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Aug.  2022

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# Climate Warming Mitigation from Nationally Determined Contributions

• Individual countries are requested to submit nationally determined contributions (NDCs) to alleviate global warming in the Paris Agreement. However, the global climate effects and regional contributions are not explicitly considered in the countries’ decision-making process. In this study, we evaluate the global temperature slowdown of the NDC scenario (∆T = 0.6°C) and attribute the global temperature slowdown to certain regions of the world with a compact earth system model. Considering reductions in CO2, CH4, N2O, BC, and SO2, the R5OECD (the Organization for Economic Co-operation and Development in 1990) and R5ASIA (Asian countries) are the top two contributors to global warming mitigation, accounting for 39.3% and 36.8%, respectively. R5LAM (Latin America and the Caribbean) and R5MAF (the Middle East and Africa) followed behind, with contributions of 11.5% and 8.9%, respectively. The remaining 3.5% is attributed to R5REF (the Reforming Economies). Carbon Dioxide emission reduction is the decisive factor of regional contributions, but not the only one. Other greenhouse gases are also important, especially for R5MAF. The contribution of short-lived aerosols is small but significant, notably SO2 reduction in R5ASIA. We argue that additional species beyond CO2 need to be considered, including short-lived pollutants, when planning a route to mitigate climate change. It needs to be emphasized that there is still a gap to achieve the Paris Agreement 2-degree target with current NDC efforts, let alone the ambitious 1.5-degree target. All countries need to pursue stricter reduction policies for a more sustainable world.
摘要: 《巴黎协定》规定了各个国家应提交国家自主贡献以缓解全球变暖。然而，各国在制定国家自主贡献时，并未明确考虑全球气候影响和区域减排贡献，因此有必要评估各国的国家自主贡献对减缓气候变化的贡献。本文首先模拟了自出减排情景下相对于无政策情景升温减缓了0.6℃，并通过简化地球系统模型将全球升温减缓归因于全球不同区域的减排行动。在考虑二氧化碳、甲烷、氧化亚氮、黑碳和二氧化硫五种气候强迫物质的减排情况下，经合组织成员国和亚洲国家是减缓全球变暖的两大贡献者，分别贡献了39.3% 和36.8%。拉美国家、中东非国家和转型经济体国家分别贡献了剩下的11.5%、8.9%和3.5%。二氧化碳的减排是区域贡献的决定性因素，但不是唯一因素。其他温室气体也很重要，尤其是对于中东非国家。气溶胶的贡献很小但是显著，特别是亚洲国家中的对二氧化硫的减排。我们认为，在规划减缓气候变化的路线时，需要考虑二氧化碳以外的其他物质，包括短期污染物。需要强调的是，目前的减排政策距离实现《巴黎协定》2℃目标仍有差距，更不必说雄心勃勃的1.5℃目标了。所有国家都需要采取更严格的减排政策，以实现世界的更可持续发展
• Figure 1.  CO2 emissions of the R5 regions based on the CD-LINKS scenario dataset. Future CO2 emissions in the R5 region under four climate scenarios. The line is the average of the results of the five emission IAMs, and the shaded areas show the range of the scenario data. “NP”, “NDC”, and “2-degree” scenarios are marked by red, orange, and solid blue lines. The “1.5-degree” scenario is marked by green dashed lines. Pathways of other species (CH4, N2O, BC, and SO2) can be found in Fig. S1.

Figure 2.  CH4, N2O, BC, and SO2 emissions of the R5regions based on the CD-LINKS scenario dataset. Future CH4, N2O, BC, and SO2 emissions in the R5 region in four climate scenarios. The line is the average of the results of the five emission IAM and the shade shows the range of the scenario data. “NP”, “NDC”, and “2-degree” scenarios are marked by red, orange, and blue solid lines. “1.5-degree” scenario is marked by green dashed lines.

Figure 3.  The mitigation of CO2, CH4, N2O, BC, and SO2 emissions of the R5 regions based on the CD-LINKS scenario dataset. The map shows the regionalization (R5 regions) in this study. The bars around the map show emission reductions of NDC relative to NP scenarios. The cumulative reduction (for CO2, CH4, and N2O) or annual reductions (for BC and SO2) are shown here. The height of each column is a global emission difference, with the different colors representing the various R5 regions. The results are based on five IAMs are marked by different markers, and their average is shown with grey bars. The units are 100 PgC for CO2, 10 TgN for N2O, 1000 TgC for CH4, 0.01 TgC for BC, and 1 TgS for SO2 to plot the bars in one axis.

Figure 4.  Atmospheric CO2 increase ($\Delta {\mathrm{C}\mathrm{O}}_{2}$) and temperature change ($\Delta T$) relative to preindustrial (1850) simulations for scenarios. (a) The simulation of $\Delta {\mathrm{C}\mathrm{O}}_{2}$ based on emission data from the five IAMs. The mitigation of $\Delta {\mathrm{C}\mathrm{O}}_{2}$ induced by NDC relative to NP is marked and valued in the figures. $\Delta {\mathrm{C}\mathrm{O}}_{2}$ in the 2-degree and 1.5-degree scenarios are also shown in the figures for comparison. (b) The same as (a), but for $\Delta T$. The mitigation of temperature increases is the core concern of this study and is attributed to regions in this study.

Figure 5.  The transient climate response to cumulative carbon emissions (TCRE) in this study. The lines are the average of the results of 3000 simulations and the shades show the range of the simulated data. “NP”, “NDC”, “2-degree” and “1.5-degree” scenarios are marked by red, orange, blue and green dashed lines. We calculate the TCRE for NDC scenario and NP scenario as the slope. Considering the negative emissions of the 2-degree and 1.5-degree scenarios, we do not calculate the TCRE for these two scenarios.

Figure 6.  The relative contributions of regions to climate mitigations with different climate forcers included. Each column represents the global climate mitigations (100%), with relative contributions from the R5 regions marked by different colors. “CO2”, “GHGs”, “GHGs + SO2”, “GHGs + BC”, and “all” labeled at the axis indicate which climate forcings are considered. GHGs refer to CO2, CH4, and N2O, and “all” refers to GHGs, BC, and SO2. The close-together columns represent results based on different IAMs, with the model average indicated by the red dashed lines. The five IAMs are AIM/CGE 2.1, IMAGE 3.0.1, MESSAGEix-GLOBIOM 1.0, REMIND-MAgPIE 1.7-3.0, and WITCH-GLOBIOM 4.0 (from left to right).

Figure 7.  Pie charts for regional emission reductions and induced climate warming mitigations. (a) Pie charts for regional reductions in CO2, CH4, N2O, BC, and SO2. (b) The nested pie chart in the center of this figure shows the regional relative contributions when calculated with different amounts of substances considered. The center part of the nested pie chart shows the relative contributions calculated with only CO2 considered. The second layer, from the inside to the outside, considers CH4 and N2O in addition to CO2 (abbreviated as GHGs in this study). The third layer considers GHGs and BC, and the fourth layer considers GHGs and SO2. The outermost layer considers GHGs, BC, and SO2, referred to as “all” in this study.

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## Manuscript History

Manuscript revised: 29 March 2022
Manuscript accepted: 30 March 2022
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Climate Warming Mitigation from Nationally Determined Contributions

###### Corresponding author: Bengang LI, libengang@pku.edu.cn
• 1. Sino-French Institute for Earth System Science, MOE Key Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
• 2. International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria
• 3. Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ, 91191 Gif-sur-Yvette, France

Abstract: Individual countries are requested to submit nationally determined contributions (NDCs) to alleviate global warming in the Paris Agreement. However, the global climate effects and regional contributions are not explicitly considered in the countries’ decision-making process. In this study, we evaluate the global temperature slowdown of the NDC scenario (∆T = 0.6°C) and attribute the global temperature slowdown to certain regions of the world with a compact earth system model. Considering reductions in CO2, CH4, N2O, BC, and SO2, the R5OECD (the Organization for Economic Co-operation and Development in 1990) and R5ASIA (Asian countries) are the top two contributors to global warming mitigation, accounting for 39.3% and 36.8%, respectively. R5LAM (Latin America and the Caribbean) and R5MAF (the Middle East and Africa) followed behind, with contributions of 11.5% and 8.9%, respectively. The remaining 3.5% is attributed to R5REF (the Reforming Economies). Carbon Dioxide emission reduction is the decisive factor of regional contributions, but not the only one. Other greenhouse gases are also important, especially for R5MAF. The contribution of short-lived aerosols is small but significant, notably SO2 reduction in R5ASIA. We argue that additional species beyond CO2 need to be considered, including short-lived pollutants, when planning a route to mitigate climate change. It needs to be emphasized that there is still a gap to achieve the Paris Agreement 2-degree target with current NDC efforts, let alone the ambitious 1.5-degree target. All countries need to pursue stricter reduction policies for a more sustainable world.

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