Improved calculation of warming-equivalent emissions for short-lived climate pollutants

Improving Human Diets and Welfare through Using Herbivore-Based Foods: 2. Environmental Consequences and Mitigations

Animal-sourced foods are important for human nutrition and health, but they can have a negative impact on the environment. These impacts can result in land use tensions associated with population growth and the loss of native forests and wetlands during agricultural expansion. Increased greenhouse gas emissions, and high water use but poor water quality outcomes can also be associated. Life cycle analysis from cradle-to-distribution has shown that novel plant-based meat alternatives can have an environmental footprint lower than that of beef finished in feedlots, but higher than for beef raised on well-managed grazed pastures. However, several technologies and practices can be used to mitigate impacts. These include ensuring that grazing occurs when feed quality is high, the use of dietary additives, breeding of animals with higher growth rates and increased fecundity, rumen microbial manipulations through the use of vaccines, soil management to reduce nitrous oxide emission, management systems to improve carbon sequestration, improved nutrient use efficacy throughout the food chain, incorporating maize silage along with grasslands, use of cover crops, low-emission composting barns, covered manure storages, and direct injection of animal slurry into soil. The technologies and systems that help mitigate or actually provide solutions to the environmental impact are under constant refinement to enable ever-more efficient production systems to allow for the provision of animal-sourced foods to an ever-increasing population.

Environmental assessment of diets: overview and guidance on indicator choice

Comprehensive but interpretable assessment of the environmental performance of diets involves choosing a set of appropriate indicators. Current knowledge and data gaps on the origin of dietary foodstuffs restrict use of indicators relying on site-specific information. This Personal View summarises commonly used indicators for assessing the environmental performance of diets, briefly outlines their benefits and drawbacks, and provides recommendations on indicator choices for actors across multiple fields involved in activities that include the environmental assessment of diets. We then provide recommendations on indicator choices for actors across multiple fields involved in activities that use environmental assessments, such as health and nutrition experts, policy makers, decision makers, and private-sector and public-sector sustainability officers. We recommend that environmental assessment of diets should include indicators for at least the five following areas: climate change, biosphere integrity, blue water consumption, novel entities, and impacts on natural resources (especially wild fish stocks), to capture important environmental trade-offs. If more indicators can be handled in the assessment, indicators to capture impacts related to land use quantity and quality and green water consumption should be used. For ambitious assessments, indicators related to biogeochemical flows, stratospheric ozone depletion, and energy use can be added.

Curbing methane emissions from Italian cattle farms. An agroeconomic modelling simulation of alternative policy tools

Methane (CH4) emissions from cattle farms have been prioritised on the EU agenda, as shown by recent legislative initiatives. This study employs a supply-side agroeconomic model that mimics the behaviour of heterogeneous individual farms to simulate the application of alternative economic policy instruments to curb CH4 emissions from Italian cattle farms, as identified by the 2020 Farm Accountancy Data Network survey. Simulations consider increasing levels of a tax on each tonne of CH4 emitted or of a subsidy paid for each tonne of CH4 curbed with respect to the baseline. Individual marginal abatement costs are also derived. Besides, to consider possible technological options to curb emissions, a mitigation strategy is simulated, with different levels of costs and benefits to appraise the potential impacts on the sector. Relevant reductions in operating income are foreseen, the most substantial in farm types and size classes characterised by lower levels of carbon productivity. The introduction of the mitigation strategy shows that the outcome in terms of mitigation potential, without undermining production level, highly depends on the implementation costs, but can also vary widely due to heterogeneous farms' economic performances. Policy implications are also derived.

Impacts of reduced synthetic fertiliser use under current and future climates: Exploration using integrated agroecosystem modelling in the upper River Taw observatory, UK

The intensification of farming and increased nitrogen fertiliser use, to satisfy the growing population demand, contributed to the extant climate change crisis. Use of synthetic fertilisers in agriculture is a significant source of anthropogenic Greenhouse Gas (GHG) emissions, especially potent nitrous oxide (N2O). To achieve the ambitious policy target for net zero by 2050 in the UK, it is crucial to understand the impacts of potential reductions in fertiliser use on multiple ecosystem services, including crop production, GHG emissions and soil organic carbon (SOC) storge. A novel integrated modelling approach using three established agroecosystem models (SPACSYS, CSM and RothC) was implemented to evaluate the associated impacts of fertiliser reduction (10%, 30% and 50%) under current and projected climate scenarios (RCP2.6, RCP4.5 and RCP8.5) in a study catchment in Southwest England. 48 unique combinations of soil types, climate conditions and fertiliser inputs were evaluated for five major arable crops plus improved grassland. With a 30% reduction in fertiliser inputs, the estimated yield loss under current climate ranged between 11% and 30% for arable crops compared with a 20-24% and 6-22% reduction in N2O and methane emissions, respectively. Biomass was reduced by 10-25% aboveground and by <12% for the root system. Relative to the baseline scenario, soil type dependent reductions in SOC sequestration rates are predicted under future climate with reductions in fertiliser inputs. Losses in SOC were more than doubled under the RCP4.5 scenario. The emissions from energy use, including embedded emissions from fertiliser manufacture, was a significant source (14-48%) for all arable crops and the associated GWP20.

Perspective: science and the future of livestock industries

Since the 1990s, livestock industries have been forced to respond to major pressures from society, particularly with respect to methane emissions and animal welfare. These challenges are exacerbated by the inevitability of global heating and the effects it will have on livestock productivity. The same challenges also led to questions about the value of animal-sourced foods for feeding the world. The industries and the research communities supporting them are meeting those challenges. For example, we can now envisage solutions to the ruminant methane problem and those solutions will also improve the efficiency of meat and milk production. Animal welfare is a complex mix of health, nutrition and management. With respect to health, the 'One Health' concept is offering better perspectives, and major diseases, such as helminth infection, compounded by resistance against medication, are being resolved through genetic selection. With respect to nutrition and stress, 'fetal programming' and the epigenetic mechanisms involved offer novel possibilities for improving productivity. Stress needs to be minimized, including stress caused by extreme weather events, and solutions are emerging through technology that reveals when animals are stressed, and through an understanding of the genes that control susceptibility to stress. Indeed, discoveries in the molecular biology of physiological processes will greatly accelerate genetic progress by contributing to genomic solutions. Overall, the global context is clear - animal-sourced food is an important contributor to the future of humanity, but the responses of livestock industries must involve local actions that are relevant to geographical and socio-economic constraints.

Feasibility of mitigation measures for agricultural greenhouse gas emissions in the UK. A systematic review

The UK Government has set an ambitious target of achieving a national "net-zero" greenhouse gas economy by 2050. Agriculture is arguably placed at the heart of achieving net zero, as it plays a unique role as both a producer of GHG emissions and a sector that has the capacity via land use to capture carbon (C) when managed appropriately, thus reducing the concentration of carbon dioxide (CO2) in the atmosphere. Agriculture's importance, particularly in a UK-specific perspective, which is also applicable to many other temperate climate nations globally, is that the majority of land use nationwide is allocated to farming. Here, we present a systematic review based on peer-reviewed literature and relevant "grey" reports to address the question "how can the agricultural sector in the UK reduce, or offset, its direct agricultural emissions at the farm level?" We considered the implications of mitigation measures in terms of food security and import reliance, energy, environmental degradation, and value for money. We identified 52 relevant studies covering major foods produced and consumed in the UK. Our findings indicate that many mitigation measures can indeed contribute to net zero through GHG emissions reduction, offsetting, and bioenergy production, pending their uptake by farmers. While the environmental impacts of mitigation measures were covered well within the reviewed literature, corresponding implications regarding energy, food security, and farmer attitudes towards adoption received scant attention. We also provide an open-access, informative, and comprehensive dataset for agri-environment stakeholders and policymakers to identify the most promising mitigation measures. This research is of critical value to researchers, land managers, and policymakers as an interim guideline resource while more quantitative evidence becomes available through the ongoing lab-, field-, and farm-scale trials which will improve the reliability of agricultural sustainability modelling in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13593-023-00938-0.

What is the climate footprint of therapeutic diets for people with chronic kidney disease? Results from an Australian analysis

BACKGROUND

Immediate action is needed to stabilise the climate. Dietitians require knowledge of how the therapeutic diets they prescribe may contribute to climate change. No previous research has quantified the climate footprint of therapeutic diets. This study sought to quantify and compare the climate footprint of two types of therapeutic diets for people with chronic kidney disease (CKD) with two reference diets.

METHODS

A usual diet for an individual with CKD and a novel plant-based diet for CKD were compared with the current Australian diet and the Australian-adapted EAT Lancet Planetary Health Diet (PHD). The climate footprint of these diets was measured using the Global Warming Potential (GWP*) metric for a reference 71-year-old male.

RESULTS

No diets analysed were climate neutral, and therefore, all contribute to climate change. The novel plant-based diet for CKD (1.20 kg carbon dioxide equivalents [CO2 e] per day) produced 35% less CO2 e than the usual renal diet for an individual with CKD (1.83 kg CO2 e per day) and 50% less than the current Australian diet (2.38 kg CO2 e per day). The Australian-adapted EAT Lancet PHD (1.04 kg CO2 e per day) produced the least amount of CO2 e and 56% less than the current Australian diet. The largest contributors to the climate footprint of all four diets were foods from the meats and alternatives, dairy and alternatives and discretionary food groups.

CONCLUSIONS

Dietetic advice to reduce the climate footprint of therapeutic diets for CKD should focus on discretionary foods and some animal-based products. Future research is needed on other therapeutic diets.

Practical Guide to Measuring Wetland Carbon Pools and Fluxes

Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13157-023-01722-2.

Risk to rely on soil carbon sequestration to offset global ruminant emissions

Carbon sequestration in grasslands has been proposed as an important means to offset greenhouse gas emissions from ruminant systems. To understand the potential and limitations of this strategy, we need to acknowledge that soil carbon sequestration is a time-limited benefit, and there are intrinsic differences between short- and long-lived greenhouse gases. Here, our analysis shows that one tonne of carbon sequestrated can offset radiative forcing of a continuous emission of 0.99 kg methane or 0.1 kg nitrous oxide per year over 100 years. About 135 gigatonnes of carbon is required to offset the continuous methane and nitrous oxide emissions from ruminant sector worldwide, nearly twice the current global carbon stock in managed grasslands. For various regions, grassland carbon stocks would need to increase by approximately 25% - 2,000%, indicating that solely relying on carbon sequestration in grasslands to offset warming effect of emissions from current ruminant systems is not feasible.

Curbing global solid waste emissions toward net-zero warming futures

No global analysis has considered the warming that could be averted through improved solid waste management and how much that could contribute to meeting the Paris Agreement's 1.5° and 2°C pathway goals or the terms of the Global Methane Pledge. With our estimated global solid waste generation of 2.56 to 3.33 billion tonnes by 2050, implementing abrupt technical and behavioral changes could result in a net-zero warming solid waste system relative to 2020, leading to 11 to 27 billion tonnes of carbon dioxide warming-equivalent emissions under the temperature limits. These changes, however, require accelerated adoption within 9 to 17 years (by 2033 to 2041) to align with the Global Methane Pledge. Rapidly reducing methane, carbon dioxide, and nitrous oxide emissions is necessary to maximize the short-term climate benefits and stop the ongoing temperature rise.

A bio-augmented system with Methylosarcina sp. LC-4 immobilized on bio-carriers: Towards an integrated approach to mitigate and valorize methane emissions from landfills to biodiesel

Bio-augmented systems based on methanotrophs are indispensable in curbing anthropogenic methane emissions from engineered landfills or dumpsites to curtail rising levels of greenhouse gases. Using a defined methanotroph culture immobilized on an inert material-based bio-carrier makes it possible to harness these methane emissions for creating value-added products, thus contributing to the circular bio-economy. The methane oxidation capacity of the model methanotroph Methylosarcina sp. LC-4, a prospective organism for biodiesel production using methane present in landfill gas, immobilized on several inert bio-carriers, was evaluated to identify a bio-carrier that provided optimum conditions for the process. Among the several bio-carriers evaluated, perlite and vermiculite were selected due to their high specific surface area and superior water-holding capacity, which result in the retention of nutrients and biomass and higher methane elimination capacity. While perlite showed high biomass holding capacity and methane transport, vermiculite supported a high growth of methanotrophs. LC-4 immobilized on perlite and vermiculite as the bio-carrier showed maximum methane elimination capacity (MEC) of 291.3 g m-2 day-1 and 155.5 g m-2 day-1, respectively. The low bed height of only 0.13 m and a short start-up period of 2-4 days are promising for use as alternate daily cover in a landfill. The recovered biomass had 12% (w/w) fatty acid methyl ester (FAME), with a high fraction of (∼85%) of C14-C18 saturated and monounsaturated fatty acids, suitable for biodiesel production. The combination of perlite and vermiculite increased MEC and FAME content levels. The current study demonstrated a new bio-augmented system designed with a pure methanotroph for methane elimination with a short start-up time and the valorization of the assimilated methane.

Retrospective and projected warming-equivalent emissions from global livestock and cattle calculated with an alternative climate metric denoted GWP

Limiting warming by the end of the century to 1.5°C compared to pre-Industrial times requires reaching and sustaining net zero global carbon dioxide (CO2) emissions and declining radiative forcing from non-CO2 greenhouse gas (GHG) sources such as methane (CH4). This implies eliminating CO2 emissions or balancing them with removals while mitigating CH4 emissions to reduce their radiative forcing over time. The global cattle sector (including Buffalo) mainly emits CH4 and N2O and will benefit from understanding the extent and speed of CH4 reductions necessary to align its mitigation ambitions with global temperature goals. This study explores the utility of an alternative usage of global warming potentials (GWP*) in combination with the Transient Climate Response to cumulative carbon Emissions (TCRE) to compare retrospective and projected climate impacts of global livestock emission pathways with other sectors (e.g. fossil fuel and land use change). To illustrate this, we estimated the amount and fraction of total warming attributable to direct CH4 livestock emissions from 1750 to 2019 using existing emissions datasets and projected their contributions to future warming under three historical and three future emission scenarios. These historical and projected estimates were transformed into cumulative CO2 equivalent (GWP100) and warming equivalent (GWP*) emissions that were multiplied by a TCRE coefficient to express induced warming as globally averaged surface temperature change. In general, temperature change estimates from this study are comparable to those obtained from other climate models. Sustained annual reductions in CH4 emissions of 0.32% by the global cattle sector would stabilize their future effect on global temperature while greater reductions would reverse historical past contributions to global warming by the sector in a similar fashion to increasing C sinks. The extent and speed with which CH4 mitigation interventions are introduced by the sector will determine the peak temperature achieved in the path to net-zero GHG.

Blue and green ammonia production: A techno-economic and life cycle assessment perspective

Blue and green ammonia production have been proposed as low-carbon alternatives to emissions-intensive conventional ammonia production. Although much attention has been given to comparing these alternatives, it is still not clear which process has better environmental and economic performance. We present a techno-economic analysis and full life cycle assessment to compare the economics and environmental impacts of blue and green ammonia production. We address the importance of time horizon in climate change impact comparisons by employing the Technology Warming Potential, showing that methane leakage can exacerbate the climate change impacts of blue ammonia in short time horizons. We represent a constrained renewable electricity availability scenario by comparing the climate change impact mitigation efficiency per kWh of renewable electricity. Our work emphasizes the importance of maintaining low natural gas leakage for sustainability of blue ammonia, and the potential for technological advances to further reduce the environmental impacts of photovoltaics-based green ammonia.

Are single global warming potential impact assessments adequate for carbon footprints of agri-food systems?

The vast majority of agri-food climate-based sustainability analyses use global warming potential (GWP100) as an impact assessment, usually in isolation; however, in recent years, discussions have criticised the 'across-the-board' application of GWP100 in Life Cycle Assessments (LCAs), particularly of food systems which generate large amounts of methane (CH4) and considered whether reporting additional and/or alternative metrics may be more applicable to certain circumstances or research questions (e.g. Global Temperature Change Potential (GTP)). This paper reports a largescale sensitivity analysis using a pasture-based beef production system (a high producer of CH4 emissions) as an exemplar to compare various climatatic impact assessments: CO2-equivalents using GWP100 and GTP100, and 'CO2-warming-equivalents' using 'GWP Star', or GWP*. The inventory for this system was compiled using data from the UK Research and Innovation National Capability, the North Wyke Farm Platform, in Devon, SW England. LCAs can have an important bearing on: (i) policymakers' decisions; (ii) farmer management decisions; (iii) consumers' purchasing habits; and (iv) wider perceptions of whether certain activities can be considered 'sustainable' or not; it is, therefore, the responsibility of LCA practitioners and scientists to ensure that subjective decisions are tested as robustly as possible through appropriate sensitivity and uncertainty analyses. We demonstrate herein that the choice of climate impact assessment has dramatic effects on interpretation, with GWP100 and GTP100 producing substantially different results due to their different treatments of CH4 in the context of carbon dioxide (CO2) equivalents. Given its dynamic nature and previously proven strong correspondence with climate models, out of the three assessments covered, GWP* provides the most complete coverage of the temporal evolution of temperature change for different greenhouse gas emissions. We extend previous discussions on the limitations of static emission metrics and encourage LCA practitioners to consider due care and attention where additional information or dynamic approaches may prove superior, scientifically speaking, particularly in cases of decision support.

How to make climate-neutral aviation fly

The European aviation sector must substantially reduce climate impacts to reach net-zero goals. This reduction, however, must not be limited to flight CO₂ emissions since such a narrow focus leaves up to 80% of climate impacts unaccounted for. Based on rigorous life-cycle assessment and a time-dependent quantification of non-CO₂ climate impacts, here we show that, from a technological standpoint, using electricity-based synthetic jet fuels and compensating climate impacts via direct air carbon capture and storage (DACCS) can enable climate-neutral aviation. However, with a continuous increase in air traffic, synthetic jet fuel produced with electricity from renewables would exert excessive pressure on economic and natural resources. Alternatively, compensating climate impacts of fossil jet fuel via DACCS would require massive CO₂ storage volumes and prolong dependence on fossil fuels. Here, we demonstrate that a European climate-neutral aviation will fly if air traffic is reduced to limit the scale of the climate impacts to mitigate.

Review: Harnessing extant energy and protein requirement modeling for sustainable beef production

Numerous mathematical nutrition models have been developed in the last sixty years to predict the dietary supply and requirement of farm animals' energy and protein. Although these models, usually developed by different groups, share similar concepts and data, their calculation routines (i.e., submodels) have rarely been combined into generalized models. This lack of mixing submodels is partly because different models have different attributes, including paradigms, structural decisions, inputs/outputs, and parameterization processes that could render them incompatible for merging. Another reason is that predictability might increase due to offsetting errors that cannot be thoroughly studied. Alternatively, combining concepts might be more accessible and safer than combining models' calculation routines because concepts can be incorporated into existing models without changing the modeling structure and calculation logic, though additional inputs might be needed. Instead of developing new models, improving the merging of extant models' concepts might curtail the time and effort needed to develop models capable of evaluating aspects of sustainability. Two areas of beef production research that are needed to ensure adequate diet formulation include accurate energy requirements of grazing animals (decrease methane emissions) and efficiency of energy use (reduce carcass waste and resource use) by growing cattle. A revised model for energy expenditure of grazing animals was proposed to incorporate the energy needed for physical activity, as the British feeding system recommended, and eating and rumination (HjEer) into the total energy requirement. Unfortunately, the proposed equation can only be solved iteratively through optimization because HjEer requires metabolizable energy (ME) intake. The other revised model expanded an existing model to estimate the partial efficiency of using ME for growth (kg) from protein proportion in the retained energy by including an animal degree of maturity and average daily gain (ADG) as used in the Australian feeding system. The revised kg model uses carcass composition, and it is less dependent on dietary ME content, but still requires an accurate assessment of the degree of maturity and ADG, which in turn depends on the kg. Therefore, it needs to be solved iteratively or using one-step delayed continuous calculation (i.e., use the previous day's ADG to compute the current day's kg). We believe that generalized models developed by merging different models' concepts might improve our understanding of the relationships of existing variables that were known for their importance but not included in extant models because of the lack of proper information or confidence at that time.

Application of the data envelopment analysis technique to measure the environmental efficiency of the 27 countries of the European Union during the period 2012-2020

In the last decade, we have experienced a changing geopolitical context that has caused changes in the energy context. In addition, human activity contributes to global warming or sea level rising, i.e., climate change. A set of action policies have been implemented to continue fighting against this environmental situation (such as the Paris Agreement, the COP27, or the European Green Deal for 2030); therefore, it is necessary to determine whether we are on the right track. It is compulsory to develop predictive models that accurately analyze the current status and the already path undertaken. To this end, this article analyzes the environmental efficiency of the 27 countries of the European Union (excluding the UK) using the so-called data envelopment analysis (DEA). In particular, economic (GDP and GDP per capita), environmental (CO2 and CH4 emissions), electricity production data, the volume of vehicles, and the industrial production rate of the different countries were collected to calculate environmental efficiency. Once these data were collected, the environmental efficiency was calculated using two methods based on the DEA. The results show that out of the 27 countries, only 12 have a relatively high environmental efficiency, although it could be improved, implementing a set of corrections. However, other countries have a low eco-efficiency performance and they must improve in the coming years. We can highlight that rich countries are closer to achieving high environmental efficiency than less developed countries.

Graphical Abstract

Political map of the European Union indicating the average eco-efficiency with colors of the 27 countries of the DEA method.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10098-023-02553-9.

Research needs for a food system transition

The global food system, and animal agriculture in particular, is a major and growing contributor to climate change, land system change, biodiversity loss, water consumption and contamination, and environmental pollution. The copious production and consumption of animal products are also contributing to increasingly negative public health outcomes, particularly in wealthy and rapidly industrializing countries, and result in the slaughter of trillions of animals each year. These impacts are motivating calls for reduced reliance on animal-based products and increased use of replacement plant-based products. However, our understanding of how the production and consumption of animal products, as well as plant-based alternatives, interact with important dimensions of human and environment systems is incomplete across space and time. This inhibits comprehensively envisioning global and regional food system transitions and planning to manage the costs and synergies thereof. We therefore propose a cross-disciplinary research agenda on future target-based scenarios for food system transformation that has at its core three main activities: (1) data collection and analysis at the intersection of animal agriculture, the environment, and societal well-being, (2) the construction of target-based scenarios for animal products informed by these new data and empirical understandings, and (3) the evaluation of impacts, unintended consequences, co-benefits, and trade-offs of these target-based scenarios to help inform decision-making.

When you wish upon a (GWP) star: Environmental governance and the reflexive performativity of global warming metrics

The metrics used in environmental management are performative. That is, the tools deployed to classify and measure the natural world interact with the things they were designed to observe. The idea of performativity also captures the way these interactions shape or distort the governance activities that metrics are used to inform. The performativity of metrics reveals how mundane practices of measurement and auditing are inscribed with substantial power. This has proven particularly true for the global warming metrics, like GWP100, that are central to the management of anthropogenic climate change. Greenhouse gases are materially heterogenous, and the metrics used to commensurate their various warming impacts influence the distribution of both culpability and capital in climate policy and markets. The publication of a new warming metric, GWP* (or GWP Star), has generated a modest scientific controversy, as a diverse cast of stakeholders recognize this performativity seek to influence the metrological regime under which they live. We analyse this controversy, particularly as it unfolded in the fractious discourse around sustainable food and farming, to develop the concept of reflexive performativity: where actors are anticipatory and strategic in their engagement with the metrics that are used to govern their lives. We situate this idea in relation to, and in tentative evidential support of, the concept of reflexive modernization.

Methane emissions from California dairies estimated using novel climate metric Global Warming Potential Star show improved agreement with modeled warming dynamics

Introduction

Carbon dioxide (CO2) and methane (CH4) are two of the primary greenhouse gases (GHG) responsible for global warming. The “stock gas” CO2 accumulates in the atmosphere even if rates of CO2 emission decline. In contrast, the “flow gas” CH4 has an e-folding time of about 12 years and is removed from the atmosphere in a relatively short period of time. The climate impacts of cumulative pollutants such as CO2 and short-lived climate pollutants (SLCP) such as CH4 are often compared using Global Warming Potential (GWP), a metric that converts non-CO2 GHG into CO2-equivalent emissions. However, GWP has been criticized for overestimating the heating effects of declining SLCP emissions and conversely underestimating the heating impact of increasing SLCP emissions. Accurate quantification of the temperature effects of different CH4 emissions scenarios is particularly important to fully understanding the climate impacts of animal agriculture, whose GHG emissions are dominated by CH4.

Methods

A modified GWP metric known as Global Warming Potential Star (GWP*) has been developed to directly quantify the relationship between SLCP emissions and temperature change, which GWP cannot do. In this California dairy sector case study, we contrasted GWP- versus GWP*-based estimates of historical warming dynamics of enteric and manure CH4 from lactating dairy cattle. We predicted future dairy CH4 emissions under business-as-usual and reduction scenarios and modeled the warming effects of these various emission scenarios.

Results

We found that average CO2 warming equivalent emissions given by GWP* were greater than those given by GWP under increasing annual CH4 emissions rates, but were lower under decreasing CH4 emissions rates. We also found that cumulative CO2 warming equivalent emissions given by GWP* matched modeled warming driven by decreasing CH4 emissions more accurately than those given by GWP.

Discussion

These results suggest that GWP* may provide a more accurate tool for quantifying SLCP emissions in temperature goal and emissions reduction-specific policy contexts.

Deep near-term mitigation of short-lived climate forcers in Oman: grand challenges and prospects

Over time, short-lived climate forcers (SLCFs) have gradually gained prominence as a rationale in the international global mitigation strategy to preserve temperature below 1.5 °C by the end of this century. Scientists cite the short-term gains in air quality and health co-benefits associated with reducing SLCFs as grounds for raising the pressure on governments to eliminate SLCFs rapidly and aggressively. There is little research on whether deep SLCF mitigation during the next decade is feasible in low- and middle-income nations, particularly the hydrocarbon-based economy. This study estimates current and future emissions of potent SLCFs as methane (CH₄) hydrofluorocarbons (HFCs) in Oman using the basic tier 1 approach of the Intergovernmental Panel on Climate Change (IPCC) greenhouse gases (GHG) inventory Guidelines of 2006. Current and future emission of black carbon (BC) was also quantified using specific emission factors. A total of 38,268 Gg of SLFCs were released into the atmosphere in Oman in 2015, accounting for 38.8% of the country's total GHG emissions, and is expected to rise significantly over the next decade to reach 67,777 Gg by 2030. The analysis reveals that the source of Oman's highly potent SLCF emissions is associated with key and critical economic sectors such as the oil and gas industry, heavy road transportation, residential air conditioning (RAC), and industrial refrigeration. These vital economic sectors impose a "Grand Challenge" on the immediate reduction of SLCFs in Oman and the Gulf Cooperation Council (GCC). Accomplishing a rapid, significant reduction in highly potent SLCFs from the three challenging sectors over a 5- to 10-year time period does not appear feasible or realistic in the context of international market mechanisms, socioeconomic factors, and mitigation targets. Achieving a significant reduction in SLCFs for a hydrocarbon-based economy requires a profound economic shift. Creating an effective long-term vision for a post-oil economy over the next two decades provides a sound foundation for implementing economic and societal transformation policies incorporating near-zero-emission measures for the potent SLCFs.

Lowering water table reduces carbon sink strength and carbon stocks in northern peatlands

Peatlands at high latitudes have accumulated >400 Pg carbon (C) because saturated soil and cold temperatures suppress C decomposition. This substantial amount of C in Arctic and Boreal peatlands is potentially subject to increased decomposition if the water table (WT) decreases due to climate change, including permafrost thaw-related drying. Here, we optimize a version of the Organizing Carbon and Hydrology In Dynamic Ecosystems model (ORCHIDEE-PCH4) using site-specific observations to investigate changes in CO₂ and CH₄ fluxes as well as C stock responses to an experimentally manipulated decrease of WT at six northern peatlands. The unmanipulated control peatlands, with the WT <20 cm on average (seasonal max up to 45 cm) below the surface, currently act as C sinks in most years (58 ± 34 g C m^-2  year^-1 ; including 6 ± 7 g C-CH₄ m^-2  year^-1 emission). We found, however, that lowering the WT by 10 cm reduced the CO₂ sink by 13 ± 15 g C m^-2  year^-1 and decreased CH₄ emission by 4 ± 4 g CH₄ m^-2  year^-1 , thus accumulating less C over 100 years (0.2 ± 0.2 kg C m^-2 ). Yet, the reduced emission of CH₄ , which has a larger greenhouse warming potential, resulted in a net decrease in greenhouse gas balance by 310 ± 360 g CO_2-eq  m^-2  year^-1 . Peatlands with the initial WT close to the soil surface were more vulnerable to C loss: Non-permafrost peatlands lost >2 kg C m^-2 over 100 years when WT is lowered by 50 cm, while permafrost peatlands temporally switched from C sinks to sources. These results highlight that reductions in C storage capacity in response to drying of northern peatlands are offset in part by reduced CH₄ emissions, thus slightly reducing the positive carbon climate feedbacks of peatlands under a warmer and drier future climate scenario.

Organics composition and microbial analysis reveal the different roles of biochar and hydrochar in affecting methane oxidation from paddy soil

Biochar and hydrochar, as valuable and eco-friendly soil remediation materials from greenwaste, have potential to enhance methane oxidation in paddy soil. But the mechanism of biomass carbon on the improvement of methane-oxidizing bacteria communities in paddy soil has not been adequately elucidated. In the present study, the effect of different-temperature rice straw-based biomass carbon (RB400, RB600, RH250 and RH300) on methane oxidation were investigated by analyzing the soil dissolved organic matter (DOM), physicochemical properties and changes in microbial community structure. The results of the 17-day incubation experiment showed that the methane oxidation rate increased under all types of biomass carbon in the first 6 days. The enhancement of methane oxidation rate was more pronounced for biochar compared to hydrochar, with RB600 being the most effective treatment. The result of excitation-emission matrix (EEM) fluorescence spectroscopy showed that less DOM were released from the soil in the biochar treatments compared to the hydrochar treatments and protein-like were detected only in the hydrochar group. Microbial analysis further showed that hydrochar inhibited the growth of Bacillus, Methylobacter, and Methylocystis, while RB600 significantly increased the relative abundance of methanotrophs (responsible for methane oxidation), such as Methylocystis and Methylobacter, which was consistent with their different effects on the methane oxidation rate. Moreover, from the analysis of principal component analysis (PCA) and canonical correspondence analysis (CCA), Methylobacter and Methylocystis were negatively respond to H/C of biomass carbon. The present study provides a deeper understanding of the effect of biomass carbon obtained by different processes on methane oxidation when applied to soil from the perspective of organic matter and microbial communities.

Can Restoration of Freshwater Mineral Soil Wetlands Deliver Nature-Based Climate Solutions to Agricultural Landscapes?

This study advances scientific understanding of the magnitude of carbon sequestration that could be achieved through conservation (securing existing carbon stocks) and restoration (creating new carbon stocks) of freshwater mineral soil wetlands on agricultural landscapes. Within an agricultural landscape in southern Ontario (Canada), 65,261 wetlands comprising 63,135 ha were lost. Of these, 6,899 wetlands comprising 5,198 ha were “easy-to-restore” wetlands, defined as wetlands that were small (&lt;0.5 ha), with no hydrological inflow or outflow, and that were drained by a drainage ditch and could be restored by plugging the drainage ditch. Within these easy-to-restore wetlands, a chronosequence of wetlands that covered a range of restoration ages [i.e., drained (0 years), 15 years, 25 years, 40 years, and intact marshes] was established to capture potential changes in rates of sedimentation and organic carbon (OC) sequestration with restoration age. Three sediment cores were collected at the center of the open-water portion of the wetland and segmented in the field. In the lab, each individual segment from each core was dried, sieved through a 2-mm mesh, weighed and analyzed for 137Cs and 210Pb radioisotopes and OC. OC stocks (35.60 Mg ha–1) and OC sequestration rates (0.89 Mg C ha–2 yr–1) in wetlands restored for 40 years were comparable to if not marginally larger than intact wetlands, suggesting that restoration promotes OC sequestration but that an initial recovery phase of up to 25 years or more is needed before returning to a pre-drainage equilibrium. An economic analysis to compare the costs and benefits of wetland conservation and restoration was then conducted. The benefit-cost analysis revealed that the financial benefits of carbon sequestration are greater than the financial costs over a 30-year time horizon for retaining wetlands but not for restoring wetlands. The breakeven costs such that wetland restoration is economically feasible based on current carbon price projections is estimated to be $17,173 CAD ha–1 over the 30-year time horizon; any wetland restoration project that costs this amount or less could be justified on economic grounds based solely on the carbon benefits. This study’s findings indicate that wetlands are important nature-based climate solutions, but that incentivizing their use through a carbon market will require either scientific innovations to reduce restoration costs or increase carbon sequestration rates, or stacking carbon benefits with other ecosystem service benefits into a comprehensive market for nature-based climate solutions.

Aircraft Emissions, Their Plume-Scale Effects, and the Spatio-Temporal Sensitivity of the Atmospheric Response: A Review

Non-CO2 aircraft emissions are responsible for the majority of aviation’s climate impact, however their precise effect is largely dependent on the environmental conditions of the ambient air in which they are released. Investigating the principal causes of this spatio-temporal sensitivity can bolster understanding of aviation-induced climate change, as well as offer potential mitigation solutions that can be implemented in the interim to low carbon flight regimes. This review paper covers the generation of emissions and their characteristic dispersion, air traffic distribution, local and global climate impact, and operational mitigation solutions, all aimed at improving scientific awareness of aviation’s non-CO2 climate impact.

The Impact of Environmental Taxes on the Level of Greenhouse Gas Emissions in Poland and Sweden

The research presented in the article was aimed at verifying the effectiveness of environmental taxes in reducing the level of greenhouse gas emissions. For this purpose, data provided by Eurostat in the environmental taxes category were used. They were treated as explanatory variables. Data were entered into the ARMAX models built by the authors. The dependent variable was the emission of two greenhouse gases covered by the research, namely carbon dioxide and methane. The research was carried out in Poland, for which the results obtained for Sweden were used as the benchmark. The built models made it possible to verify the relationship between environmental taxes in the categories of energy, transport, pollution, resources, and the level of CO2 and CH4 emissions. The nature of the explanatory variable was also examined. Environmental taxes can fulfill a fiscal, incentive, and redistributive function. The conducted research shows that these taxes, in fact, fulfill mainly a fiscal function, while redistributive and incentive functions are insufficient. It was also observed that the direction and strength of the impact of taxes differ depending on the greenhouse gas.

Responsible agriculture must adapt to the wetland character of mid-latitude peatlands

Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yr^-1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Reducing drainage depths is, therefore, essential for responsible peatland management. Peatland restoration can substantially reduce emissions. However, this may conflict with societal needs to maintain productive use, to protect food security and livelihoods. Wetland agriculture strategies will, therefore, be required to adapt agriculture to the wetland character of peatlands, and balance GHG mitigation against productivity, where halting emissions is not immediately possible. Paludiculture may substantially reduce GHG emissions but will not always be viable in the current economic landscape. Reduced drainage intensity systems may deliver partial reductions in the rate of emissions, with smaller modifications to existing systems. These compromise systems may face fewer hurdles to adoption and minimize environmental harm until societal conditions favour strategies that can halt emissions. Wetland agriculture will face agronomic, socio-economic and water management challenges, and careful implementation will be required. Diversity of values and priorities among stakeholders creates the potential for conflict. Successful implementation will require participatory research approaches and co-creation of workable solutions. Policymakers, private sector funders and researchers have key roles to play but adoption risks would fall predominantly on land managers. Development of a robust wetland agriculture paradigm is essential to deliver resilient production systems and wider environmental benefits. The challenge of responsible use presents an opportunity to rethink peatland management and create thriving, innovative and green wetland landscapes for everyone's future benefit, while making a vital contribution to global climate change mitigation.

Animal board invited review: Animal source foods in healthy, sustainable, and ethical diets - An argument against drastic limitation of livestock in the food system

Animal source foods are evolutionarily appropriate foods for humans. It is therefore remarkable that they are now presented by some as unhealthy, unsustainable, and unethical, particularly in the urban West. The benefits of consuming them are nonetheless substantial, as they offer a wide spectrum of nutrients that are needed for cell and tissue development, function, and survival. They play a role in proper physical and cognitive development of infants, children, and adolescents, and help promote maintenance of physical function with ageing. While high-red meat consumption in the West is associated with several forms of chronic disease, these associations remain uncertain in other cultural contexts or when consumption is part of wholesome diets. Besides health concerns, there is also widespread anxiety about the environmental impacts of animal source foods. Although several production methods are detrimental (intensive cropping for feed, overgrazing, deforestation, water pollution, etc.) and require substantial mitigation, damaging impacts are not intrinsic to animal husbandry. When well-managed, livestock farming contributes to ecosystem management and soil health, while delivering high-quality foodstuffs through the upcycling of resources that are otherwise non-suitable for food production, making use of marginal land and inedible materials (forage, by-products, etc.), integrating livestock and crop farming where possible has the potential to benefit plant food production through enhanced nutrient recycling, while minimising external input needs such as fertilisers and pesticides. Moreover, the impacts on land use, water wastage, and greenhouse gas emissions are highly contextual, and their estimation is often erroneous due to a reductionist use of metrics. Similarly, whether animal husbandry is ethical or not depends on practical specificities, not on the fact that animals are involved. Such discussions also need to factor in that animal husbandry plays an important role in culture, societal well-being, food security, and the provision of livelihoods. We seize this opportunity to argue for less preconceived assumptions about alleged effects of animal source foods on the health of the planet and the humans and animals involved, for less top-down planning based on isolated metrics or (Western) technocratic perspectives, and for more holistic and circumstantial approaches to the food system.

Methane and the Paris Agreement temperature goals

Meeting the Paris Agreement temperature goal necessitates limiting methane (CH4)-induced warming, in addition to achieving net-zero or (net-negative) carbon dioxide (CO2) emissions. In our model, for the median 1.5°C scenario between 2020 and 2050, CH4 mitigation lowers temperatures by 0.1°C; CO2 increases it by 0.2°C. CO2 emissions continue increasing global mean temperature until net-zero emissions are reached, with potential for lowering temperatures with net-negative emissions. By contrast, reducing CH4 emissions starts to reverse CH4-induced warming within a few decades. These differences are hidden when framing climate mitigation using annual 'CO2-equivalent' emissions, including targets based on aggregated annual emission rates. We show how the different warming responses to CO2 and CH4 emissions can be accurately aggregated to estimate warming by using 'warming-equivalent emissions', which provide a transparent and convenient method to inform policies and measures for mitigation, or demonstrate progress towards a temperature goal. The method presented (GWP*) uses well-established climate science concepts to relate GWP100 to temperature, as a simple proxy for a climate model. The use of warming-equivalent emissions for nationally determined contributions and long-term strategies would enhance the transparency of stocktakes of progress towards a long-term temperature goal, compared to the use of standard equivalence methods. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Dynamic Life Cycle Assessment of Energy Technologies under Different Greenhouse Gas Concentration Pathways

Global warming potential (GWP) has been widely used in the life cycle assessment (LCA) to quantify the climate impacts of energy technologies. Most LCAs are static analyses without considering the dynamics of greenhouse gas (GHG) emissions and changes in background GHG concentrations. This study presents a dynamic approach to analyze the life-cycle GWP of energy technologies in different timeframes and representative GHG concentration pathways. Results show that higher atmospheric GHG concentrations lead to higher life-cycle GWP for long-term analysis. The impacts of background GHG concentrations are more significant for technologies with large operational emissions or CH₄ emissions than technologies with low operational emissions. The case study for the U.S. electricity sector in 2020-2050 shows the impacts of background GHG concentrations and different LCA methods on estimating national climate impacts of different energy technology scenarios. Based on the results, it is recommended for future LCAs to incorporate temporal effects of GHG emissions when (1) the technology has large operational GHG emissions or CH₄ emissions; (2) the analysis time frame is longer than 50 years; (3) when LCA results are used for policymaking or technology comparisons for mitigating climate change.

The adsorption behaviors of N2O on penta-graphene and Ni-doped penta-graphene

In order to develop the adsorption application of penta-graphene (PG) to N₂O gas molecule, we calculated the sensing properties of PG and Ni-doped PG to N₂O molecule via first-principles calculations. Based on the calculated adsorption energy, charge transfer, band gap, density of states and partial density of states, we observed that this gas molecule was weakly physically adsorbed on the surface of intrinsic PG, while the adsorption behaviors on the surface of Ni-doped PG were greatly influenced by the doping sites and adsorption orientations. With the Ni atom doped at the sp² hybridized carbon site, strong chemical adsorption between the gas molecule and the substrate was induced. The adsorption structure of the N₂O molecule with its N atom close to the substrate exhibited better stability. Moreover, an external perpendicular electric field could enhance the adsorption performance of the N₂O molecule and adjust the charge transfer between the molecule and substrate. Our results broaden the adsorption applications of PG and indicate that Ni-doped PG is a potential candidate for N₂O gas sensors.

N₂O molecule is chemically adsorbed on the surface of Ni-doped penta-graphene only when the Ni atom is doped at the sp² hybridized carbon site. External perpendicular electric field can enhance the adsorption performance.

Voisin Rational Grazing as a Sustainable Alternative for Livestock Production

Current livestock practices do not meet current real-world social and environmental requirements, pushing farmers away from rural areas and only sustaining high productivity through the overuse of fossil fuels, causing numerous environmental side effects. In this narrative review, we explore how the Voisin Rational Grazing (VRG) system responds to this problem. VRG is an agroecological system based on four principles that maximise pasture growth and ruminant intake, while, at the same time, maintaining system sustainability. It applies a wide range of regenerative agricultural practices, such as the use of multispecies swards combined with agroforestry. Planning allows grazing to take place when pastures reach their optimal resting period, thus promoting vigorous pasture regrowth. Moreover, paddocks are designed in a way that allow animals to have free access to water and shade, improving overall animal welfare. In combination, these practices result in increased soil C uptake and soil health, boost water retention, and protect water quality. VRG may be used to provide ecosystem services that mitigate some of the current global challenges and create opportunities for farmers to apply greener practices and become more resilient. It can be said that VRG practitioners are part of the initiatives that are rethinking modern livestock agriculture. Its main challenges, however, arise from social constraints. More specifically, local incentives and initiatives that encourage farmers to take an interest in the ecological processes involved in livestock farming are still lacking. Little research has been conducted to validate the empirical evidence of VRG benefits on animal performance or to overcome VRG limitations.

Short- and long-term warming effects of methane may affect the cost-effectiveness of mitigation policies and benefits of low-meat diets

Methane’s short atmospheric life has important implications for the design of global climate change mitigation policies in agriculture. Three different agricultural economic models are used to explore how short- and long-term warming effects of methane can affect the cost-effectiveness of mitigation policies and dietary transitions. Results show that the choice of a particular metric for methane’s warming potential is key to determine optimal mitigation options, with metrics based on shorter-term impacts leading to greater overall emission reduction. Also, the promotion of low-meat diets is more effective at reducing greenhouse gas emissions compared to carbon pricing when mitigation policies are based on metrics that reflect methane’s long-term behaviour. A combination of stringent mitigation measures and dietary changes could achieve substantial emission reduction levels, helping reverse the contribution of agriculture to global warming.

Examining the Environmental Impacts of the Dairy and Baby Food Industries: Are First-Food Systems a Crucial Missing Part of the Healthy and Sustainable Food Systems Agenda Now Underway?

Food systems are increasingly being understood as driving various health and ecological crises and their transformation is recognised as a key opportunity for planetary health. First-food systems represent an underexplored aspect of this transformation. Despite breastfeeding representing the optimal source of infant nutrition, use of commercial milk formula (CMF) is high and growing rapidly. In this review, we examine the impact of CMF use on planetary health, considering in particular its effects on climate change, water use and pollution and the consequences of these effects for human health. Milk is the main ingredient in the production of CMF, making the role of the dairy sector a key area of attention. We find that CMF use has twice the carbon footprint of breastfeeding, while 1 kg of CMF has a blue water footprint of 699 L; CMF has a significant and harmful environmental impact. Facilitation and protection of breastfeeding represents a key part of developing sustainable first-food systems and has huge potential benefits for maternal and child health.

Agricultural methane emissions and the potential formitigation

Agriculture is the largest anthropogenic source of methane (CH₄), emitting 145 Tg CH₄y^-1 to the atmosphere in 2017. The main sources are enteric fermentation, manure management, rice cultivation and residue burning. There is significant potential to reduce CH₄ from these sources, with bottom-up mitigation potentials of approximately 10.6, 10, 2 and 1 Tg CH₄y^-1 from rice management, enteric fermentation, manure management and residue burning. Other system-wide studies have assumed even higher potentials of 4.8-47.2 Tg CH₄y^-1 from reduced enteric fermentation, and 4-36 Tg CH₄y^-1 from improved rice management. Biogas (a methane-rich gas mixture generated from the anaerobic decomposition of organic matter and used for energy) also has the potential to reduce unabated CH₄ emissions from animal manures and human waste. In addition to these supply side measures, interventions on the demand-side (shift to a plant-based diet and a reduction in total food loss and waste by 2050) would also significantly reduce methane emissions, perhaps in the order of greater than 50 Tg CH₄y^-1. While there is a pressing need to reduce emissions of long-lived greenhouse gases (CO₂ and N₂O) due to their persistence in the atmosphere, despite CH₄ being a short-lived greenhouse gas, the urgency of reducing warming means we must reduce any GHG emissions we can as soon as possible. Because of this, mitigation actions should focus on reducing emissions of all the three main anthropogenic greenhouse gases, including CH₄. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part1)'.

How necessary and feasible are reductions of methane emissions from livestock to support stringent temperature goals?

Agriculture is the largest single source of global anthropogenic methane (CH4) emissions, with ruminants the dominant contributor. Livestock CH4 emissions are projected to grow another 30% by 2050 under current policies, yet few countries have set targets or are implementing policies to reduce emissions in absolute terms. The reason for this limited ambition may be linked not only to the underpinning role of livestock for nutrition and livelihoods in many countries but also diverging perspectives on the importance of mitigating these emissions, given the short atmospheric lifetime of CH4. Here, we show that in mitigation pathways that limit warming to 1.5°C, which include cost-effective reductions from all emission sources, the contribution of future livestock CH4 emissions to global warming in 2050 is about one-third of that from future net carbon dioxide emissions. Future livestock CH4 emissions, therefore, significantly constrain the remaining carbon budget and the ability to meet stringent temperature limits. We review options to address livestock CH4 emissions through more efficient production, technological advances and demand-side changes, and their interactions with land-based carbon sequestration. We conclude that bringing livestock into mainstream mitigation policies, while recognizing their unique social, cultural and economic roles, would make an important contribution towards reaching the temperature goal of the Paris Agreement and is vital for a limit of 1.5°C. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Path to net zero is critical to climate outcome

Net zero greenhouse gas targets have become a central element for climate action. However, most company and government pledges focus on the year that net zero is reached, with limited awareness of how critical the emissions pathway is in determining the climate outcome in both the near- and long-term. Here we show that different pathways of carbon dioxide and methane—the most prominent long-lived and short-lived greenhouse gases, respectively—can lead to nearly 0.4 °C of warming difference in midcentury and potential overshoot of the 2 °C target, even if they technically reach global net zero greenhouse gas emissions in 2050. While all paths achieve the Paris Agreement temperature goals in the long-term, there is still a 0.2 °C difference by end-of-century. We find that early action to reduce both emissions of carbon dioxide and methane simultaneously leads to the best climate outcomes over all timescales. We therefore recommend that companies and countries supplement net zero targets with a two-basket set of interim milestones to ensure that early action is taken for both carbon dioxide and methane. A one-basket approach, such as the standard format for Nationally Determined Contributions, is not sufficient because it can lead to a delay in methane mitigation.

Modeling the effects of steroid implant use on the environmental and economic sustainability of Brazilian beef production

Brazilian beef systems contribute 14.9% of global beef production, therefore given climate change concerns, there is a clear need to reduce environmental impacts while maintaining economic viability. This study evaluated the hypothesis that steroid implant use in Brazilian beef cattle would reduce resource use, greenhouse gas (GHG) emissions and economic costs of production, thereby improving environmental and economic sustainability. A deterministic model based on beef cattle population demographics, nutrition and performance was used to quantify resource inputs and GHG emissions per 1.0 × 106 kg of hot carcass weight (HCW) beef. System boundaries extended from cropping input manufacture to cattle arriving at the slaughterhouse. Beef systems were modeled using herd population dynamics, feed and performance data sourced from producers in four Brazilian states, with additional data from global databases. Implants were used in calves, growing and finishing cattle at low (LI), medium (MI), and high (HI) levels of performance enhancement, compared to nonimplanted (NI) controls. Feed use results were used in combination with producer-derived input costs to assess the economic impacts of implant use, including production costs and returns on investment. Improved FCE, ADG, and carcass weights conferred by implant use reduced the number of cattle and the time taken to produce 1.0 × 106 kg HCW beef. Compared to NI controls, the quantities of feed, land, water and fossil fuels required to produce 1.0 × 106 kg HCW beef was reduced in implanted cattle, with reductions proportional to the performance-enhancing effect of the implant (HI > MI > LI). Implant use reduced GHG emissions per 1.0 × 106 kg HCW beef by 9.4% (LI), 12.6% (MI), or 15.8% (HI). Scaling up the MI effects to represent all eligible Brazilian cattle being implanted, revealed avoided GHG emissions equivalent to the annual exhaust emissions of 62.0 × 106 cars. Economic impacts of implant use reflected the environmental results, resulting in a greater margin for the producers within each system (cow-calf through to finishing). The 6.13% increase in kg of HCW beef produced generates a cost reduction of 3.76% and an increase in the return on invested capital of 4.14% on average. Implants offer the opportunity for Brazilian beef producers to demonstrate their dedication to improving environmental and economic sustainability through improved productivity, although care must be taken to avoid negative trade-offs.

Animal board invited review: Animal agriculture and alternative meats - learning from past science communication failures

Sustainability discussions bring in multiple competing goals, and the outcomes are often conflicting depending upon which goal is being given credence. The role of livestock in supporting human well-being is especially contentious in discourses around sustainable diets. There is considerable variation in which environmental metrics are measured when describing sustainable diets, although some estimate of the greenhouse gas (GHG) emissions of different diets based on varying assumptions is commonplace. A market for animal-free and manufactured food items to substitute for animal source food (ASF) has emerged, driven by the high GHG emissions of ASF. Ingredients sourced from plants, and animal cells grown in culture are two approaches employed to produce alternative meats. These can be complemented with ingredients produced using synthetic biology. Alternative meat companies promise to reduce GHG, the land and water used for food production, and reduce or eliminate animal agriculture. Some CEOs have even claimed alternative meats will 'end world hunger'. Rarely do such self-proclamations emanate from scientists, but rather from companies in their efforts to attract venture capital investment and market share. Such declarations are reminiscent of the early days of the biotechnology industry. At that time, special interest groups employed fear-based tactics to effectively turn public opinion against the use of genetic engineering to introduce sustainability traits, like disease resistance and nutrient fortification, into global genetic improvement programs. These same groups have recently turned their sights on the 'unnaturalness' and use of synthetic biology in the production of meat alternatives, leaving agriculturists in a quandary. Much of the rationale behind alternative meats invokes a simplistic narrative, with a primary focus on GHG emissions, ignoring the nutritional attributes and dietary importance of ASF, and livelihoods that are supported by grazing ruminant production systems. Diets with low GHG emissions are often described as sustainable, even though the nutritional, social and economic pillars of sustainability are not considered. Nutritionists, geneticists, and veterinarians have been extremely successful at developing new technologies to reduce the environmental footprint of ASF. Further technological developments are going to be requisite to continuously improve the efficiency of animal source, plant source, and cultured meat production. Perhaps there is an opportunity to collectively communicate how innovations are enabling both alternative- and conventional-meat producers to more sustainably meet future demand. This could counteract the possibility that special interest groups who promulgate misinformation, fear and uncertainty, will hinder the adoption of technological innovations to the ultimate detriment of global food security.

Ensuring that offsets and other internationally transferred mitigation outcomes contribute effectively to limiting global warming

Ensuring the environmental integrity of internationally transferred mitigation outcomes, whether through offset arrangements, a market mechanism or non-market approaches, is a priority for the implementation of Article 6 of the Paris Agreement. Any conventional transferred mitigation outcome, such as an offset agreement, that involves exchanging greenhouse gases with different lifetimes can increase global warming on some timescales. We show that a simple 'do no harm' principle regarding the choice of metrics to use in such transactions can be used to guard against this, noting that it may also be applicable in other contexts such as voluntary and compliance carbon markets. We also show that both approximate and exact 'warming equivalent' exchanges are possible, but present challenges of implementation in any conventional market. Warming-equivalent emissions may, however, be useful in formulating warming budgets in a two-basket approach to mitigation and in reporting contributions to warming in the context of the global stocktake.

Simulation and evaluation of sustainable climate trajectories for aviation

In 2019, aviation was responsible for 2.6% of world CO2 emissions as well as additional climate impacts such as contrails. Like all industrial sectors, the aviation sector must implement measures to reduce its climate impact. This paper focuses on the simulation and evaluation of climate scenarios for air transport. For this purpose, a specific tool (CAST for "Climate and Aviation - Sustainable Trajectories") has been developed at ISAE-SUPAERO. This tool follows a methodology for the assessment of climate impacts adapted to aviation. Firstly, models for the main levers of action, such as air traffic, aircraft energy consumption and energy decarbonization, are provided using trend projections from historical data or assumptions from the literature. Second, the evaluation of scenarios is based on aviation carbon budgets, which are also extended to non-CO2 effects using the concept of GWP*. Several scenario analyses are performed in this paper using CAST allowing different conclusions to be drawn. For instance, the modelling of the scenarios based on the more recent ATAG (Air Transport Action Group) commitments shows that aviation would consume 6.5% of the world carbon budget for +1.5 °C. Some illustrative scenarios are also proposed. By allocating 2.6% of the world carbon budget to aviation, it is shown that air transport is compatible with a +2 °C trajectory when the annual growth rate of air traffic varies between -1.8% and +2.9%, depending on the technological improvements considered. However, using the same methodology for a +1.5 °C trajectory shows that a drastic decrease in air traffic is necessary. Lastly, analyses including non-CO2 effects emphasize the importance of implementing specific strategies for mitigating contrails.

Environmental impact of primary beef production chain in Colombia: Carbon footprint, non-renewable energy and land use using Life Cycle Assessment

In Colombia, the beef production chain accounts for approximately 11.6 million cattle heads and annually produces 933 million kg of the beef carcass. There are no life cycle assessment (LCA) studies that have evaluated the environmental performance of Colombian beef systems. The present study aimed to estimate the carbon footprint (CF), non-renewable energy use, and land use of 251 cow-calf and 275 fattening farms in Colombia. The study also aimed to identify the main hotspots of adverse environmental impacts and propose possible mitigation options and their cost-effectiveness. The impact categories were estimated using the 2006 IPCC and the 2019 Refinement to 2006 IPCC guidelines, databases, and locally estimated emission factors. The functional units used were 1 kg fat and protein corrected milk (FPCM) and 1 kg live weight gain (LWG), leaving the farm gate. Three methods of allocating environmental burdens to meat and milk products were applied: economic, energy, and mass allocation. The adoption of improved pastures was considered a mitigation measure, and an economic assessment was performed to estimate the relative cost-effectiveness of its establishment. A principal component multivariate analysis and a Hierarchical Clustering on Principal Components were performed. The economic allocation method assigned a greater environmental burden to meat (83%), followed by energy content (80%) and mass production (73%). The largest sources of GHG emissions were enteric fermentation and manure deposited on pasture. Both cow-calf and fattening systems had a cluster of farms with better productivity, pasture and cattle management practices, and environmental performance. The CF for meat could be reduced by 33 to 56% for cow-calf and 21 to 25% for fattening farms, by adopting improved pastures. Therefore, our results suggest that GHG emissions can be reduced by adopting improved pastures, better agricultural management practices, efficient fertilizer usage, using the optimal stocking rate, and increasing productivity.