Short introduction on Japan’s emissions

Although CO2 is the driving force behind the temperature changes, other gases such as methane (CH4) also contribute their share to global warming, for example through the exploitation of gas fields, and emissions by livestock. While methane is emitted much less than CO2 on a global scale, it is a much stronger greenhouse gas (GHG). Scientists estimated the relative strength of the important Kyoto greenhouse gases so that we can convert all emissions to an equivalent of CO2 emissions. For example, the emission of one ton of methane has approximately the warming effect of 25 tons of CO2. The factor of 25 reflects the climate forcing on a 100-year time horizon, following the Global Warming Potential presented in the IPCC Fourth Assessment Report (AR4).

With greenhouse gas emissions of approximately the equivalent of 1.3 giga tonnes of CO2 (Gt CO2eq), Japan contributed 2.71% to the global greenhouse gas emissions of 2017 (rank 6 - incl. EU27 on rank 3). All emissions estimates exclude emissions and absorption from land, which result from activities such as cutting down or planting of forests (Land Use, Land-Use Change and Forestry: LULUCF). Emissions from bunker fuels (international aviation and shipping) were also excluded, as they are not accounted for in national totals.

For 2030, Japan’s global contribution to greenhouse gas emissions is projected to decrease to approximately 2.18% (1.2 giga tonnes of CO2 equivalent / rank 8 - incl. EU27 on rank 4). The emissions projections for Japan were derived by downscaling the Shared Socio-Economic Pathways’ (SSPs) “Middle-of-the-Road” baseline marker scenario SSP2. These pathways describe certain narratives of socio-economic developments and were, i.a., used to derive greenhouse gas emissions scenarios that correspond to these developments. SSP2 is a narrative with little shifts in socio-economic patterns compared to historical ones, and is connected to medium socio-economic challenges for both climate mitigation and adaptation. While different models were used for each storyline, per SSP (SSPs1-5) one model was chosen as representative “marker scenario”. As the emissions projections are not readily available on country-level, but national estimates are important, the pathways were downscaled in the aftermath. In 2017, Japan represented 1.68% of the global population. Its Gross Domestic Product (GDP) in 2017 were 4.51% of the global GDP.

Looking at the highest contributing emissions sectors and gases separately, we find that in 2017 the highest contributing emissions sectors were Energy and IPPU (87.9% and 7.8%). Amongst the greenhouse gases that are considered in the Kyoto Protocol, the strongest contributor with 91.9% was CO2. This was followed by HFCs emissions, with a significantly lower share of 3.5%. When not considering the sectors and gases independently, but the sector-gas combinations instead, Energy CO2 and IPPU CO2 (87.3% and 3.7%) represented the largest emissions in 2017.

Greenhouse gas mitigation and Nationally Determined Contribution (NDC)

In 2015, the majority of countries agreed to the Paris Agreement (PA), with the goal of “Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change” (Article 2.1.a). Countries stated their pledges and targets towards achieving the PA’s goals in their Nationally Determined Contributions (NDCs). With Article 4.4 of the Paris Agreement, Parties decided that “Developed country Parties should continue taking the lead by undertaking economy-wide absolute emission reduction targets. Developing country Parties should continue enhancing their mitigation efforts, and are encouraged to move over time towards economy-wide emission reduction or limitation targets in the light of different national circumstances.”

In its 2020 NDC, Japan states that “post-2020 GHG emission reductions is at the level of a reduction of 26.0% by fiscal year (FY) 2030 compared to FY 2013 (25.4% reduction compared to FY 2005) (approximately 1.042 billion t-CO2 eq. as 2030 emissions)” (NDC, p. 4, the FY starts in April). Targets have not been changed from its 2015 submission. Japan’s target is unconditional on, e.g., international financial support or technology transfer. The country mentions that “Japan will, together with all major emitters, undertake domestic emission reductions and also contribute to reducing global greenhouse gas (GHG) emissions through Japan’s leading technologies and support for developing countries.” (NDC, p. 4).

The economy-wide target consists of a relative reduction against base year emissions. However, an estimate of the absolute target emissions is also given (1.042 Gg CO2eq AR4, NDC, p. 4). The availability of national estimates of emissions mitigation targets and pathways in line with countries’ NDCs is of great importance when, e.g., aggregating to global emissions to then derive, i.a., the resulting end-of-century warming levels. The target estimate includes a contribution by LULUCF, with “The target for removals is set as approximately 37 million t-CO2 (corresponding to 2.6% reduction of total emissions in FY 2013 (corresponding to 2.6% reduction of total emissions in FY 2005)) (approximately 27.8 million t-CO2 by forest carbon sinks measures (corresponding to 2.0% of total emissions in FY 2013 (corresponding to 2.0% reduction of total emissions in FY 2005)), and approximately 9.1 million t-CO2 by cropland management, grazing land management and revegetation (corresponding to 0.6% reduction of total emissions in FY 2013 (corresponding to 0.7% reduction of total emissions in FY 2005)).” (NDC, p. 10). Japan’s target covers all main IPCC sectors (Energy, IPPU, Agriculture, LULUCF, Waste), and all seven Kyoto GHGs (CO2, CH4, N2O, HFCs, PFCs, SF6, and NF3, which results in 100% of the nations emissions being targeted (sectors, gases, and 100% coverage stated on p. 6 of the NDC). While the given target emissions include LULUCF, additional quantitative information in the NDC (NDC, p. 8-10, 2030 targets (absolute target emissions and relative reductions), and 2005/2013 base year emissions for (non-)energy emissions and per gas, plus similar information on LULUCF) enables us to calculate the target excluding LULUCF as 1.079 Gg CO2eq.

Japan additionally mentions in its NDC that “As for the long-term, Japan submitted its Long-term Strategy under the Paris Agreement as Growth Strategy to the UNFCCC Secretariat in June 2019. In this strategy, Japan proclaims a”decarbonized society” and aims to accomplish it as early as possible in the second half of this century, based on the basic principle of “a virtuous cycle of environment and growth”. Japan will strive to achieve a “decarbonized society” as close as possible to 2050 with disruptive innovations, such as artificial photosynthesis and other CCUS technologies and realization of a hydrogen society.” (NDC, p. 1).

The NDC-assessment is based on Japan’s NDC submitted to the UNFCCC in March 2020.

The Figure below provides additional information, regarding both the baseline emissions used in our assessment and the quantified mitigated pathways for Japan.

Baseline emissions and mitigated emissions pathways based on the country’s Nationally Determined Contribution. In terms of national emissions, we look at the SSP2 baseline marker scenario, and the emissions of all IPCC sectors. Contributions from LULUCF are excluded (exclLU), and the emissions are based on GWPs from AR4. The left panel (a) shows the baseline emissions, indicating the contributions of the Kyoto Greenhouse Gases CO2, CH4, N2O, and the basket of F-gases to the national emissions. If we could extract baseline data exclLU from the NDC, you can see their values as black squares (converted from GWP SAR to AR4 if needed). In the right panel (b), the quantified mitigated emissions pathways are shown, based on information from the country’s NDC and also on non-NDC emissions baselines, per target conditionality and range (marked un-/conditional best/worst). Even though not all countries have targets with different conditionalities or ranges, we need assumptions for all four cases to build one global pathway per conditionality plus range combination and to derive corresponding temperature estimates. Therefore, we indicate these four pathways here. Per combination, we performed several quantifications with differing assumptions and show the median and the minimal and maximal pathways here. Additionally, if we could quantify the targets based on data extracted purely from the NDC - or if the targets were directly given in absolute emissions, these targets are shown as squares (in the GWP originally given in the NDC).


Data sources and further information

  • Historical emissions: PRIMAP-hist v2.1 (Guetschow et al., 2016, 2019).
  • Historical socio-economic data: PRIMAP-hist Socio-Eco v2.1 (Guetschow et al., 2019).
  • Projected emissions and socio-economic data: downscaled SSPs (Guetschow et al., 2020, 2020).
  • NDC quantifications: NDCmitiQ (Guenther et al., 2020, 2021).
  • GDP is given in purchasing power parity (PPP).
  • Main emissions sectors (Intergovernmental Panel on Climate Change, IPCC): Energy, Industrial Processes and Product Use (IPPU), Agriculture and LULUCF (Land Use, Land-Use Change and Forestry), also named AFOLU (Agriculture, Forestry and Other Land Use), and Waste.
  • Kyoto GHG: basket of several GHGs, namely carbon dioxide (CO2), Methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6), and since the second Kyoto Protocol period (2013-20) additionally nitrogen fluoride (NF3).
  • Global Warming Potentials (GWPs): GHGs have very different warming potentials. To make them comparable and for aggregation purposes, GWPs are used (how much energy will 1 ton of a certain gas absorb over a defined period of time, relative to the same mass of CO2?).


1 Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam, Germany