that there is a need to include consumption-based emissions as a complementary indicator to the current approach of measuring territorial emissions. Methods are shown to be robust enough to measure progress on climate change and develop and inform mitigation policy. Finally, some suggestions are made for future policy-oriented research in the area of consumption-based accounting that will facilitate its application to policy.

Policy relevance

Emissions embodied in trade are rapidly increasing and there is thus a growing gap between production emissions and the emissions associated with consumption. This is a growing concern due to the absence of a global cap and significant variation in country-level mitigation ambitions. Robust measurements of consumption-based emissions are possible and provide new insights into policy options. This includes trade-related policy (e.g. border carbon adjustments) and domestic policies (e.g. resource efficiency strategies). As climate policy targets deepen, there is a need for a broad range of policy options in addition to production and technological solutions. Consumption-based emissions are complementary to production-based emissions inventories, which are still the most accurate estimate for aggregated emissions at the global level. However, without consumption-based approaches, territorial emissions alone will not provide a complete picture of progress in regional and national emissions reduction.     

What if negative emission technologies fail at scale? Implications of the Paris Agreement for big emitting nations

A cumulative emissions approach is increasingly used to inform mitigation policy. However, there are different interpretations of what ‘2°C’ implies. Here it is argued that cost-optimization models, commonly used to inform policy, typically underplay the urgency of 2°C mitigation. The alignment within many scenarios of optimistic assumptions on negative emissions technologies (NETs), with implausibly early peak emission dates and incremental short-term mitigation, delivers outcomes commensurate with 2°C commitments. In contrast, considering equity and socio-technical barriers to change, suggests a more challenging short-term agenda. To understand these different interpretations, short-term CO₂ trends of the largest CO₂ emitters, are assessed in relation to a constrained CO₂ budget, coupled with a ‘what if’ assumption that negative emissions technologies fail at scale. The outcomes raise profound questions around high-level framings of mitigation policy. The article concludes that applying even weak equity criteria, challenges the feasibility of maintaining a 50% chance of avoiding 2°C without urgent mitigation efforts in the short-term. This highlights a need for greater engagement with: (1) the equity dimension of the Paris Agreement, (2) the sensitivity of constrained carbon budgets to short-term trends and (3) the climate risks for society posed by an almost ubiquitous inclusion of NETs within 2°C scenarios.

POLICY RELEVANCE

Since the Paris meeting, there is increased awareness that most policy ‘solutions’ commensurate with 2°C include widespread deployment of negative emissions technologies (NETs). Yet much less is understood about that option’s feasibility, compared with near-term efforts to curb energy demand. Moreover, the many different ways in which key information is synthesized for policy makers, clouds the ability of policy makers to make informed decisions. This article presents an alternative approach to consider what the Paris Agreement implies, if NETs are unable to deliver more carbon sinks than sources. It illustrates the scale of the climate challenge for policy makers, particularly if the Agreement’s aim to address ‘equity’ is accounted for. Here it is argued that much more attention needs to be paid to what CO₂ reductions can be achieved in the short-term, rather than taking a risk that could render the Paris Agreement’s policy goals unachievable.     

China's role in attaining the global 2°C target

In the recent climate change negotiations it was declared that the increase in global temperature should be kept below 2°C by 2100, relative to pre-industrial levels. China's CO₂ emissions from energy and cement processes already account for nearly 24% of global emissions, a trend that is expected to keep increasing. Thus the role of China in global GHG mitigation is crucial. A scenario analysis of China's CO₂ emissions is presented here and the feasibility of China reaching a low-carbon scenario is discussed. The results suggest that recent and continued technological progress will make it possible for China to limit its CO₂ emissions and for these emissions to peak before 2025 and therefore that the global 2°C target can be achieved.

Policy relevance

In signing the Copenhagen Accord, China agreed to the global 2°C target. Results from this article could be used to justify low-carbon development policies and negotiations. While many still doubt the feasibility of a low-carbon pathway to support the global 2°C target, the results suggest that such a pathway can be realistically achieved. This conclusion should increase confidence and guide the policy framework further to make possible China's low-carbon development. Related policies and measures, such as renewable energy development, energy efficiency, economic structure optimization, technology innovation, low-carbon investment, and carbon capture and storage (CCS) development, should be further enhanced. Furthermore, China can play a larger role in the international negotiations process. In the global context, the 2°C target could be reaffirmed and a global regime on an emissions mitigation protocol could be framed with countries’ emissions target up to 2050.     

The Regensburg Model: reference values for the (I)NDCs based on converging per capita emissions†

A core question still remains after the Paris Agreement: who receives how much of the remaining CO₂ budget (resource/burden/effort sharing), so that the increase in the global average temperature is kept to well below 2°C above pre-industrial levels? If converging per capita emissions serve as a possible answer to this question, the discussion focuses primarily on the approach ‘Contraction and Convergence’ (C&C). The Regensburg Model now offers a further option for the mathematical implementation of converging per capita emissions. The authors identify features common to C&C and differences from C&C. They show that, of the convergence models they examined, the Regensburg Model is the most favourable option for industrialized countries.

Policy relevance

In politics, the concept of converging per capita emissions is often accepted at the abstract level. Civil society in particular can then take politicians at their word wherever they take values calculated using the Regensburg Model as points of reference; then prosperous developed countries in particular whose nationally determined contributions do not come up even to these reference values will find it difficult to justify their contributions.     

Implications of global emission policy scenarios for domestic agriculture: a New Zealand case study

Agricultural GHG mitigation policies are important if ambitious climate change goals are to be achieved, and have the potential to significantly lower global mitigation costs [Reisinger, A., Havlik, P., Riahi, K., van Vliet, O., Obersteiner, M., & Herrero, M. (2013). Implications of alternative metrics for global mitigation costs and greenhouse gas emissions from agriculture. Climatic Change, 117, 677–690]. In the post-Paris world of ‘nationally determined contributions’ to mitigation, the prospects for agricultural mitigation policies may rest on whether they are in the national economic interest of large agricultural producers. New Zealand is a major exporter of livestock products; this article uses New Zealand as a case study to consider the policy implications of three global policy scenarios at the global, national and farm levels. Building on global modelling, a model dairy farm and a model sheep and beef farm are used to estimate the changes in profit when agricultural emissions are priced and mitigated globally or not, and priced domestically or not, in 2020. Related to these scenarios is the metric or GHG exchange rate. Most livestock emissions are non-CO₂, with methane being particularly sensitive to the choice of metric. The results provide evidence that farm profitability is more sensitive to differing international policy scenarios than national economic welfare. The impact of the choice of metric is not as great as the impact of whether other countries mitigate agricultural emissions or not. Livestock farmers do best when agricultural emissions are not priced, as livestock commodity prices rise significantly due to competition for land from forestry. However, efficient farmers may still see a rise in profitability when agricultural emissions are fully priced worldwide.

Policy relevance

Exempting agricultural emissions from mitigation significantly increases the costs of limiting warming to 2 °C, placing the burden on other sectors. However, there may be a large impact on farmers if agricultural emissions are priced domestically when other countries are not doing the same. The impacts of global and national climate policies on farmers need to be better understood in order for climate policies to be politically sustainable. Transitional assistance that is not linked to emission levels could help, as long as the incentives to mitigate are maintained. In the long run, efficient farmers may benefit from climate policy; international efforts should focus on mitigation options and effective domestic policy development, rather than on metrics.     

Potential impact of albedo incorporation in boreal forest sector climate change policy effectiveness

Forests have an important role to play in climate change mitigation through carbon sequestration and wood supply. However, the lower albedo of mature forests compared to bare land implies that focusing only on GHG accounting may lead to biased estimates of forestry's total climatic impacts. An economic model with a high degree of detail of the Norwegian forestry and forest industries is used to simulate GHG fluxes and albedo impacts for the next decades. Albedo is incorporated in a carbon tax/subsidy scheme in the Norwegian forest sector using a partial, spatial equilibrium model. While a price of EU€100/tCO₂e that targets GHG fluxes only results in reduced harvests, the same price including albedo leads to harvest levels that are five times higher in the first five years, with 39% of the national productive forest land base being cleared. The results suggest that policies that only consider GHG fluxes and ignore changes in albedo will not lead to an optimal use of the forest sector for climate change mitigation.

Policy relevance

Bare land reflects a larger share of incoming solar energy than dense forest and thus has higher albedo. Earlier research has suggested that changes in albedo caused by management of boreal forest may be as important as carbon fluxes for the forest's overall global warming impacts. The presented analysis is the first attempt to link albedo to national-scale forest climate policies. A policy with subsidies to forest owners that generate carbon sequestration and taxes levied on carbon emissions leads to a reduced forest harvest. However, including albedo in the policy alongside carbon fluxes yields very different results, causing initial harvest levels to increase substantially. The inclusion of albedo impacts will make harvests more beneficial for climate change mitigation as compared to a carbon-only policy. Hence, it is likely that carbon policies that ignore albedo will not lead to optimal forest management for climate change mitigation.     

Global impact of a climate treaty if the Human Development Index replaces GDP as a welfare proxy

This study explores the implications of shifting the narrative of climate policy evaluation from one of costs/benefits or economic growth to a message of improving social welfare. Focusing on the costs of mitigation and the associated impacts on gross domestic product (GDP) may translate into a widespread concern that a climate agreement will be very costly. This article considers the well-known Human Development Index (HDI) as an alternative criterion for judging the welfare effects of climate policy. We estimate what the maximum possible annual average increase in HDI welfare per tons of CO₂ would be within the carbon budget associated with limiting warming to 2°C over the period 2015–2050. Emission pathways are determined by a policy that allows the HDI of poor countries and their emissions to increase under a business-as-usual development path, while countries with a high HDI value (>0.8) have to restrain their emissions to ensure that the global temperature rise does not exceed 2°C. For comparison, the well-known multi-regional RICE model is used to assess GDP growth under the same climate change policy goals.

Policy relevance

This is the first study that shifts the narrative of climate policy evaluation from one of GDP growth to a message of improving social welfare, as captured by the HDI. This could make it easier for political leaders and climate negotiators to publicly commit themselves to ambitious carbon emission reduction goals, such as limiting global warming to 2°C, as in the (non-binding) agreement made at COP 21 in Paris in 2015. We find that if impacts are framed in terms of growth in HDI per t CO₂ emission per capita instead of in GDP, the HDI of poor countries and their emissions are allowed to increase under a business-as-usual development path, whereas countries with a high HDI (>0.8) must control emissions so that global temperature rise remains within 2°C. Importantly, a climate agreement is more attractive for rich countries under the HDI than the GDP frame. This is good news, as these countries have to make the major contribution to emissions reductions.     

Carbon taxes and greenhouse gas emissions trading systems: what have we learned?

Systematic evidence relating to the performance of carbon pricing – carbon taxes and greenhouse gas (GHG) emissions trading systems (ETSs) – is sparse. In 2015, 17 ETSs were operational in 55 jurisdictions while 18 jurisdictions collected a carbon tax. The papers in this special thematic section review the performance of many of these instruments over the 2005–2015 period. The performance of existing carbon taxes and GHG ETSs can help policy makers make informed choices about whether to introduce these instruments and to improve their design. The purpose of carbon pricing instruments is to reduce GHG emissions cost effectively. Assessing their performance is difficult because emissions are also affected by other policies and exogenous factors such as economic conditions. Carbon taxes in Europe prior to 2008 and in British Columbia reduced emissions from business-as-usual but actual emissions continued to rise. Since 2008 emissions subject to European carbon taxes have declined, but in most countries, other mitigation policies have probably contributed more to the reductions than the carbon taxes. Emissions subject to ETSs, with the exception of four systems without emissions caps, have declined. The ETSs contributed to the emissions reductions, but their share of the overall reduction is not known. Most tax rates are low relative to levels thought to be needed to achieve climate change objectives. Few jurisdictions regularly adjust their tax rates. All ETSs have accumulated surplus allowances and implemented measures to reduce these surpluses. The largest ETSs now specify annual reductions in their emissions cap several years into the future. Emissions trading system allowance prices are generally lower than the tax rates.

Key policy insights

• Theoretical discussions usually portray carbon taxes and GHG ETSs as alternatives. In practice, a jurisdiction often implements both instruments to address emissions by different sources.

• Designs of ETSs have evolved based on experience shared bilaterally and via dedicated institutions.

• Carbon tax designs, in contrast, have hardly evolved and there are no institutions dedicated to sharing experience.

• Every jurisdiction with an ETS and/or carbon tax also has other policies that affect its GHG emissions.

     

Achievability of the Paris Agreement targets in the EU: demand-side reduction potentials in a carbon budget perspective

Limiting global warming to ‘well below’ 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase even further to 1.5°C is an integral part of the 2015 Paris Agreement. To achieve these aims, cumulative global carbon emissions after 2016 should not exceed 940 – 390?Gt of CO₂ (for the 2°C target) and 167 – ?48?Gt of CO₂ (for the 1.5°C target) by the end of the century. This paper analyses the EU’s cumulative carbon emissions in different models and scenarios (global models, EU-focused models and national carbon mitigation scenarios). Due to the higher reductions in energy use and carbon intensity of the end-use sectors in the national scenarios, we identify an additional mitigation potential of 26–37 Gt cumulative CO₂ emissions up to 2050 compared to what is currently included in global or EU scenarios. These additional reductions could help to both reduce the need for carbon dioxide removals and bring cumulative emissions in global and EU scenarios in line with a fairness-based domestic EU budget for a 2°C target, while still remaining way above the budget for 1.5°C.

Key policy insights

• Models used for policy advice such as global integrated assessment models or EU models fail to consider certain mitigation potential available at the level of sectors.

• Global and EU models assume significant levels of CO₂ emission reductions from carbon capture and storage to reach the 1.5°C target but also to reach the 2°C target.

• Global and EU model scenarios are not compatible with a fair domestic EU share in the global carbon budget either for 2°C or for 1.5°C.

• Integrating additional sectoral mitigation potential from detailed national models can help bring down cumulative emissions in global and EU models to a level comparable to a fairness-based domestic EU share compatible with the 2°C target, but not the 1.5°C aspiration.

     

Ranking the risk of CO2 emissions from seagrass soil carbon stocks under global change threats

Seagrass meadows are natural carbon storage hotspots at risk from global change threats, and their loss can result in the remineralization of soil carbon stocks and CO₂ emissions fueling climate change. Here we used expert elicitation and empirical evidence to assess the risk of CO₂ emissions from seagrass soils caused by multiple human-induced, biological and climate change threats. Judgments from 41 experts were synthesized into a seagrass CO₂ emission risk score based on vulnerability factors (i.e., spatial scale, frequency, magnitude, resistance and recovery) to seagrass soil organic carbon stocks. Experts perceived that climate change threats (e.g., gradual ocean warming and increased storminess) have the highest risk for CO₂ emissions at global spatial scales, while direct threats (i.e., dredging and building of a marina or jetty) have the largest CO₂ emission risks at local spatial scales. A review of existing peer-reviewed literature showed a scarcity of studies assessing CO₂ emissions following seagrass disturbance, but the limited empirical evidence partly confirmed the opinion of experts. The literature review indicated that direct and long-term disturbances have the greatest negative impact on soil carbon stocks per unit area, highlighting that immediate management actions after disturbances to recover the seagrass canopy can significantly reduce soil CO₂ emissions. We conclude that further empirical evidence assessing global change threats on the seagrass carbon sink capacity is required to aid broader uptake of seagrass into blue carbon policy frameworks. The preliminary findings from this study can be used to estimate the potential risk of CO₂ emissions from seagrass habitats under threat and guide nature-based solutions for climate change mitigation.