Incorporating blue carbon sequestration benefits into sub-national climate policies

The emissions reduction pledges made by individual countries through the 2015 Paris Agreement represent the current global commitment to mitigate greenhouse gas emissions in the face of the enduring climate crisis. Natural lands carbon sequestration and storage are critical for successful pathways to global decarbonization (i.e., as a negative emissions technology). Coastal vegetated habitats maintain carbon sequestration rates exceeding forest sequestration rates on a per unit area basis by nearly two orders of magnitude. These blue carbon habitats and their associated carbon sequestration benefits are vulnerable to losses from land-use change and sea-level rise. Incorporation of blue carbon habitats in climate change policy is one strategy for both maintaining these habitats and conserving significant carbon sequestration capabilities. Previous policy assessments have found the potential for incorporation of coastal carbon sequestration in national-level policies, yet there has – to date – been little inclusion of blue carbon in the national-scale implementation of Paris commitments. Recently, sub-national jurisdictions have gained attention as models for pathways to decarbonization. However, few previous studies have examined sub-national level policy opportunities for operationalizing blue carbon into climate decision-making. California is uniquely poised to integrate benefits from blue carbon into its coastal planning and management and its suite of climate mitigation policies. Here, we evaluated legal authorities and policy contexts addressing sequestration specifically from blue carbon habitats. We synthesized the progressive action in California’s approaches to mitigate carbon emissions including statutory, regulatory, and non-regulatory opportunities to incorporate blue carbon ecosystem service information into state- and local-level management decisions. To illustrate how actionable blue carbon information can be produced for use in decision-making, we conducted a spatial analysis of blue carbon sequestration in several locations in California across multiple agencies and management contexts. We found that the average market values of carbon sequestration services in 2100 ranged from $7,730 to $44,000 per hectare and that the social cost of carbon sequestration value was 1.3 to 2.7 times the market value. We also demonstrated that restoration of small areas with high sequestration rates can be comparable to the sequestration of existing marshes. Our results illustrate how accessible information about carbon sequestration in coastal habitats can be directly incorporated into existing policy frameworks at the sub-national scale. The incorporation of blue carbon sequestration benefits into sub-national climate policies can serve as a model for the development of future policy approaches for negative emissions technologies, with consequences for the success of the Paris Agreement and science-based decarbonization by mid-century.     

从科学和政策视角看碳预算对全球气候治理的作用

IPCC第五次评估报告进一步阐述和明确了全球平均地表温升与累积CO₂排放之间的近似线性关系。尽管在科学上仍存在一定的不确定性,国际社会对2℃温升目标及所对应的全球累积碳排放空间(即全球碳预算目标)已达成一定的科学认知和政治共识。但如何将碳预算从目标要求转变为各国决策和实际行动,仍是政策制定者们所面临的一个重要问题。在此背景下,提出建立一个有效的碳预算综合管理框架,努力避免人为温室气体排放导致气候系统危害,并利用其科学和政策的双重内涵,来推动谈判进程和加大行动力度,在新型气候治理模式下推动全球减排目标的实现。     

不同情景达到碳中和下中国区域气候变化的预估

利用第6次耦合模式比较计划(CMIP6)中的9个全球气候模式的模拟结果,通过CO₂浓度达峰时间确定SSP1-1.9和SSP1-2.6两种情景下的全球碳中和时间,预估了全球碳中和下中国区域气候较历史参考期(1995—2014年)的未来变化,分析不同时间达到碳中和下气候响应差异,并与未实现碳中和的SSP2-4.5情景下的气候变化对比。结果表明,SSP1-1.9和SSP1-2.6情景下全球达到碳中和的时间分别为2041年和2063年,相较于历史参考期,SSP1-1.9/SSP1-2.6下中国区域平均年气温上升1.22/1.58℃,平均年降水量增加7.1%/9.9%。SSP1-2.6(晚碳中和)较SSP1-1.9(早碳中和)情景下年均温增高约0.36℃,最大升温区位于西南及高原地区。对降水而言,晚碳中和较早碳中和全国平均年降水量增加约2.7%。全年及夏季降水量显著增加区主要在西北,新疆地区出现降水增加超过8%的大值区,冬季则集中于黄河中下游,增幅也超过8%。未碳中和的SSP2-4.5情景下中国区域的升温显著强于SSP1-2.6(碳中和)情景,年平均气温高约0.61℃,西北...     

Quantifying the social equity of carbon mitigation strategies

Many tools that are helpful for evaluating emissions mitigation measures, such as carbon abatement cost curves, focus exclusively on cost and emissions reduction potential without quantifying the direct and indirect impacts on stakeholders. The impacts of climate change will be the most severe and immediate for billions of poor people, especially for those whose livelihoods are based on agriculture and subsistence activities and are directly dependent on weather patterns. Thus, equity and vulnerability considerations must be central to GHG emissions reduction strategies. A case study of a carbon abatement cost curve for an electricity system in two Nicaraguan rural villages is presented and is complemented with assessments based on the poverty metrics of the poverty headcount, the Gini coefficient, and the Kuznets ratios. Although these metrics are relatively easy to calculate, the study provides a general indication as to how the social impacts of mitigation strategies on the poor (whether they are in rural or urban environments, developed or developing countries) can be revealed and highlights the inequalities that are embedded in them. Further work analysing how mitigation measures affect the various more detailed poverty indices, such as the Human Development, Gender Equality, or Multidimensional Poverty indices, is needed.     

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.

     

Implications of different climate protection regimes for the EU-27 and its member states through 2050

It is a broadly accepted fact that a clear reduction of global GHG emissions is required to limit the increase of global warming to a tolerable level. A key issue in this context is the optimal breakdown of reduction targets among different world regions or even countries. Using the European Commission-funded PLANETS project, cost-optimal global burden sharing to reach global GHG reduction targets was analysed, and an optimal allocation of GHG reductions was identified, relative to the global target, to the commitments of different world regions and the trade possibilities for emission certificates. Specifically, it is evaluated how Europe can contribute in a cost-optimal way to keeping the global concentration of GHGs in the atmosphere below 530 parts per million equivalent (ppme) or below a stricter global reduction target of 500 ppme. Based on the energy system model TIMES PanEU, the potentials for emissions reduction in the different energy sectors and EU Member States and the role of key technologies are analysed. The most cost-effective potentials for GHG reductions in Europe are in the conversion/production, residential and industrial sectors. Substantial reductions in the transport sector occur only under very stringent reduction targets. Achieving ambitious reduction targets requires considerable contributions from all EU Member States until 2050.     

Funding low-carbon investments in the absence of a carbon tax

Introducing a carbon tax is difficult, partly because it suggests that current generations have to make sacrifices for the benefit of future generations. However, the climate change externality could be corrected without such a sacrifice. It is possible to set a carbon value, and use it to create ‘carbon certificates’ that can be accepted as part of commercial banks’ legal reserves. These certificates can be distributed to low-carbon projects, and be exchanged by investors against concessional loans, reducing capital costs for low-carbon projects. As the issuance of carbon certificates would increase the quantity of money, it will either lead to accelerated inflation or induce the Central Bank to raise interest rates. Low-carbon projects will thus have access to cheaper loans at the expense of either ‘regular’ investors (in case of higher interest rates) or of lenders and depositors (in case of accelerated inflation). Within this scheme, mitigation expenditures are compensated by a reduction in regular investments, so that immediate consumption is maintained. It uses future generation wealth to pay for a hedge against climate change. This framework is not as efficient as a carbon tax but is politically easier to implement and represents an interesting step in the trajectory towards a low-carbon economy.     

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.     

Dependence of wheat and rice respiration on tissue nitrogen and the corresponding net carbon fixation efficiency under different rates of nitrogen application

To quantitatively address the role of tissue N in crop respiration under various agricultural practices, and to consequently evaluate the impact of synthetic fertilizer N application on biomass production and respiration, and hence net carbon fixation efficiency （Encf）, pot and field experiments were carried out for an annual rotation of a rice-wheat cropping system from 2001 to 2003. The treatments of the pot experiments included fertilizer N application, sowing date and planting density. Different rates of N application were tested in the field experiments. Static opaque chambers were used for sampling the gas. The respiration as CO2 emission was detected by a gas chromatograph. A successive biomass clipping method was employed to determine the crop autotrophic respiration coefficient （Ra）. Results from the pot experiments revealed a linear relationship between Ra and tissue N content as Ra = 4.74N-1.45 （R^2= 0.85, P 〈 0.001）. Measurements and calculations from the field experiments indicated that fertilizer N application promoted not only biomass production but also increased the respiration of crops. A further investigation showed that the increase of carbon loss in terms of respiration owing to fertilizer N application exceeded that of net carbon gain in terms of aboveground biomass when fertilizer N was applied over a certain rate. Consequently, the Encf declined as the N application rate increased.