Global Methane Assessment

Generated Summary

This document presents an assessment of methane emissions mitigation, focusing on the opportunities, impacts, and uncertainties associated with various strategies. The study employs a multi-model approach, utilizing five state-of-the-art global composition-climate models to evaluate changes in the Earth’s climate system and surface ozone concentrations in response to methane emission reductions. The research explores the potential for reducing warming and the impacts associated with ozone formation by decreasing methane emissions. The core methodology involves analyzing the effects of different methane mitigation strategies across various sectors, including fossil fuels, waste, and agriculture. The study compares these scenarios with those consistent with keeping global mean temperatures below the 1.5°C target, as defined by the Intergovernmental Panel on Climate Change (IPCC). The analysis evaluates both the potential for abatement and the associated costs by sector and explores the impact on human health, crop yields, and labour productivity. Furthermore, the study examines the effectiveness of methane-specific policies and the role of behavioural changes in mitigating methane emissions. The assessment also investigates the influence of various factors, such as income elasticity and discounting rates, on the valuation of impacts. The findings of the research provide insights into the most effective strategies for reducing methane emissions, highlighting the importance of both targeted controls and additional measures to achieve climate and environmental goals.

Key Findings & Statistics

• Implementation of targeted control measures with costs less than the estimated societal benefits could abate approximately 100 Mt/yr of methane emissions by 2030.
• These measures could provide benefits including reducing global warming by approximately 0.15°C over the 2040-2070 period, and by approximately 0.2°C over the longer term (2070-2100).
• Targeted controls could prevent premature deaths due to ozone exposure immediately with annual totals reaching approximately 140 000 per year in 2030.
• Targeted controls could prevent approximately 40 billion lost work hours annually due to heat exposure annually by about 2045.
• Targeted controls could prevent approximately 15 Mt tonnes of crop losses due primarily to ozone exposure each year by 2030.
• The crop yield increases would be worth approximately US$ 4 billion per year.
• The increased labour productivity would be worth approximately US$ 6.3 billion per year.
• The valuation of the reduced risk of premature deaths is approximately US$ 250 billion (US$60-420; 95 per cent confidence interval).
• The greatest targeted abatement potential very likely lies within the fossil-fuel sector.
• Average mitigation costs for fossil-fuel sector range from a high of approximately US$1 250 per tonne of methane in the US EPA analysis to a net savings of approximately US$ 400 per tonne in the IIASA analysis.
• The low-cost measures that are below US$ 600 per tonne, have an abatement potential of approximately 75 ±2 Mt/yr.
• Benefits from this level of abatement include approximately 0.13°C warming avoided in the 2040–2070 period, ~105 000 avoided premature deaths due to ozone exposure annually by 2030, and 11 Mt of avoided crop losses due primarily to ozone exposure each year.
• The benefits of the annually avoided premature deaths alone are estimated at US$ 190 billion (US$ 40–310 billion; 95 per cent confidence interval).
• Targeted measures alone are not enough to reach emissions levels seen in 1.5°C scenarios over the next several decades.
• These scenarios require both targeted and additional measures to achieve approximately 180 Mt/yr of methane abatement by 2030.
• Behavioural measures include fuel switching, energy efficiency, improved waste separation, reducing food waste, dietary change and transport demand management.
• The total worldwide mortality valuation of all quantified impacts using an income elasticity of 1.0 is US$ 3 200 (US$ 800–5 400) per tonne of methane.
• Roughly 60 per cent, around 75 Mt/yr, of available targeted measures have low mitigation costs, and just over 50 per cent of those have negative costs – the measures pay for themselves quickly by saving money (Figure SDM2).
• Roughly 60 per cent of the available targeted measures have low mitigation costs, and just over 50 per cent of those have negative costs – the measures pay for themselves quickly by saving money (Figure SDM2).
• The greatest potential for negative cost abatement is in the oil and gas subsector where captured methane adds to revenue instead of being released to the atmosphere.
• The analysis shows that the average global mean surface temperature change over the 11–40-year period following emissions changes, ~34 per cent, is more uncertain than the ozone response, ~24 per cent.
• Methane’s short atmospheric lifetime means taking action now can quickly reduce atmospheric concentrations and result in similarly rapid reductions in climate forcing and ozone pollution.

Other Important Findings

• The greatest targeted abatement potential very likely lies within the fossil-fuel sector, for which average mitigation costs range from a high of ~US$1 250 per tonne of methane in the US EPA analysis to a net savings of ~US$ 400 per tonne in the IIASA analysis, with values in between those for the Harmsen and IEA analyses, the latter of which only considers the oil and gas subsectors. All these average costs are much lower than the per tonne societal benefits.
• Examining only targeted controls in the relatively robustly characterized fossil-fuel and waste sectors that cost less than the estimated societal benefits per tonne, the abatement potential is about 75 ±2 Mt/yr. Benefits from this level of abatement include ~0.13°C warming avoided in the 2040-2070 period, ~105 000 avoided premature deaths due to ozone exposure annually by 2030, and 11 Mt of avoided crop losses due primarily to ozone exposure each year. The benefits of the annually avoided premature deaths alone are estimated at US$ 190 billion (US$ 40–310 billion; 95 per cent confidence interval).
• Uncertainties exist along the entire chain from mitigation potential through physical responses to societal impacts. Overall uncertainties are likely to be primarily driven by limited understanding of climate sensitivity and of the effects of ozone exposure on human health, with generally small contributions from incomplete knowledge of mitigation potentials or in an understanding of the ozone response to methane emissions reductions. In some specific sectors or regions, however, limited knowledge of current emissions is probably a major driver of uncertainties in benefit-potential estimates.
• The findings in this assessment are the result of modeling that uses five state-of-the art global composition-climate models to evaluate changes in the Earth’s climate system and surface ozone concentrations from reductions in methane emissions. Results allow for rapid evaluation of impacts from methane emissions and the benefits from mitigation strategies to the climate and ground-level ozone formation and, air quality, public health, agricultural and other development benefits.
• The methane abatement that takes place in the all-sector all-pollutant climate change mitigation scenarios discussed in Section 4.1 is based in part on abatement cost curves that are incorporated within the IAMs. These encompass methane mitigation opportunities in multiple sectors at a variety of costs, which are examined in detail in this section.
• For the fossil fuel sector, the oil and gas subsector is the largest emitter, accounting for roughly two-thirds of the sector’s total emissions, with emissions from coal mining making up most of the remainder. Emissions from industry and transport are small, totalling ~7 Mt/yr, less than 2 per cent of anthropogenic emissions, from both categories (averaged across the four inventories).
• The analysis of methane emissions in IAMs not only explored the response in least-cost multi-pollutant pathways and in the carbon dioxide tax only pathways, but also examined the role of a cross-sector focus on methane (Harmsen et al. 2019b).
• Under a 2°C climate policy the models produce reductions in methane emissions from fossil fuels that are essentially as large as their maximum reduction potential. In contrast, reductions in emissions from agricultural subsectors – manure, enteric fermentation and rice cultivation – are lower than the maximum potential, whereas those for waste sewage and landfills are at the maximum in some models but lower in others.
• In addition to the benefits quantified here, methane reduction measures also contribute to multiple Sustainable Development Goals (SDGs), including climate action (SDG13), zero hunger (SDG2), good health and well-being (SDG3). Additionally, they provide cost reductions and efficiency gains in the private sector, create jobs, and stimulate technological innovation. (Sections 1.1, 4.4 and 5)

Limitations Noted in the Document

• Uncertainties exist along the entire chain from mitigation potential through physical responses to societal impacts. Overall uncertainties are likely to be primarily driven by limited understanding of climate sensitivity and of the effects of ozone exposure on human health, with generally small contributions from incomplete knowledge of mitigation potentials or in an understanding of the ozone response to methane emissions reductions. In some specific sectors or regions, however, limited knowledge of current emissions is probably a major driver of uncertainties in benefit-potential estimates.
• The analysis shows that the average global mean surface temperature change over the 11–40-year period following emissions changes, ~34 per cent, is more uncertain than the ozone response, ~24 per cent.
• For the fossil-fuel sector, average mitigation costs range from a high of ~US$1 250 per tonne of methane in the US EPA analysis to a net savings of ~US$ 400 per tonne in the IIASA analysis, with values in between those for the Harmsen and IEA analyses, the latter of which only considers the oil and gas subsectors.
• The results for ozone-related deaths show that national level values are greatest for countries with either or both large populations and high per person GDP, including China, India, Japan and the United States (Table 3.7 and Figure 3.15).
• The analysis of methane emissions in IAMs not only explored the response in least-cost multi-pollutant pathways and in the carbon dioxide tax only pathways, but also examined the role of a cross-sector focus on methane (Harmsen et al. 2019b). This was accomplished by imposing an economy-wide tax on methane emissions and examining how the models responded.
• There are substantial differences in sector-specific bottom-up methane emissions estimates created by different groups (Figure 2.1). This difference indicates that these estimates could be improved by additional work to better quantify activity levels for each source, and by improved quantification of source-specific emission factors which may vary substantially both between and within nations.

Conclusion

The study emphasizes the critical role of targeted control measures in reducing methane emissions across various sectors, highlighting the substantial benefits of these measures in terms of climate change mitigation, improved air quality, and health outcomes. The findings indicate that implementing such measures, with a particular focus on the fossil-fuel and waste sectors, can lead to significant reductions in emissions, with many controls available at a relatively low cost. This report illustrates how to do it, and the impact of their implementation. The analysis supports the implementation of methane-specific policies, which could lead to a rapid and substantial decrease in methane emissions, especially from coal, gas, and landfills, with abatement of livestock-related emissions highly model-dependent. The greatest targeted abatement potential very likely lies within the fossil-fuel sector. The study highlights the importance of behavioural changes and policy innovation to address agricultural sector methane emissions effectively. It also underscores the significance of reducing food waste and loss and the shift towards healthier diets, while recognizing the substantial barriers to implementation, including economic considerations and the need for strong policy intervention. The results underscore the urgent need for action and highlight the multiple benefits of methane mitigation across various domains. The study presents a vision for a more sustainable future that will require the collaboration of governments, businesses, and individuals. The analysis concludes with the potential for significant, cost-effective, and timely methane mitigation efforts, the study provides a solid foundation for further research and actions towards creating a climate-resilient and environmentally sustainable society. The results show that the models generally respond to a methane tax by most strongly reducing emissions from the energy sector, followed by land use, largely agriculture, and lastly the waste sector (Figure 4.13, top). Differences between the models are very large, however, especially for the land-use and waste sectors. The analysis also shows that the average global mean surface temperature change over the 11–40-year period following emissions changes, ~34 per cent, is more uncertain than the ozone response, ~24 per cent. (Figure 3.4). In the analysis using 2030 population and baseline mortality, the 50 per cent reduction in methane leads to 105 000 (66 000-140,000; 95 per cent confidence interval) fewer premature respiratory deaths and 81 000 (25 000-132 000; 95 per cent confidence interval) fewer cardiovascular deaths due to ozone exposure.