The remaining carbon budget framework tracks progress towards the Paris Agreement’s goal to limit longer-term warming to well below 2 °C, but no analogous framework exists for constraining mid-century warming. Established single-basket methods of combining gases into CO2-equivalents using Global Warming Potentials (GWPs) lead to ambiguity over what combination of short- and long-lived emissions reductions are needed because they obscure the distinct warming impacts of each. We investigate to what extent a multi-basket approach that separates short-lived and long-lived pollutants can better estimate the likelihood for emission pathways to meet a near-term warming goal. We develop logistic regression models to categorize IPCC emission pathways (AR6) based on whether they exceed a mid-century temperature threshold. We focus on two baskets, using CO2 for long-lived and methane (CH4) for short-lived gases. For comparison, we consider several single-basket approaches (e.g. GWP100, GWP20, GWP*). We further apply our framework to a synthetic dataset covering a broader emissions space. Across both datasets, the two-basket outperforms all single-baskets. Using an illustrative near-term goal (1.7 °C), the two-basket approach reduces the magnitude of overshoot by a factor of 7 compared with the traditional single-basket. The two-basket’s advantage is smaller with the AR6 pathways, which we attribute to the high correlation between CO2 and CH4 emissions and confounding effects from other pollutants. Our results indicate that the two-basket approach better constrains overshoot magnitude, particularly if future emissions deviate from the AR6 assumption of correlated CO2 and CH4 reductions. Our approach allows the determination of a metric value and reduction target in the context of a chosen set of scenarios and temperature threshold; the outcome is a near-term methane-specific emissions budget that can be adopted by decisionmakers in a way that is analogous and complementary to the carbon budget. Future work could consider a third basket for very short-lived pollutants.
Anthropogenic methane (CH4) emissions increases from the period 1850–1900 until 2019 are responsible for around 65% as much warming as carbon dioxide (CO2) has caused to date, and large reductions in methane emissions are required to limit global warming to 1.5°C or 2°C. However, methane emissions have been increasing rapidly since ~2006. This study shows that emissions are expected to continue to increase over the remainder of the 2020s if no greater action is taken and that increases in atmospheric methane are thus far outpacing projected growth rates. This increase has important implications for reaching net zero CO2 targets: every 50 Mt CH4 of the sustained large cuts envisioned under low-warming scenarios that are not realized would eliminate about 150 Gt of the remaining CO2 budget. Targeted methane reductions are therefore a critical component alongside decarbonization to minimize global warming. We describe additional linkages between methane mitigation options and CO2, especially via land use, as well as their respective climate impacts and associated metrics. We explain why a net zero target specifically for methane is neither necessary nor plausible. Analyses show where reductions are most feasible at the national and sectoral levels given limited resources, for example, to meet the Global Methane Pledge target, but they also reveal large uncertainties. Despite these uncertainties, many mitigation costs are clearly low relative to real-world financial instruments and very low compared with methane damage estimates, but legally binding regulations and methane pricing are needed to meet climate goals.
Full citation: Shindell D, Sadavarte P, Aben I, Bredariol TdO, Dreyfus G, Höglund-Isaksson L, Poulter B, Saunois M, Schmidt GA, Szopa S, Rentz K, Parsons L, Qu Z, Faluvegi G and Maasakkers JD. The methane imperative. Front Sci (2024) 2:1349770. doi: 10.3389/fsci.2024.1349770
This IGSD Background Note summarizes the science supporting the need for fast climate mitigation to slow warming in the near term (2022–2041). It also describes the importance of cutting short-lived climate pollutants and protecting sinks in order to slow self-reinforcing feedbacks and avoid tipping points. It explains why winning a fast mitigation sprint to 2030 is critical for addressing the climate emergency and how the sprint complements the marathon to decarbonize the economy and achieve net-zero emissions.
Climate change poses an existential threat to humankind. The intertwined nature of climate change and human rights becomes apparent as we witness the adverse effects on various dimensions of human life. To address the climate emergency, we must slow down the rate of warming as much as possible as quickly as possible. Only a dual strategy to reduce both non-carbon dioxide super climate pollutants and carbon dioxide (CO2) can keep global temperatures within safe limits and protect human rights for present and future generations. This Brief outlines how the climate emergency is a challenge of temperature, tipping points, and time.
Also available in Spanish and Portuguese.
By phasing out production and consumption of most ozone-depleting substances (ODSs), the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) has avoided consequences of increased ultraviolet (UV) radiation and will restore stratospheric ozone to pre-1980 conditions by mid-century, assuming compliance with the phaseout. However, several studies have documented an unexpected increase in emissions and suggested unreported production of trichlorofluoromethane (CFC-11) and potentially other ODSs after 2012 despite production phaseouts under the Montreal Protocol. Furthermore, because most ODSs are powerful greenhouse gases (GHGs), there are significant climate protection benefits in collecting and destroying the substantial quantities of historically allowed production of chemicals under the Montreal Protocol that are contained in existing equipment and products and referred to as ODS “banks”. This technical note presents a framework for considering offsets to ozone depletion, climate forcing, and other environmental impacts arising from occurrences of unexpected emissions and unreported production of Montreal Protocol controlled substances, as recently experienced and likely to be experienced again. We also show how this methodology could be applied to the destruction of banks of controlled ODSs and GHGs or to halon or other production allowed under a Montreal Protocol Essential Use Exemption or Critical Use Exemption. Further, we roughly estimate the magnitude of offset each type of action could provide for ozone depletion, climate, and other environmental impacts that Montreal Protocol Parties agree warrant remedial action.
Fast action to mitigate non-CO2 climate pollutants, such as methane, including through implementing methane intensity requirements (such as via procurement specifications) for domestic and imported oil and gas, can have a significant role in reducing the likelihood of triggering catastrophic climate impacts as countries pursue carbon-neutrality goals. Without robust monitoring, reporting, and verification (MRV) of methane emissions, we will not be able to know the efficacy of methane mitigation policies and programs or whether we are meeting methane mitigation targets. Acting quickly to ensure that new investments in oil and gas infrastructure are built with enhanced MRV systems and methane intensity requirements in mind is essential to limiting risks of stranded assets and aligning with carbon-neutrality goals.
The ongoing and projected impacts from human-induced climate change highlight the need for mitigation approaches to limit warming in both the near term (<2050) and the long term (>2050). We clarify the role of non-CO2 greenhouse gases and aerosols in the context of near-term and long-term climate mitigation, as well as the net effect of decarbonization strategies targeting fossil fuel (FF) phaseout by 2050. Relying on Intergovernmental Panel on Climate Change radiative forcing, we show that the net historical (2019 to 1750) radiative forcing effect of CO2 and non-CO2 climate forcers emitted by FF sources plus the CO2 emitted by land-use changes is comparable to the net from non-CO2 climate forcers emitted by non-FF sources. We find that mitigation measures that target only decarbonization are essential for strong long-term cooling but can result in weak near-term warming (due to unmasking the cooling effect of coemitted aerosols) and lead to temperatures exceeding 2 °C before 2050. In contrast, pairing decarbonization with additional mitigation measures targeting short-lived climate pollutants and N2O, slows the rate of warming a decade or two earlier than decarbonization alone and avoids the 2 °C threshold altogether. These non-CO2 targeted measures when combined with decarbonization can provide net cooling by 2030 and reduce the rate of warming from 2030 to 2050 by about 50%, roughly half of which comes from methane, significantly larger than decarbonization alone over this time frame. Our analysis demonstrates the need for a comprehensive CO2 and targeted non-CO2 mitigation approach to address both the near-term and long-term impacts of climate disruption.
Scientific studies show that fast actions to reduce near-term warming are essential to slowing self-reinforcing climate feedbacks and avoiding irreversible tipping points. Yet cutting CO2 emissions only marginally impacts near-term warming. This study identifies two of the most effective mitigation strategies to limit near-term warming beyond CO2 mitigation, namely reducing short-lived climate pollutants (SLCPs) and promoting targeted nature-based solutions (NbS), and comprehensively reviews the latest scientific progress in these fields. Studies show that quickly reducing SLCP emissions, particularly hydrofluorocarbons (HFCs), methane, and black carbon, from all relevant sectors can avoid up to 0.6 °C of warming by 2050. Additionally, promoting targeted NbS that protect and enhance natural carbon sinks, including in forests, wetlands, grasslands, and agricultural lands, can avoid emissions of 23.8 Gt of CO2e per year in 2030, without jeopardizing food security and biodiversity. Based on the scientific evidence, the paper provided a series of policy recommendations on SLCPs and NbS.
Chapter 25 in Health of People, Health of Planet and Our Responsibility: Climate Change, Air Pollution and Health (Al-Delaimy, W. K., Ramanathan, & V., Sorondo, M. S. eds). Springer, Cham. Pages 321-331.
Climate change is becoming an existential threat with warming in excess of 2 °C within the next three decades and 4–6 °C within the next several decades. Warming of such magnitudes will expose as many as 75% of the world’s population to deadly heat stress in addition to disrupting the climate and weather worldwide. Climate change is an urgent problem requiring urgent solutions. This chapter lays out urgent and practical solutions that are ready for implementation now, will deliver benefits in the next few critical decades, and place the world on a path to achieving the long-term targets of the Paris Agreement. The approach consists of four building blocks and three levers to implement ten scalable solutions described in this chapter. These solutions will enable society to decarbonize the global energy system by 2050 through efficiency and renewables, drastically reduce short-lived climate pollutants, and stabilize the warming well below 2 °C both in the near term (before 2050) and in the long term (after 2050). The solutions include an atmospheric carbon extraction lever to remove CO2 from the air. The amount of CO2 that must be removed ranges from negligible (if the emissions of CO2 from the energy system and short-lived climate pollutants have started to decrease by 2020 and carbon neutrality is achieved by 2050) to a staggering one trillion tons (if the carbon lever is not pulled and emissions of climate pollutants continue to increase until 2030).
Chapter 15: Technologies for Super Pollutant Mitigation
The chapter explore a complementary climate solution to CO2 reductions: reducing a key group of warming agents knows as super pollutants or short-lived climate pollutants (SLCPs) to bend the warming curve quickly (over a few decades) while we pursue CO2 mitigation to bend the curve in the long term (over several decades to centuries). Combined, these efforts, if enacted by 2020, give us a significant chance (about 90% probability) of keeping warming well below 2°C (aiming for 1.5°C) in this century and beyond. Mitigation of SLCPs, if completed by 2030, can bend the warming curve by up to 0.6°C by 2050 (about 0.4°C from methane mitigation, 0.1°C from black carbon, and 0.1°C from HFCs), cutting the rate of projected warming by about half compared with “business as usual” and reducing the projected sea level rise between 2020 and 2050 by 20%.
