4. The rapidly closing window to prevent dangerous climate change

According to the UN’s Intergovernmental Panel on Climate Change (IPCC), any further delay in reducing greenhouse gas emissions will miss a brief and rapidly closing window of opportunity to secure a liveable future for all.¹⁴IPCC, AR6 Synthesis Report: Summary for Policymakers, 2023, para. C.1.

Already at the current level of 1.2°C of global warming, climate change has caused widespread adverse impacts to nature and people, which are projected to increase exponentially if global warming exceeds the critical 1.5°C threshold. The remaining amount of CO₂ that can be emitted to remain within 1.5°C (the remaining carbon budget) is set to be exhausted between 2025-2030. Exceeding 1.5°C also risks triggering tipping points and feedback loops, which may greatly accelerate global warming and lead to abrupt and irreversible changes in the Earth’s climate system.¹⁵IPCC, AR6 WGI The Physical Science Basis, 2021, p. 21; IPCC, Special Report on Global Warming of 1.5°C, 2018, pp. 262-264; IPCC, AR6 WGI The Physical Science Basis: Summary for Policymakers, 2021, para. C.3.2 and table SPM.1 at p.18; David Armstrong McKay et al., “Exceeding 1.5°C global warming could trigger multiple climate tipping points” Science 377, nr. 6611 (2022); Will Steffen et al., “Trajectories of the Earth System in the Anthropocene” PNAS 115, no. 33 (2018); Nico Wunderling, et al., “Global warming overshoots increase risks of climate tipping cascades in a network model.” Nature Climate Change 13 (2023).

In Article 2.1a of the Paris Agreement, State Parties agree to “pursue efforts to limit” the global temperature increase to 1.5°C above pre-industrial levels, with a maximum increase to “well below 2°C”. New insights in the IPCC’s 2018 report, confirmed in 2021 and 2022, have shifted the scientific, political and legal consensus towards limiting the temperature increase to 1.5°C instead of 2°C, as this would “substantially reduce” the risks for humans.¹⁶IPCC, Special Report on Global Warming of 1.5°C, 2018, pp. 177–181; IPCC, AR6 WGI The Physical Science Basis: Summary for Policymakers, 2021, pp. 19–24; IPCC. Climate Change 2022: Impacts, Adaptation and Vulnerability: Summary for Policymakers para. B.3.

Hence, at the last three UN climate conferences, the State Parties to the Paris Agreement have resolved “to pursue efforts to limit the temperature increase to 1.5°C”.¹⁷UNFCCC Conference of the Parties, Glasgow Climate Pact, 08.03.22, UN Doc. FCCC/PA/CMA/2021/10/Add.1, paras. 20–22; UNFCCC Conference of the Parties, Sharm el-Sheikh Implementation Plan, 20.11.2022, UN Doc. FCCC/PA/CMA/2022/L.21, para 28; UNFCCC Conference of the Parties, Outcome of the First Global Stocktake, 13.12.2023, UN Doc. FCCC/PA/CMA/2023/L.17, para. 4. At the most recent climate conference in Dubai, State Parties also recognised the need for “deep, rapid and sustained reductions in GHG emissions in line with 1.5 °C pathways” and agreed to “transition away from fossil fuels in energy systems, in a just, orderly and equitable manner, accelerating action in this critical decade, so as to achieve net zero by 2050 in keeping with the science”.¹⁸Ibid, para. 28(d). In Europe, the EU Climate Act states that climate change is an “existential threat” and that global temperature increase must be “limited to 1.5°C”.¹⁹Regulation (EU) 2021/1119 (European Climate Law) preamble rec. 1 and 3.

According to the IPCC, limiting warming to 1.5°C requires a 48% global reduction in CO₂ emissions from 2019 levels by 2030 and net zero emissions by 2050.²⁰IPCC, AR6 WGIII Mitigation of Climate Change: Summary for Policymakers, 2022, paras. C.2 and C.1.2. However, as States have “common but differentiated responsibilities and respective capabilities”, developed countries must cut at a higher rate.²¹UNFCCC, Art 3.1, Art 4.1; Paris Agreement, Preamble, Art 2.1, 4.1, 4.2, 4.3 and 4.4. While opinions on how to assess a country’s fair share of the remaining carbon budget differs, one study from legal scholars and climate scientists suggests that, when adjusting for historic responsibility for climate change and GDP per capita, developed States should reach net zero emissions by 2030 in order to stay within their fair share of the remaining 1.5°C global carbon budget.²²Lavanya Rajamani et al., “National ‘fair shares’ in reducing greenhouse gas emissions within the principled framework of international environmental law” Climate Policy 21, no. 8 (2021) p. 17.

In 2023, the remaining global carbon budget for limiting warming to 1.5°C was approximately 150 billion tonnes of carbon dioxide, which will be exhausted within 2025-2030 under the current rate of global emissions.²³Piers M. Forster et al., “Indicators of Global Climate Change 2022” Earth System Science Data 15, no. 6 (2023) ch. 8; Zhu Liu et al., “Monitoring global carbon emissions in 2022” Nature Reviews Earth & Environment 4 (2023). An earlier estimate put the remaining carbon budget in 2020 at 400 GtCO₂, see IPCC, AR6 WGI The Physical Science Basis: Summary for Policymakers, 2021, p. 29. New evidence and additional observational data indicate that the remaining carbon budget is now much lower. These carbon budgets are based on a 67% probability of limiting global warming to 1.5°C.

As of November 2023, States’ current policies to reduce emissions will still lead to a 3°C temperature rise by 2100 (see Figure 1 below).²⁴Matthew Jones et al., “National contributions to climate change due to historical emissions” Scientific Data 10, no. 1 (2023); UNEP, Emissions Gap Report: The Closing Window (2022), p. 35, figure 4.3; UNFCCC Subsidiary Body for Scientific and Technological Advice, Technical Dialogue of the First Global Stocktake, 8.09.2023, UN Doc. FCCC/SB/2023/9, p. 17, figure 1; CarbonBrief, “UNEP: Meeting global climate goals now requires rapid transformation of societies”, 27.10.2022; UNEP, Emissions Gap Report: Broken Record (2023), p. 31, table 4.4. Implementation of States’ emission reduction targets which are achievable using domestic resources, known as unconditional NDCs, will only reduce this to 2.9°C. Implementation of States’ targets which are dependent on external financial support, known as conditional NDCs, will reduce warming to 2.5°C.²⁵UN Environment Program (UNEP), Emissions Gap Report: Broken Record (2023), p. XXII and 30-31.

Only an urgent system-wide transformation can deliver the enormous emission cuts needed to limit warming to 1.5°C and avoid climate disaster. This requires actions and changes across all sectors and systems, including in energy, industry, transport, buildings, agriculture, forestry and the food and financial systems, while also ensuring a just transition.²⁶United Nations Environment Programme, Emissions Gap Report 2023: Broken Record – Temperatures hit new highs, yet world fails to cut emissions (again), 2023.

The energy sector is the most critical as it accounts for two-thirds of global GHG emissions.²⁷International Energy Agency (IEA), “Energy sector is central to efforts to combat climate change”, 2023, https://www.iea.org/topics/climate-change. Over 80% of all CO₂ emissions since 1751 have come from the burning of fossil fuels and more than half have been emitted in the last 33 years.²⁸IPCC, AR6 Climate Change 2021 The Physical Science Basis, 2021, pp. 676, 687, 688; Stainforth et al., “More than half of all CO2 emissions since 1751 emitted in the last 30 years”, Institute for European Environmental Policy, 29.04.2020.

Estimated future emissions from existing fossil fuel infrastructure already exhaust the remaining 1.5°C global carbon budget, and the additional emissions from planned fossil fuel infrastructure exhaust even the 2°C budget.²⁹IPCC, AR6 WGIII Mitigation of Climate Change, 2022, Technical Summary p. 26 and Chapter 2 p. 72. According to a “large consensus” across multiple climate models, “developing any new oil and gas fields is incompatible with limiting warming to 1.5°C”.³⁰Conclusion of a meta-study from the International Institute for Sustainable Development (IISD), Navigating Energy Transitions: Mapping the road to 1.5°C, 21.10.2022 p. 14 ff., referring inter alia to reports from the IPCC and IEA, World Energy Outlook, 2021, p. 112; IEA, Net Zero by 2050, 2021, pp. 23, 99. Furthermore, the world must cut an additional 23 gigatonnes of CO₂ emissions and add 1020 gigawatts of solar and wind power every year until 2030 to remain within a 1.5°C pathway.³¹Ibid; IEA, Net Zero by 2050: A Roadmap for the Global Energy Sector: Summary for Policymakers, 2021, p.3. According to the modelling used by the International Energy Agency, renewable energy investment will need to triple by 2030 and wind and solar will need to increase from 10% of total electricity generation to 40% to remain within a 1.5°C pathway.³²IEA, World Energy Investment, 2023, p. 57; IEA, World Energy Outlook, 2022, pp. 97, 138 and 257.

Increases in renewable energy production must be accompanied by decreases in fossil fuel production. The Norwegian Environment Agency points out that, “increased production of renewable energy does not in itself result in reduced emissions, since climate gains are only achieved when the new energy replaces the use of fossil energy”.³³Norwegian Environment Agency, Veileder: Produksjon og distribusjon av fornybar energi, 15.09.2023, https://www.miljodirektoratet.no/ansvarsomrader/klima/for-myndigheter/kutte-utslipp-av-klimagasser/klima-og-energitiltak/fornybar-energi/produksjon-og-distribusjon-av-fornybar-energi/. While renewable energy production is increasing globally, so is fossil fuel production, despite the UN warning that governments plan to produce more than double the amount of fossil fuels than what is consistent with a 1.5°C pathway.³⁴UNEP et al. The Production Gap: Phasing down or phasing up? Top fossil fuel producers plan even more extraction despite climate promises, 2023. Between 2017 and 2022, renewable energy production met only half of the new demand for energy globally, and is far from replacing fossil fuels in absolute terms.³⁵DNV, Energy Transition Outlook 2023, 11 October 2023.