Climatic and atmospheric conditions impact mental health, including increased incidents of depression associated with air pollution. A growing body of research considers time-bound ‘snap-shots’ of climatic drivers and mental health outcomes. Less is known about the likely effects of future climate change on mental health. Research is often inhibited by data scarcity, the challenge of synthesising data across multiple geospatial and temporal scales, and the under-representation of hard-to-reach groups. Thus, research methods are needed to integrate and analyse complex environmental and mental health multi-datasets while improving the visibility of under-represented groups. In this methods paper we present a novel approach for investigating the impact of climate change on mental health and addressing some challenges with, a) invisibility of vulnerable groups, and b) integrating complex environmental and mental health multi-datasets. The research aim is to pilot a web-based and smartphone application (Methane Early Warning Network (ME-NET)) for investigating the role of methane as a precursor of on-ground ozone, and the impact of ozone on mental health outcomes to improve civic knowledge and health-protection behaviour in the United Kingdom and Ghana. The methods include exploring the feasibility of using machine learning to develop an ozone early warning system and application co-design.

Ruminal microbes catabolise feed carbohydrates mainly into SCFA, methane (CH4), and carbon dioxide (CO2), with predictable relationships between fermentation end products and net microbial increase. We used a closed in vitro batch culture system, incubating grass and maize silages, and measured total gas production at 8 and 24 h, as well as the truly degraded substrate, the net production of SCFA, CH4, and microbial biomass at 24 h, and investigated the impact of silage type and inoculum microbial mass on fermentation direction. Net microbial yield was negatively correlated with total gas at 8 h (P < 0•001), but not at 24 h (P = 0•052), and negatively correlated with CH4 production (P < 0•001). Higher initial inoculum microbial mass was related to a lower net microbial yield (P < 0•001) but a higher CH4 production (P < 0•001). A significant difference between grass silage and maize silage was detected within the context of these relationships (P < 0•050). The metabolic hydrogen (2H) recovery was 102.8 ± 12.3 % for grass silages and 118.8 ± 13.3% for maize silages. Overall, grass silages favoured more substrate conversion to microbial biomass and less to fermentation end products than maize silage. Lower inoculum microbial mass facilitated more microbial growth and, because of the 2H sink by microbial synthesis, decreased CH4 production.

Methane solubilities at 25°C were measured at 350, 550, and 750 psia in dilute (< 11 wt. %) clay slurries of Na-montmorillonites and argillaceous sediment. Methane solubilities were not significantly affected by the presence of clay. Water hydrated onto the external clay surfaces did not appear to exclude methane. In addition there was no detectable sorption of methane onto the clays. The measured solubilities are consistent with an open structure of the water hydrated onto the clay surface for which the partial molal volume is larger than that of normal water. The results imply that aqueous methane solubilities measured in the laboratory can be used to determine degrees of methane saturation in interstitial solutions in unconsolidated sediments.

Freshwater ecosystems are responsible for a large proportion of global methane emissions to the atmosphere. The radiocarbon (14C) content of this aquatic methane is useful for determining the age and source of this important greenhouse gas. Several methods already exist for the collection of aquatic methane for radiocarbon analysis, but they tend to only sample over short periods of time, which can make them unsuitable for characterizing aquatic methane over longer timespans, and vulnerable to missing short-term events. Here, we describe a new time-integrated method for the collection of aquatic methane that provides samples suitable for radiocarbon analysis, that are representative for periods of up to at least 16 days. We report the results of a suite of tests undertaken to verify the reliability of the method, and the 14C age of aquatic methane from field trials undertaken at sites within Scotland, UK. We believe that this new method provides researchers with a simple approach that is easily deployable and can be used to collect representative time-integrated samples of methane for radiocarbon analysis from a wide range of aquatic environments.

Recent research has shown the potential of speleothem δ13C to record a range of environmental processes. Here, we report on 230Th-dated stalagmite δ13C records for southwest Sulawesi, Indonesia, over the last 40,000 yr to investigate the relationship between tropical vegetation productivity and atmospheric methane concentrations. We demonstrate that the Sulawesi stalagmite δ13C record is driven by changes in vegetation productivity and soil respiration and explore the link between soil respiration and tropical methane emissions using HadCM3 and the Sheffield Dynamic Global Vegetation Model. The model indicates that changes in soil respiration are primarily driven by changes in temperature and CO2, in line with our interpretation of stalagmite δ13C. In turn, modelled methane emissions are driven by soil respiration, providing a mechanism that links methane to stalagmite δ13C. This relationship is particularly strong during the last glaciation, indicating a key role for the tropics in controlling atmospheric methane when emissions from high-latitude boreal wetlands were suppressed. With further investigation, the link between δ13C in stalagmites and tropical methane could provide a low-latitude proxy complementary to polar ice core records to improve our understanding of the glacial–interglacial methane budget.

CH4 is the second most important anthropogenic greenhouse gas and originates from different sources. The use of radiocarbon (14C) analysis of CH4 opens up the possibility to differentiate geological and agricultural origin. At the CologneAMS facility, the demand for 14C analysis of CH4 required the development of a sample handling routine and a vacuum system that converts CH4 to CO2 for direct injection of CO2 into the AMS. We evaluated the processing of CH4 using several series of gas mixtures of 14C-free and modern standards as well as biogas with sample sizes ranging from 10 to 50 µg C. The results revealed a CH4 to CO2 conversion efficiency of 94–97% and blank values comparable to blank values achieved with our routinely used vacuum system for processing CO2 samples. The tests with a near modern CH4:CO2 biogas mixture gave reproducible results with a near modern 14C content of 0.967–1.000 F14C, after applying the background correction.

The experiments reported in this research paper address the effects of replacing ground corn (GC) with full-fat corn germ (FFCG) on nutrient intake and digestibility, nitrogen utilization efficiency, performance, and predicted methane production in dairy cows fed cactus cladodes and sugarcane. We hypothesized that the inclusion of FFCG in the diet would not alter the performance of lactating cows but would reduce the predicted methane production in vivo. Ten multiparous Holstein cows at 90 ± 10 d of lactation and yielding 24.2 ± 3.5 kg milk/d were assigned to dietary treatments consisting of different levels of replacement of GC by FFCG (0; 25; 50; 75 and 100% of diet dry matter) in a replicated 5 × 5 Latin square design with 21-d periods. Methane production was predicted using an automated gas in vitro production system. Except for ether extract intake, which increased, the intake of all nutrients decreased linearly with the replacement of GC by FFCG. The digestibility of dry matter, organic matter and neutral detergent fiber reduced, whereas the digestibility of ether extract increased linearly with FFCG. There were no changes in the digestibility of crude protein. The nitrogen intake and daily excretion in urine and feces decreased, while nitrogen use efficiency increased linearly. There was no significant effect of diets on nitrogen balance or microbial protein synthesis and efficiency. The yield of protein, lactose and total solids in milk showed a quadratic behavior. On the other hand, milk fat yield and energy-corrected milk yield decreased linearly with the replacement of GC by FFCG. No effect on pH or ammonia nitrogen was observed. The production of methane (CH4, g/kg DM) and total CH4 (g/d), and CH4 intensity decreased linearly with the replacement of GC by FFCG. In conclusion, FFCG has been shown to be an effective source of fat to reduce methane production in dairy cows, partially supporting our initial hypothesis. However, as it decreases milk fat production, it is not recommended to replace more than 50% of GC by FFCG for lactating cows fed cactus cladodes and sugarcane.

Medicinal plants with high phytochemical values are critical for enhancing the productivity of livestock systems, while reducing their environmental impact. This study investigated the influence of graded levels of Cassia fistula leaf powder (CFLP) on in vitro ruminal fermentation parameters, gas production and degradability of diets for ruminants. Five concentrate diets were formulated to contain varying levels of CFLP (0, 15, 30, 45 and 60 mg/g dry matter (DM), denoted CF0, CF15, CF30, CF45 and CF60, respectively). The concentrate diets combined with guinea grass hay at the ratio of 4 : 6 (concentrate : forage) served as a substrate for the study. In vitro gas production test was performed by incubating 200 mg DM of the substrate for 48 h. At the end of the incubation period, the total gas and methane production, nutrient digestibility, in vitro fermentation and post-incubation parameters were evaluated. Results revealed a linear decrease (P < 0.001) in gas and methane production across the treatment groups with an increase in CFLP levels. The amount of methane produced varied from 9.3 ml/200 mg DM in the CF60 diet to 20 ml/200 mg DM in the control diet. Nutrient digestibility was highest in the control diet and lowest in the CF60 diet. There was a linear decrease in ammonia-nitrogen and total volatile fatty acid (TVFA) concentration with an increase in the CFLP level. Inclusion of CFLP up to 30 mg/g DM ruminant diet was found to reduce methane production and ammonia-nitrogen concentration with minimal effects on nutrient degradation and TVFA concentration.

An on-farm field experiment was conducted in northeastern Thailand to assess the effects of different eucalyptus biochar (BC) application rates, in combination with mineral fertilizers, on upland rice and a succeeding crop of sugarcane on sandy soil. Soil mineral N and greenhouse gas emissions were also evaluated. The field experiment consisted of three treatments: no biochar (BC0), 3.1 Mg ha−1 of biochar (BC1), and 6.2 Mg ha−1 of biochar (BC2). All treatments received the same recommended fertilizer rate. Soil mineral N, and emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored after BC application. The results revealed that the BC2 treatment caused lower soil mineral N content than that of the BC0 treatment during the upland rice period. During the sugarcane period, the BC2 treatment induced a greater soil mineral N content than the BC1 treatment but had no significant difference from the BC0 treatment. The BC2 treatment resulted in significantly lower cumulative CH4 and N2O emissions than the BC0 treatment during the upland rice period. In conclusion, we found that the BC2 treatment alleviated the global warming potential from CH4 and N2O emissions throughout the experiment, causing slight changes in soil N availability in the upland rice–sugarcane cropping system.

The paper by K. L. Blaxter and J. L. Clapperton (1965) ‘Prediction of the amount of methane produced by ruminants. Br J Nutr 19, 511–522’ has been cited 656 times according to Web of Science and continues to be cited with increasing frequency to the present day. The analysis described in the paper, or meta-analysis as it would be known now, is of methane production from cattle and sheep based on forty-eight trials using closed-circuit respiration chambers, all carried out at the Hannah Research Institute, Ayr, UK, between 1955 and 1965. Methane emissions per unit of diet fed were shown to vary depending on diet, level of feeding and individual animal. As such, previous notions that methane emissions were essentially proportional to energy intake were set aside. The main reasons for the paper’s continuing citation are the set of equations that can be used to predict methane emissions from ruminants when the technically demanding respiration chambers are unavailable, and that it was the first definitive study to describe the complexities of methane emissions with respect to animals and diets. The paper thus provided abundant insights of the relations between ruminant methane emissions and nutritional biology, and rumen microbiology, in particular, that have informed countless research projects in the intervening half-century. Given the importance of methane as a greenhouse gas in the climate change scenario, these insights are at least as relevant today as they were in 1965.

This study examines the effect of cereal and livestock production-induced greenhouse gas emissions (GHGs) across high-, middle- and low-income countries from 2002 to 2016. A structural equation formulated within an environmental modeling framework is tested using the balanced panel-corrected standard errors estimation procedure. The findings showed that total food production is strongly correlated with methane and nitrous oxide in high-income countries and nitrous oxide emissions in middle-income countries. After disaggregating total food production into cereal and livestock production, the findings revealed that cereal production is positively and statistically significantly correlated with nitrous oxide emissions in high- and middle-income countries. The findings also confirmed that livestock production is positively and statistically significantly correlated with methane and nitrous oxide emissions in high-income countries. Incomes, industrial expansion, forest cover and education are other strong common determinants of GHGs in all three income categories of countries. The prime policy implication of this finding is the need for the food producers to transit toward environmentally cleaner and sustainable food production systems that mitigate GHGs and improve environmental performance and comply with the broader objectives of the United Nations Sustainable Development Goals 12, 13 and 15 (United Nations, 2015a, p. 3) relating to sustainable production, climate action and life on land, respectively.

Agricultural waste contributes significantly to greenhouse gas (GHG) emissions if not adequately recycled and sustainably managed. A recurring agricultural waste is livestock waste that has consistently served as feedstock for biogas systems. The objective of this study was to assess the use of animal waste digestate to mitigate GHG emissions in agricultural fields. Wheat (Triticum spp. L.) was fertilized with different types of animal waste digestate (organic fertilizers) and synthetic nitrogen fertilizer (inorganic fertilizer). The 170 kg N/ha presented in digestates were split fertilized at an application rate of 90 and 80 kg N/ha. Emissions of GHGs (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) were monitored directly by a static chamber system. The soil and environmental variables were measured to determine their influence on GHG emissions. Emission peaks in N2O and CO2 after the first application of fertilizers with the emissions flattening out over the cultivating season while CH4 emission was negligible with no apparent patterns observed. Results showed individual and cumulative emissions of CO2, CH4 and N2O from the digestates were relatively low and digestate fertilization could be an efficient method for reducing GHGs from agricultural sources in temperate climate conditions.

Recent calls advocate that a huge reduction in the consumption of animal products (including dairy) is essential to mitigate climate change and stabilise global warming below the 1.5 and 2°C targets. The Paris Agreement states that to stabilise temperatures we must reach a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases (GHG) in the second half of this century. Consequently, many countries have adopted overall GHG reduction targets (e.g. EU, at least 40% by 2030 compared to 1990). However, using conventional metric-equivalent emissions (CO2-e GWP100) as the basis to account for emissions does not result in capturing the effect on atmospheric warming of changing emission rates from short-lived GHG (e.g. methane: CH4), which are the main source of GHG emissions by small ruminants. This shortcoming could be solved by using warming-equivalent emissions (CO2-we, GWP*), which can accurately link annual GHG emission rates to its warming effect in the atmosphere. In our study, using this GWP* methodology and different modelling approaches, we first examined the historical (1990–2018) contribution of European dairy small ruminant systems to additional atmosphere warming levels and then studied different emission target scenarios for 2100. These scenarios allow us to envision the necessary reduction of GHG emissions from Europe's dairy small ruminants to achieve a stable impact on global temperatures, i.e. to be climatically neutral. Our analysis showed that, using this type of approach, the whole European sheep and goat dairy sector seems not to have contributed to additional warming in the period 1990–2018. Considering each subsector separately, increases in dairy goat production has led to some level of additional warming into the atmosphere, but these have been compensated by larger emission reductions in the dairy sheep sector. The estimations of warming for future scenarios suggest that to achieve climate neutrality, understood as not adding additional warming to the atmosphere, modest GHG reductions of sheep and goat GHG would be required (e.g. via feed additives). This reduction would be even lower if potential soil organic carbon (SOC) from associated pastures is considered.

Methane (CH4) consumption in agricultural soil is imperative for the mitigation of climate change. However, the effect of tillage and cropping systems on CH4 consumption is less studied. Experiments were carried out in Madhya Pradesh, India with soybean-wheat (SW), maize-wheat (MW) and maize-gram (MG) cropping systems under conventional tillage (CT) and no-tillage (NT). Soybean/maize was cultivated during the kharif season (July–October) and wheat/chickpea in the rabi season (October–March) for 9 years consecutively. Soil samples were collected during vegetative growth stages of soybean and maize from different cropping systems. Methane consumption, the abundance of methanotrophs as particulate methane monooxygenase (pmoA) gene copies, soil and crop parameters were estimated. Methane consumption rate was higher in NT and upper soil layer (0–5 cm) than CT and 5–15 cm depth. Methane consumption rate k ranged from 0.35 to 0.56 μg CH4 consumed/g soil/d in the order of MW>SW>MG in 0–5 cm. The abundance of pmoA gene copies ranged from 43 × 104/g soil to 13 × 104/g soil and was highest in MW-NT and lowest in MG-CT. Available nitrogen, phosphorus and potassium were higher in 0–5 cm than in 5–15 cm depth. Soil and plant parameters and abundance of pmoA genes correlated significantly and positively with CH4 consumption rate. No-tillage stimulated CH4 consumption compared to CT irrespective of cropping system and CH4 consumption potential was highest in MW and lowest in MG. However, the magnitude of the positive effect of NT towards CH4 consumption was higher in SW and MG than MW.

Meat and milk from ruminants provide an important source of protein and other nutrients for human consumption. Although ruminants have a unique advantage of being able to consume forages and graze lands not suitable for arable cropping, 2% to 12% of the gross energy consumed is converted to enteric CH4 during ruminal digestion, which contributes approximately 6% of global anthropogenic greenhouse gas emissions. Thus, ruminant producers need to find cost-effective ways to reduce emissions while meeting consumer demand for food. This paper provides a critical review of the substantial amount of ruminant CH4-related research published in past decades, highlighting hydrogen flow in the rumen, the microbiome associated with methanogenesis, current and future prospects for CH4 mitigation and insights into future challenges for science, governments, farmers and associated industries. Methane emission intensity, measured as emissions per unit of meat and milk, has continuously declined over the past decades due to improvements in production efficiency and animal performance, and this trend is expected to continue. However, continued decline in emission intensity will likely be insufficient to offset the rising emissions from increasing demand for animal protein. Thus, decreases in both emission intensity (g CH4/animal product) and absolute emissions (g CH4/day) are needed if the ruminant industries continue to grow. Providing producers with cost-effective options for decreasing CH4 emissions is therefore imperative, yet few cost-effective approaches are currently available. Future abatement may be achieved through animal genetics, vaccine development, early life programming, diet formulation, use of alternative hydrogen sinks, chemical inhibitors and fermentation modifiers. Individually, these strategies are expected to have moderate effects (<20% decrease), with the exception of the experimental inhibitor 3-nitrooxypropanol for which decreases in CH4 have consistently been greater (20% to 40% decrease). Therefore, it will be necessary to combine strategies to attain the sizable reduction in CH4 needed, but further research is required to determine whether combining anti-methanogenic strategies will have consistent additive effects. It is also not clear whether a decrease in CH4 production leads to consistent improved animal performance, information that will be necessary for adoption by producers. Major constraints for decreasing global enteric CH4 emissions from ruminants are continued expansion of the industry, the cost of mitigation, the difficulty of applying mitigation strategies to grazing ruminants, the inconsistent effects on animal performance and the paucity of information on animal health, reproduction, product quality, cost-benefit, safety and consumer acceptance.