Uncertainties around net‐zero climate targets have major impact on greenhouse gas emissions projections

Globally, more than 100 countries have adopted net-zero targets. Most studies agree on how this increases the chance of keeping end-of-century global warming below 2°C. However, they typically make assumptions about net-zero targets that do not capture uncertainties related to gas coverage, sector coverage, sinks, and removals. This study aims to analyze the impact of many uncertainty factors on the projected greenhouse gas (GHG) emissions by 2050 for major emitting countries following their net-zero pathways, and their aggregate impact on global GHG emissions. Global emission projections range from 23 to 40 gigatons of CO2 equivalent (GtCO2eq), with a median of 31 GtCO2eq. Our full range corresponds to about 40-75% of 2015 emission levels, which is much wider than the range of 30-45% reported by various integrated assessment models. The main factors contributing to this divergence are the uncertainty in the gas coverage of net-zero targets and uncertainty in the socioeconomic baseline. Countries with net-zero GHG targets by 2050 have a small range of 2050 emissions, while countries with net-zero targets beyond 2050 and unclear coverage, such as China, India, and Indonesia, have a large range of emissions by 2050

Current and future research in environmental sustainability: Synthesise of the role, responsibilities, and opportunities for the business sector

Environmental sustainability is a timely and important topic to investigate given the increasingly complex challenges requiring businesses to reevaluate their business models in relationships with the natural environment, including their roles and responsibilities, and how opportunities in addressing these challenges may be utilized. This special issue enhances contemporary and future research by soliciting a wide variety of themes from ten papers falling under the scope of an ecological and climate focus of environmental sustainability relevant to the roles, responsibilities, and opportunities for the business sector, while also considering the links between environmental and social aspects. The articles included in the special issue provide an overview of five topics. These are 1) sub-national greenhouse gas accounting approaches, 2) corporate governance, policies, and practices, 3) sustainable finance, 4) consumer viewpoints and expectations, and 5) bioeconomy. Moreover, the crosscutting themes discussed suggest an inter- and transdisciplinary nature of environmental sustainability. In this introductory article to the special issue, the ten articles bring forth national and institutional levels, the sub-national level, and the organizational level. To conclude, future research avenues are vast based on suggestions presented in the ten papers the special issue covers. However, this introductory article also brings up topics suggested in the initial call for papers but were not covered in the papers included in the special issue, thus still relevant for future studies

Warming Promotes Nitrogen and Carbon Cycles in Global Grassland

Grasslands, standing as one of Earth’s major ecosystems, offer numerous services vital to human well-being. The productivity of grasslands hinges on the availability of soil reactive nitrogen, which is highly sensitive to climatic variations. Using an extensive synthesis of 1242 experimental observations, reinforced by multiple models, we show that warming as a single driver of climate change intensifies nitrogen dynamics in grasslands. This could lead to increases in net primary productivity of 1% to 9% and escalate nitrogen leakage into the environment by 22% to 141%. Under the warming SSP2-4.5 scenario, we foresee an annual boost of 17 million tons per year (Tg yr–1) of nitrogen inputs, predominantly via biological nitrogen fixation, compared to the baseline scenario by 2050. Total nitrogen harvest is projected to climb by 12 Tg yr–1. However, the nitrogen surplus surge is expected to increase by 5 Tg yr–1, potentially intensifying nitrogen pollution. To counter this, adaptation measures must aim at curtailing reactive nitrogen losses while preserving increased nitrogen harvest. This could reduce nitrogen input and surplus by 10 and 20 Tg yr–1, respectively, while boosting nitrogen harvest by 10 Tg yr–1, potentially yielding economic gains of up to 121 billion USD by 2050. In shaping climate change adaptation policies, it is critical to balance the potential benefits and drawbacks of forging effective management approaches

A principle-based framework to determine countries’ fair warming contributions to the Paris Agreement

Equity is a cornerstone of global climate policy, yet differing perspectives mean that international agreement on how to allocate mitigation efforts remains elusive. A rich literature informs this question, but a gap remains in approaches that appropriately consider non-CO2 emissions and their warming contributions. In this study, we address this gap and define a global warming budget applicable to all anthropogenic greenhouse gases that is allocated to countries based on principles drawn from international treaties and environmental law. We find that by 2021 a range of 84 to 90 countries, including but not limited to all major developed countries, exhausted their budget share compatible with keeping warming to 1.5 °C (with 50% likelihood) under all allocation approaches considered in this study. A similar picture emerges for limiting warming to 2 °C (with 67% likelihood). A large group of countries will hence exceed their fair shares even if their pledges under the Paris Agreement represent their deepest possible emission reductions. Considerations of fairness should therefore start exploring aspects beyond domestic emissions reductions

Electricity- and hydrogen-driven energy system sector-coupling in net-zero CO2 emission pathways

Electricity- and hydrogen-based sector coupling contributes to realizing the transition towards greenhouse gas neutrality in the European energy system. Energy system and integrated assessment models show that, to follow pathways compatible with the European policy target of net-zero greenhouse gas emissions by 2050, large amounts of renewable electricity and H2 need to be generated, mostly by scaling-up wind and solar energy production capacity. With a set of such models, under jointly adopted deep decarbonisation scenario assumptions, we here show that the ensuing direct penetration of electricity and H2 in final energy consumption may rise to average shares of around 60% and 6%, respectively, by 2050. We demonstrate that electrification proves the most cost-efficient decarbonisation route in all economic sectors, while the direct use of H2 in final energy consumption provides a relatively small, though essential, contribution to deep decarbonisation. We conclude that the variance observed across results from different models reflects the uncertainties that abound in the shape of deep decarbonisation pathways, in particular with regard to the role of H2

The inoculation dilemma: Partial vs Full immunization during the early rollout in a pandemic

COVID-19 demonstrated the extent to which a pandemic can affect billions of lives worldwide. Vaccinations are an effective intervention that reduces the burden of the disease on the population. However, the low availability of vaccine doses coupled with an emerging infection wave calls for efficient dose allocation. We study the tradeoffs between prioritization of partial or full immunization while allocating limited doses with the help of an augmented SIR model. We define the term allocation ratio as the ratio of doses allocated for partial immunization as a proportion of the total available doses. Optimal control theory is used to derive the path traversed by the allocation ratio throughout the vaccine administration program. Numerical insights are obtained by introducing the case study of the Indian state of Tamil Nadu. Results indicate a preference towards full immunization when the active infections are low, while a switch to exclusive partial immunization is observed as the infection wave grows. Sensitivity analysis shows that factors like reduced vaccine availability, higher transmission rate, and high first-dose efficacy promote a quicker switch. The results also indicate significant potential savings of around ₹710 billion (∼ $8.46 billion) in mortality losses compared to the more widely followed pro-rata allocation policies. Hence, our study contributes to the growing discussion around the optimal strategy for vaccine administration with a focus on dose prioritization. The results of our research can help policymakers determine the allocation of limited available doses when faced with rising infection numbers during future pandemics

Statistical Distribution of Urban Area Reveals a Converging Trend of Global Urban Land Expansion

Urban land expansion is a major driver of many environmental and societal changes that challenge human well-being and sustainable development, but its evolutionary process and dynamics are neither clear nor well-integrated into urban science quantitatively. We analyzed the global urban extent data based on nighttime lights to examine the statistical distribution of urban land area at the global scale, and in 13 regions and countries over 29 years. The results reveal a converging temporal trend in urban land expansion from subnational to global scales, characterized by a coherent shift of urban area distribution from an initial power law toward an exponential distribution. This trend is well captured by a unified mathematical model based on the shifted power law distribution function and is reflected in the gradual predominance of medium-size cities over small-size cities in the configuration of urban systems across the world. The shift of urban area distributions bears the consequence of reduced urban system stability and resilience, and can be linked to increasing exposure of urban populations to extreme heat events and air pollution. These changes are likely to be driven by the increasing influence of external economies of scale associated with globalization. The findings challenge the status quo of land urbanization practices and emphasize the importance of medium-size cities in urban planning

Inequities blocking the path to circular economies: A bio-inspired network-based approach for assessing the sustainability of the global trade of waste metals

Considering the importance of waste metals for the transition to circular economies, this study follows a bioinspired approach to evaluate their material and monetary global trade patterns for sustainability and equity. Between 2000 and 2022, the global trade grew by 5 % in trading countries, by 37 % in trade links, by 71 % in material flows, and by 569 % in economic flows. Driven by indirect effects, the average circulation of material and monetary flows ranged between 21.8-34.9 - 34.9 % depending on the demand or supply perspective but showed a declining trend. Due to homogenization, high network redundancy, and low network efficiency the trade remained robust yet outside the "window of vitality" characterizing natural ecosystems. A few, mostly high-income countries dominated the market, consolidating imports of high-value metal waste mostly from low- and middle- income exporters. Policies should address circularity and trade inequities, accounting for environmental and social ramifications throughout the lifecycle of products and materials

A dataset of structural breaks in greenhouse gas emissions for climate policy evaluation

The quantitative assessment of policies aimed at climate change mitigation requires rigorously identifying abnormal changes in greenhouse gas emissions. We present a new dataset of robust level changes in greenhouse gas emissions that cannot be explained by aggregate socioeconomic fluctuations. Modern methods of structural break identification based on two-way fixed effects models are employed to estimate the size of significant level changes in emissions. The resulting dataset spans information for all major greenhouse gases in OECD countries across 37 IPCC sectors, from 1995 to 2022. The data unveils large differences in abnormal changes in emissions across gases, countries and sectors, as well as over time. Our resulting data can be applied to a broad range of research questions, including the analysis of the comparative efficacy of policy instruments to mitigate climate change

Place attachment, activation of personal norms, and the role of emotions to save water in scarcity

Water bodies across (semi)arid regions are being pressured by climate change and agriculture. Aptly, in Iran, Urmia Lake's fate is in contestation of these two stressors. Whereas climate change mitigation mandates a huge far-lasting global endeavor, some regional adaptations may support the lake to survive ecologically. This needs accountable actions by both institutions and individuals, contributing to the agricultural dynamism. To ensure the effectiveness of institutional lake restoration plans, the consent, cooperation, and active participation of farmers are essential. The critical issue is to know how to persuade farmers and foster prudent water consumption as the prime strategy. This requires understanding farmers intention and behavior in relation to water conservation. To explore this in the region, a specific sociopsychological model was developed. Utilizing the Norm Activation Model enriched by the constructs of Place Attachment and Expression of Emotion, farmers' moral water conservation behavior in the Urmia Lake Basin was investigated. The results of structural equation modeling revealed that all factors of the model influence the water conservation intention and behavior. While awareness of consequences strongly affects personal norms and appraisal of responsibility, place attachment and appraisal of responsibility positively impact emotions and correspondingly emotions and place attachment affect intention significantly. Whereas personal norms were influenced by awareness of consequences and appraisal of responsibility, they impact behavior and intention significantly and eventually intention makes the strongest relationship with behavior. Uncovering this, the study aims to expose further pragmatic insights for credible and sustainable environmental management policies