The Paris Agreement and NDCs: are the national mitigation targets sufficient to stay below the 1.5-2°C limit?

Short introduction on the UK’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 481.9 mega tonnes of CO₂ (Mt CO₂eq), the UK contributed 1.011% to the global greenhouse gas emissions of 2017 (rank 18 - 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, the UK’s global contribution to greenhouse gas emissions is projected to stay at a similar level of approximately 0.98% (550.3 mega tonnes of CO₂ equivalent / rank 18 - incl. EU27 on rank 4). The emissions projections for the UK 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, the UK represented 0.88% of the global population. Its Gross Domestic Product (GDP) in 2017 were 2.46% 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 Agriculture (79.5% and 8.6%). Amongst the greenhouse gases that are considered in the Kyoto Protocol, the strongest contributor with 81.9% was CO₂. This was followed by CH₄ emissions, with a significantly lower share of 10.8%. When not considering the sectors and gases independently, but the sector-gas combinations instead, Energy CO₂ and Agriculture CH₄ (77.5% and 5.4%) 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 NDC, the United Kingdom communicates as mitigation target “An economy-wide net reduction in GHG emissions of at least 68% by 2030 compared to reference year levels.” (NDC, p. 5). The base years differ per gas, and base year emissions used for the target calculations are not fixed yet, as “The reference indicator (MtCO₂e) in the reference years (1990 [for CO₂, CH₄, and N₂O] and 1995 [for F-gases]) will be based on the 1990-2030 UK GHG Inventory submitted to the UNFCCC in 2032. The value for the target year (2030) will be based on applying a 68% fixed percentage reduction target to the reference indicator value.” (NDC, p. 4). Even though not stated explicitly, we expect the UK’s contribution to be unconditionally on, e.g., international support. For Scotland, specific target information is provided, stating that “This sets in law Scotland’s target to reach net zero GHG emissions by 2045, and interim targets of 56%, 75% and 90% reductions in emissions by 2020, 2030 and 2040 respectively, relative to a 1990/1995 baseline. Scotland sets annual targets, in contrast to the five-yearly carbon budgets set by the UK and Welsh Governments.” (NDC, p. 9-10).

Previously, the UK used to be part of the EU and its NDC. Now, for the first time, it submitted a separate NDC, indicating that “The UK’s NDC represents a step forward for the UK’s ambition to tackle climate change over the next ten years, as the UK accelerates towards meeting the legally binding commitment to net zero by 2050. It is a significant increase from the UK’s previous contribution to the EU’s Intended NDC of 40% by 2030, which was estimated to be a 53% UK reduction on reference levels.” (NDC, p. 29). The submitted NDC does not include a quantified target or the emissions data necessary to calculate the absolute target emissions from the given relative reduction of at least 68% by 2030 compared to the respective reference year levels. Therefore, a quantification of the UK’s contribution depends on “external” (non-NDC) emissions data. 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. Included in the NDC is an estimate in terms of expected mitigated per capita emissions, however. “By reducing emissions by at least 68% on reference year levels (1990/1995), UK emissions per person will fall from around 14 tCO₂e in 1990 to fewer than 4 tCO₂e in 2030.” (NDC, p. 30).

The UK’s declares “An economy-wide net reduction” (NDC, p. 5), mentioning all main IPCC sectors explicitly as covered (“Energy (including transport); Industrial Processes and Product Use (IPPU); Agriculture; Land-use, Land-Use Change and Forestry (LULUCF); and Waste.”, NDC, p. 6), as well as all seven Kyoto GHGs (NDC, p. 6). Also, the reference indicator are “Net greenhouse gas (GHG) emissions” (NDC, p. 4). This results in the UK’s entire national emissions and removals being included in its NDC. It chose two different base years, depending on the respective GHG (1990: CO₂, CH₄, and N₂O; 1995: HFCs, PFCs, SF₆, and NF₃; NDC, p. 5). Additional information on LULUCF and the planned accounting and covered pools are available in the NDC (NDC, p. 6+27). Furthermore, the UK provides information on its decision not to include emissions from International Aviation and Shipping, being “supportive [however] of efforts to reduce these emissions through action under the International Civil Aviation Organisation and the International Maritime Organisation.” (NDC, p. 7-8).

Regarding the geographical scope of this NDC, it is declared that “In the UK GHG Inventory submission to the UNFCCC, the UK will continue to report emissions on behalf of the Crown Dependencies (Jersey, Guernsey, Isle of Man) and the Overseas Territories (Bermuda, Cayman Islands, Falkland Islands, Gibraltar) which have joined the UK’s instrument of ratification of the Convention. These emissions currently constitute approximately 1% of the UK emissions total.” (NDC, p. 7).

Concerning Article 6 of the PA (cooperation and markets), the NDC indicates that “While the UK intends to meet its NDC target through reducing emissions domestically, it reserves the right to use voluntary cooperation under Article 6 of the Paris Agreement. Such use could occur through the linking of a potential UK emissions trading system to another emissions trading system or through the use of emissions reductions or removals units.” (NDC, p. 29).

As for its long-term vision, the UK mentions that “Ahead of COP26, the UK intends to publish a comprehensive Net Zero Strategy, setting out the government’s vision for transitioning to a net zero economy by 2050, making the most of new growth and employment opportunities across the UK.” (NDC, p. 11).

The NDC-assessment is based on the UK’s NDC submitted to the UNFCCC in December 2020. Relying on “external” non-NDC data (SSP2) and the assessed national share of targeted emissions, for the UK we quantify the 2030 unconditional target as 260.1 Mt CO₂eq AR4 (relative reduction against base year emissions: -68%, inclLU).

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

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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).

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FIG 1

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?).