Scenarios for mitigating CO₂ emissions from energy supply in the absence of CO₂ removal

ABSTRACT

This paper investigates the effectiveness of different energy scenarios for achieving early reductions in global energy-related CO₂ emissions on trajectories to zero or near-zero emissions by 2050. To keep global heating below 1.5°C without overshoot by 2050, global CO₂ emissions must decline by about half by 2030. To achieve rapid, early emission reductions entails substantially changing recent pre-COVID (2000–2019) observed trends, which comprise increasing total primary energy supply (TPES) and approximately constant fraction of TPES derived from fossil fuels (FF fraction). Scenarios are developed to explore the effects of varying future trends in these variables in the absence of substantial CO₂ removal, because relying on the latter is speculative and risky. The principal result is that, to reduce energy-related emissions to at least half the 2019 level by 2030 en route to zero or near-zero CO₂ emissions by 2050, either TPES must be reduced to at least half its 2019 value by 2050 or impossibly rapid reductions must be made in the FF fraction of supply, given current technological options. Reduction in energy consumption likely entails economic degrowth in high-income countries, driven by policies that are socioeconomic, cultural and political, in addition to technological. This needs serious consideration and international cooperation.

Key policy insights

• If global energy consumption grows at the pre-COVID rate, technological change alone cannot halve global CO₂ emissions by 2030 and hence cannot keep global heating below 1.5°C by 2050.

• In the absence of substantial CO₂ removal, policies are needed to reduce global energy consumption and hence foster degrowth in high-income economies.

• Policies to drive technological and socioeconomic changes could together cut global energy consumption and thus total primary energy supply and associated emissions by at least 75% by 2050.

KEYWORDS:

• climate mitigation scenarios
• renewable energy
• energy efficiency
• total primary energy supply
• fossil fuel fraction
• degrowth
• steady-state economy

Acknowledgments

The author thanks the reviewers and editor for valuable comments that led to substantial improvements in the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 This is a large-scale simulation model designed to replicate how energy markets function and generates detailed sector-by-sector and region-by region energy projections.

2 However, there is debate about the possible timescale and whether there are significant roles for certain technologies, namely bioenergy, nuclear energy or large-scale CO₂ removal.

3 A consumption-based approach is also possible but not pursued here, because greenhouse gases from electricity supply are emitted from the combustion of primary energy.

4 We focus on non-combustible RE (e.g. wind, solar and hydro-electricity), because biofuels are unlikely to make a large contribution in the future on account of environmental concerns.

5 Reducing CO₂ emissions to zero or near zero will automatically reduce CO₂e to near-zero, because fugitive (methane) emissions will be greatly reduced.

6 Half-life is the time required for the decaying quantity to fall to half its initial value.

7 X represents such processes as electrolysis of water to produce hydrogen for many purposes including the manufacture of steel, fertilisers and chemicals; water pumping; and seawater desalination.

8 Government-issued currency that is not backed by a physical commodity such as gold, but rather by the government that issued it. States that are sovereign in currency include the USA, UK, Japan, China and Australia, but not individual members of the European Union.

9 Relevant types of storage technologies include grid-integrated batteries, pumped hydro, and compressed air. Financing policies are needed because, where banks and other financial institutions may hesitate to lend, a government-funded lender, such as Australia’s Clean Energy Finance Corporation (CEFC, n.d.) can stimulate investment.

10 In addition to the ethical case for social justice, this policy has potential economic benefits and would assist in gaining worker and community support for the more radical climate and energy policies (see Section 4.3) to reduce energy demand substantially and, beyond that, to cut all GHG emissions.

11 At present, construction of RE and EE technologies requires some use of FF. Already RE is beginning to be used for mining and processing the raw materials and for the electricity used in manufacture, so that over time RE and EE technologies will be made increasingly with RE inputs (Diesendorf, 2022, section 3.6).

12 For example those that are net generators of electricity such as hydro-electricity (not pumped) and concentrated solar thermal power with thermal storage. (Diesendorf & Wiedmann, 2020)

Additional information

Funding

No funding was received for this research.