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ipcc ar6 wg3 – sources of global emissions & mitigation options by sector
*Post was originally written on April 4, 2022. You can find a twitter thread summary here. Most of this is summarized notes and quotes from the IPCC Sixth Assessment Report – Working Group III contribution. Working Group III: Mitigation of Climate Change.
The IPCC released The Working Group III (WG3) report earlier today, which provides an updated global assessment of climate change mitigation progress and pledges, and examines the sources of global emissions. This is the third and final part of the trilogy within the IPCC Sixth Assessment Report (AR6).
Compared to the other two AR6 reports which were more focused on the physical science basis and adaptation/vulnerability implications of Climate Change, WG3 provides emissions sources by sector and includes the evaluation of potential mitigation activities across sectors. This analysis can help inform our view of the overall potential of new decarbonization-focused sectors/technologies we are increasingly seeing companies invest capital into.
Below is a brief summary of some of the points I thought were most interesting.
sources of emissions and mitigation options by sector
- Emissions by Sector: Globally, GHG emissions continued to rise across all sectors and subsectors, and most rapidly in transport and industry (high confidence). In 2019, approximately 34% (20 GtCO2-eq) of total net anthropogenic GHG emissions came from the energy supply sector, 24% (14 GtCO2-eq) from industry, 22% [13 GtCO2-eq]from agriculture, forestry and other land use (AFOLU), 15% (8.7 GtCO2-eq) from transport and 6% (3.3 GtCO2-eq) from buildings. Once indirect emissions from energy use are considered, the relative shares of industry and buildings emissions rise to 34% and 17%, respectively.

Net Zero Pathways Require Substantial Direct and Indirect Mitigation Pathways: Quotes from the various sections below. There is a summary chart that lists out major mitigation options by sector, potential contribution to total net emissions reduction (measured on a GtCO2-equivalent basis), and estimated lifetime costs (the ones in blue are already economic).
- Energy: Net-zero CO2 energy systems entail: a substantial reduction in overall fossil fuel use, minimal use of unabated fossil fuels, and use of CCS in the remaining fossil system; electricity systems that emit no net CO2; widespread electrification of the energy system including end uses; energy carriers such as sustainable biofuels, low-emissions hydrogen, and derivatives in applications less amenable to electrification; energy conservation and efficiency; and greater physical, institutional, and operational integration across the energy system.
- Interesting datapoint: The combined global discounted value of the unburned fossil fuels and stranded fossil fuel infrastructure has been projected to be around 1–4 trillion dollars from 2015 to 2050 to limit global warming to approximately 2⁰C.
- AFOLU: The largest share of mitigation potential [4.2-7.4 GtCO2-eq] comes from the conservation, improved management, and restoration of forests and other ecosystems (coastal wetlands, peatlands, savannas and grasslands), with reduced deforestation in tropical regions having the highest total mitigation. Improved and sustainable crop and livestock management, and carbon sequestration in agriculture, the latter includes soil carbon management in croplands and grasslands, agroforestry and biochar, can contribute 1.8-4.1 GtCO2-eq reduction. Demand-side and material substitution measures, such as shifting to balanced, sustainable healthy diets, reducing food loss and waste, and using bio-materials, can contribute 1.1-3.6 GtCO2-eq reduction. In addition, demand-side measures together with the sustainable intensification of agriculture can reduce ecosystem conversion and CH4 and N2O emissions, and free-up land for reforestation and restoration, and the producing of renewable energy.
- Buildings: Integrated design approaches to the construction and retrofit of buildings have led to increasing examples of zero energy or zero carbon buildings in several regions. However, the low renovation rates and low ambition of retrofitted buildings have hindered the decrease of emissions. Mitigation interventions at the design stage include buildings typology, form, and multi-functionality to allow for adjusting the size of buildings to the evolving needs of their users and repurposing unused existing buildings to avoid using GHG-intensive materials and additional land. Mitigation interventions include: at the construction phase, low-emission construction materials, highly efficient building envelope and the integration of renewable energy solutions. The largest share of the mitigation potential of new buildings is available in developing countries while in developed countries the highest mitigation potential is within the retrofit of existing buildings.
- Transport: Substantial potential for GHG reductions, both direct and indirect, for the transport sector largely depends on power sector decarbonization, and low emissions feedstocks and production chains. Electric vehicles powered by low emissions electricity offer the largest decarbonization potential for land-based transport, on a life cycle basis. Costs of electrified vehicles, including automobiles, two and three wheelers, and buses are decreasing and their adoption is accelerating, but they require continued investments in supporting infrastructure to increase scale of deployment. Advances in battery technologies could facilitate the electrification of heavy-duty trucks and complement conventional electric rail systems. There are growing concerns about critical minerals needed for batteries. Material and supply diversification strategies, energy and material efficiency improvements, and circular material flows can reduce the environmental footprint and material supply risks for battery production. Low-GHG emissions hydrogen and hydrogen derivatives, including synthetic fuels, can offer mitigation potential in some contexts and land-based transport segments.
- For aviation, such technologies include high energy density, and low-emission hydrogen and synthetic fuels. Alternative fuels for shipping include low-emission hydrogen, ammonia, biofuels, and other synthetic fuels. Electrification could play a niche role for aviation and shipping for short trips and can reduce emissions from port and airport operations.
- Industry: Reducing industry emissions will entail coordinated action throughout value chains to promote all mitigation options, including demand management, energy and materials efficiency, circular material flows, as well as abatement technologies and transformational changes in production processes. Progressing towards net zero GHG emissions from industry will be enabled by the adoption of new production processes using low and zero GHG electricity, hydrogen, fuels, and carbon management. There are many sustainable options for demand management, materials efficiency, and circular material flows that can contribute to reduced emissions, but how these can be applied will vary across regions and different materials. These options have a potential for being more used in industrial practice and would need more attention from industrial policy.

- For the first-time, the IPCC included potential demand-side mitigation activities including shifting diets, transport patterns, and material efficiency. These could cut end-use emissions 40-70% by 2050 vs baseline scenarios.

Other interesting charts/points:
- Current Pledges are Not Enough to Limit Warming to Below 2°C: Pathways consistent with the implementation and extrapolation of countries’ current policies see leading to a median global warming estimate of 2.4°C to 3.5°C by 2100.
- Related, interesting data points:
- At least 18 countries have sustained production-based GHG and consumption-based CO2 emission reductions for longer than 10 years. Reductions were linked to energy supply decarbonization, energy efficiency gains, and energy demand reduction, which resulted from both policies and changes in economic structure.
- By 2020, there were ‘direct’ climate laws focused primarily on GHG reductions in 56 countries covering 53% of global emissions. Policy coverage remains limited for emissions from agriculture and the production of industrial materials and feedstocks.

- Need Deep, Rapid, and Sustained Emissions Reductions and Incredible Acceleration of Carbon Dioxide Removal in order for any pathways to 1.5°C or 2°C: All global modelled pathways that limit warming to 1.5°C (>50%) with no or limited overshoot, and those that limit warming to 2°C (>67%) involve rapid and deep and in most cases immediate GHG emission reductions in all sectors. The deployment of CDR to counterbalance hard-to-abate residual emissions is unavoidable if net zero CO2 or GHG emissions are to be achieved

- Decarbonization Technologies Can Scale Quickly When Unit Costs Come Down: From 2010–2019, there have been sustained decreases in the unit costs of solar energy (85%), wind energy (55%), and lithium-ion batteries (85%), and large increases in their deployment, e.g., >10x for solar and >100x for electric vehicles (EVs), varying widely across regions.
