Most climate change mitigation strategies focus on reducing CO2 emissions. However, non-CO2 greenhouse gases and other anthropogenic climate drivers, though less abundant than CO2, can be more powerful climate warmers. This Voices asks, “What are the important actions to reduce non-CO2 warming forcers to help the world reach Paris Agreement targets?” Most climate change mitigation strategies focus on reducing CO2 emissions. However, non-CO2 greenhouse gases and other anthropogenic climate drivers, though less abundant than CO2, can be more powerful climate warmers. This Voices asks, “What are the important actions to reduce non-CO2 warming forcers to help the world reach Paris Agreement targets?” The perennially cold temperatures that characterize permafrost soils stabilize globally significant carbon and nitrogen stores, despite covering just ∼15% of the Earth’s surface. These frozen soils formed due to a combination of climatic and ecological conditions; however, belowground temperatures are now on the rise across circumpolar regions prompting permafrost thaw events. Considerable research has examined post-thaw CO2 dynamics, with uncertainties remaining if permafrost systems will continue to serve as an important CO sink or transition into a source. Permafrost thaw events also impact non-CO2 greenhouse gas production, including CH4 and N2O – greenhouse gases with radiative forcings 25 to 100 times greater than CO2, respectively. When ice-rich permafrost thaws, rapid changes in hydrologic conditions and soil structure integrity can cause these systems to transition from relatively dry permafrost forests into wetland features known as thermokarst. Thermokarst has been identified as a hotspot for both CH and NO production, especially in the initial years following thaw. As climate conditions continue to warm, ecological systems that protect permafrost will become increasingly important to limit enhanced thermokarst formation. As part of a cohesive climate change mitigation strategy, a paradigm shift is needed in how we value and manage northern ecosystems moving forward. Increased recognition of the long-term climate mitigation benefits from conservation and restoration of many northern ecosystems, including systems that protect permafrost, is an important first step to limiting natural sources of non-CO2 greenhouse gas emissions in the coming century. It should be clear to all who participated in COP27 that most progress on climate change is happening outside of the COPs. This includes the Global Methane Pledge, which now has 150 countries aiming to reduce global methane emissions 30% below 2020 levels by 2030. The Pledge is an important start for cutting methane emissions to slow near-term warming by avoiding nearly 0.3°C of warming by the 2040s. The Pledge should be followed by a mandatory Global Methane Agreement inspired by the world’s best environmental treaty, the Montreal Protocol, a sectoral agreement that, in addition to healing the ozone layer, has also avoided as much warming as carbon dioxide has caused and is on course to avoid 2.5°C of warming by 2100. The Montreal Protocol shows the value of disaggregating the climate problem into manageable sectors. By tailoring the governance approach to one sector, the Protocol took a bite out of the climate problem, started modestly, learned by doing, gained confidence, and repeatedly strengthened its mandatory measures to speed phaseouts. Its success is also based on robust implementation of the principle of “common but differentiated responsibilities,” including funding for agreed incremental cost of developing-country compliance. Its real-time assessment of the relevant science and technologies enables fast shifts to safe solutions. Because cutting methane emissions is the only known way to slow self-reinforcing feedback loops and avoid irreversible tipping points lurking beyond 1.5°C, the effort belongs at head-of-state level. At upcoming G7 and G20 meetings, countries representing 75% of global emissions and 80% of global GDP can get a head start to keep the 1.5°C target alive by committing to a Global Methane Agreement. Among the non-CO2 gases, short-lived climate forcers (SLCFs) are gaining attention due to their significant near-term climate impacts. Recent studies have urged mitigating SLCFs given their potential to avoid a 0.5°C rise in global temperatures by mid-century. However, SLCFs comprise a complex mix of warming and cooling forcers. For example, efforts to reduce CO2 emissions from formal sectors like power plants and industry often concurrently reduce emissions of air pollutants, like SO2 and NOx, that are also cooling SLCFs. Thus, the climate mitigation impact of reducing CO2 emissions is weakened. Fortunately, there are opportunities to reduce emissions of warming SLCFs, like black carbon, that benefit air quality while reducing climate warming. Inefficient combustion practices such as biomass fuels for cooking and heating, kerosene lamps for lighting, open-field burning of crop residues, and traditional technologies for brick manufacturing all have powerful warming impacts via SLCF emissions. Targeting mitigation in these informal sectors has significant potential for climate benefits in the near-term, even greater than CO2 mitigation. Furthermore, these activities are more common in developing nations and mitigation would have significant health benefits by reducing air pollution. Black carbon mitigation actions must precede, or at least be implemented in conjunction with, CO2-targeted climate actions in formal sectors to avoid counter-productively increasing warming by reducing the emissions of cooling forcers. One challenge is these mitigation efforts mostly fall under the governance umbrella of air-quality, which is more of a regional issue than a global one and thus lacks stringent international monitoring. It is imperative that climate policy makers identify activities. The impact of non-CO2 greenhouse gases (GHGs) has been silenced in the news but remains a key piece of the cake with upmost importance in the battle against climate change. Among them, fluorinated gases (F-gases), such as hydrofluorocarbons (HFCs), are common substances used in home and industry refrigeration, with a global warming potential (GWP) that may be several orders of magnitude higher than that of CO2, with an expected contribution of around 0.25–0.4°C increase of the Earth global temperature by 2050. While the Kigali Amendment, accompanied by the strict 517/2014 European regulation and the American Aim Act, established an international framework aimed at reducing F-gas emissions up to 80% in 25–30 years, the intrinsic nature of F-gases creates a challenge in finding ideal substitutes: lower GWP alternatives, e.g., hydrofluorolefins (HFOs), are not exempt from technical difficulties and flammability issues. A mid-term solution can adopt a circular approach to recycle F-gases from end-of-life refrigeration devices (e.g., KET4F-Gas). The high difficulty of recycling mixed F-gases has been overcome by a few recently developed breakthrough separation technologies, including adsorption on activated carbons, zeolites, and metallic organic frameworks (MOFs); absorption in environmentally friendly solvents; and membrane separation. The unique value of these techniques will not only avoid the massive production of new HFCs but also maintain the refrigeration needs. The combination of these technologies, along with the design of a new generation of sustainable refrigerants, seem to be the most realistic path that contributes to stopping the devastating consequences of global warming caused by non-CO2 F-gas emissions. The oil and gas sector is responsible for 25% of global methane emissions and represents a key opportunity for near-term climate action. Global interest in methane mitigation has led to a rise in voluntary initiatives on low-leakage or responsible gas certifications for companies that demonstrate emissions reductions. While this is a welcome development that can complement regulatory actions, caution about the reliability of these certifications is warranted. The key for such voluntary initiatives to succeed is trust among regulators, companies, the scientific community, and the public. Three key elements are necessary to build trust. First, recent work has demonstrated significant spatial and temporal variation in methane emissions. Finding and fixing high-volume, intermittent emission events is key to effective mitigation. This requires high-frequency and multi-tiered measurement approaches using well-characterized technologies such as satellites, aerial surveys, or continuous emissions monitoring systems. Second, measurements do not imply information that can lead to emissions reductions. Information—such as a more accurate emissions inventory estimate or identifying whether an emission is repairable—require interpretation. Interpreting measurements must be done consistently across space, time, and technologies, using transparent, peer-reviewed, and publicly available analytical frameworks. Third, certification must be verifiable by experts who can independently evaluate measurement and operational data and provide confidence in reported emissions. Voluntary initiatives can result in a beneficial race-to-the-bottom on methane, helping achieve the Global Methane Pledge mitigation targets, but it will only work in a world guided by the best available science and sector-wide transparency. Methane is produced from a variety of agricultural sources with one of the most prominent being methane formed in the gut of ruminant animals such as cattle and sheep. While many strategies have been investigated to address the methane formed in animals, the methane from animal manure during manure management has received much less attention despite its importance in countries with highly intensive animal husbandry. Considering that in 2012, 1.7% of the total greenhouse gas emissions in the European Union were related to manure management, it is imperative that strategies for the reduction of methane emissions from animal manure are developed. The treatment of manure is challenging due to the large amounts of manure produced annually, the low monetary value of manure, and the decentralized production of livestock. Traditionally the value of manure has been its use as cheap fertilizer in place of expensive synthetic fertilizers. When developing new solutions, it is important to ensure that existing as well as new technologies within manure treatment are effectively adopted by the farmers. Technologies need to be cheap and easily implemented in already existing animal productions with clear advantages to the individual farmer. Utilizing manure for biogas production is an example of a technology that adds value to the manure as farmers are paid for the produced biogas and that is easily implemented in existing productions. However, a substantial investment is required to build the needed biogas plants, and solutions are needed to address methane emissions prior to biogas production. Inhibiting methane formation in manure already at the livestock-housing level using cheap, safe, and biogas-compatible plant waste materials from other industries could be a possible way forward. Rice, a vital staple food, feeds half of the world’s population, especially in Asia, Latin America, and parts of Africa. However, rice cultivation is a major driver for global warming that accounts for approximately 12% of the global anthropogenic methane (CH4) emitted from rice paddy fields. Rice is cultivated under different water regimes, with irrigated continuously flooded, rainfed lowland, and deep-water rice ecosystems as the major contributors to CH4 during the process of methanogenesis. Alternate wetting and drying, and direct seeded methods of paddy cultivation, can reduce CH4 emission by 40%–50% over transplanted continuously flooded rice. However, such water management measures are not possible in rainfed lowland and deep-water paddy systems. Amendments such as phosphogypsum (a waste by-product of fertilizer industry containing sulphate) can enable sulphate reducers to outcompete methanogens, resulting in CH4 emissions reduction by 10%–20%. Methane-oxidizing bacteria or methanotrophs can also reduce CH4 by another 10%–20%. Furthermore, application of carrier-based formulation of plant-growth-promoting and methane-oxidizing bacteria, and integratinge them with biofertilizer application in rice cultivation, can not only mitigate CH4 but also reduce the crop nitrogen fertilizer use and therefore N2O emissions. A leaf color chart, a cost-effective tool for nitrogen fertilizer application in rice cultivation can further help to mitigate N2O and also reduce ammonia volatilization. Application of natural nitrification inhibitors such as neem oil coated over urea fertilizer can also lessen both N2O and CH4 emissions. A strategic deployment of these approaches will reduce greenhouse gas intensity of paddy cultivation, further helping to achieve the targets of net-zero emissions and alleviate the global warming potential. A.R. has current research support from natural-gas producers, the US Department of Energy, State of New York, and Environmental Defense Fund. The author serves on the US Department of Transportation’s Pipeline Advisory Committee, a member of the US Department of Energy's National Petroleum Council Study Committee. The studies referred to in K.T.’s contribution were carried out by the author at Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, India with funding from the Indian Ministry of Environment Forest and Climate Change under the NCAP-COALESCE project. S.S. has a patent, “Mitigation of ammonia, odor and greenhouse gases,” pending to University of Southern Denmark (PCT/EP2020/052622).
Search from 250 M+ research papersSearch from 250 M+ research papers
Just Published
Apr 17, 2024
Ficawoyi Donou-Adonsou + 13
Open Access