Nitrogen (N) limits primary productivity in much of the world. Since the 1940s, synthetic fertilizers produced via the conversion of unreactive atmospheric dinitrogen (N2) into reactive N have supported agricultural production but also perturbed natural nutrient cycles. In this Review, we compile estimates of global N cycling since 1955 and explore changes in the global N balance. Since the 1960s, the annual amount of reactive N entering the biosphere increased fivefold. Meanwhile, N emissions from the biosphere to the atmosphere increased just 12% between the oldest and latest estimates, indicating terrestrial N accumulation on the order of ~50 Tg N yr−1 between 1959 and 2025. The increased N availability due to these inputs has polluted soils, waters and air, negatively affecting ecosystems and economies. Quantifying N pools and fluxes across the atmospheric, terrestrial and aquatic reservoirs is critical to monitor and mitigate this imbalance in the N cycle. Reducing fertilizer demand and use through dietary changes, technological advances to enhance fertilizer efficiencies, and improvements to waste management and nutrient recycling could support a net flux of 51 Tg N yr−1 to the atmosphere, which could help address the existing imbalance in the global N cycle. Synthetic fertilizer use has perturbed the global nitrogen cycle by increasing reactive nitrogen inputs to terrestrial systems. This Review synthesizes estimates of global nitrogen pools and fluxes since 1955, assessing flux imbalances and identifying research and policy priorities to rebalance the global nitrogen cycle.
Biochar applications can help mitigate climate change, improve soil health and support a circular economy. Reducing production costs and safety risks, maximizing design and co-benefits, and scaling up to the carbon markets are key priorities in realizing this potential.
Fishing has long been a concern to ocean ecosystems, but it can also impact the carbon cycle by disturbing the biological carbon pump (BCP). This Comment discusses whether a ‘BCP fisheries code of practice’ could and should be developed to incentivize natural resource management mechanisms that protect the BCP.
Although sea ice covers only ~9% of the world’s oceans, its presence and absence greatly alter the energetic balance of Earth’s climate. Owing to geographic differences, Arctic and Antarctic sea ice have different dominant properties and processes, which in turn produce different responses to natural climate variability and anthropogenic climate change. This Review surveys the changes in sea-ice properties and processes of the Arctic and Antarctic environments. The Arctic melt season has lengthened by ~7.4 days per decade during 1979–2024, alongside decreases in winter sea-ice thickness (1.6 m mean total over 1980–2023), summer surface albedo (0.03 per decade over 1979–2020) and spring snow depth (2.5 cm per decade over 1954–2024). Changes in the Antarctic are smaller than those in the Arctic owing to contrasting regional and temporal trends. From a dynamic perspective, sea-ice motion in both hemispheres has increased, by 0.63 cm s–1 per decade in the Arctic (1978–2024) and 0.69 cm s–1 per decade in the Antarctic (1982–2024), whereas trends in polynya occurrence differ by region. This Review highlights major knowledge gaps and provides recommendations for joint model-observation efforts to improve understanding of sea ice and its role in Earth’s climate system. Sea ice modulates the energy exchange between the atmosphere and ocean through complex, time-varying processes. This Review describes changes in Arctic and Antarctic sea-ice properties and processes, discusses the future sea-ice environment and provides recommendations to improve understanding of sea ice and its role in Earth’s changing climate.
Suspended particulate matter (SPM) — composed of interacting minerals and organic matter — influences the transport and fate of carbon, nutrients and contaminants in all natural aquatic environments. In this Review, we synthesize physical, sedimentological and biogeochemical evidence to explore how and why SPM concentration, composition and size vary along the land–ocean continuum. Despite the large variability in SPM characteristics, its concentration is robustly correlated with its composition, size, density and settling velocity. In general, organic matter content and floc size increase with decreasing SPM concentration. In addition, flocs are small and consist mostly of minerals in turbidity maximum zones, with particle size and organic matter content increasing as waters become clearer. SPM concentrations also influence carbon partitioning, with the ratio of particulate to dissolved organic carbon increasing with SPM concentration. Therefore, SPM concentrations can reflect a combination of physical and biogeochemical processes and ecosystem properties. Climate change and human activities, such as dam construction and land use change, are perturbing SPM dynamics, with implications for wetland stability, contaminant mobility and carbon export and sequestration. Future research should prioritize in situ and remote sensing observations to constrain anthropogenic perturbations of SPM dynamics in natural systems and improve understanding of the implications for sediment accretion or erosion, pollutant mobility and the carbon cycle. Suspended particulate matter (SPM) influences the transport and fate of carbon and environmental contaminants in natural aquatic systems. This Review explores SPM dynamics along the land–ocean continuum and discusses how human activities and climate change might affect its role in the carbon cycle and sediment transport.
As the largest available freshwater resource, groundwater provides water for drinking and agricultural irrigation to billions of people worldwide. Subsurface environments are estimated to host over 30% of all microorganisms on Earth, with microbial communities having important roles in various groundwater processes. Discoveries of diverse and novel lineages of archaea, bacteria, microeukaryotes and viruses in groundwater have highlighted the key contributions of groundwater microbiomes to elemental cycling, contaminant degradation, pathogenicity and antimicrobial resistance. In this Review, we summarize the diversity and composition of prokaryotic, microeukaryotic and viral communities in groundwater, and describe the complex interactions between these different microbial groups. Groundwater microbiomes exhibit distinct biogeographic patterns, with key differences and similarities across groundwater types and other habitats. The community assembly of microorganisms across different groundwater environments is driven primarily by stochastic processes, whereas deterministic processes caused by environmental stress further modulate community structure and function. With regard to their function, groundwater microbiomes have crucial roles in shaping ecosystem functioning, including biogeochemical cycling, water quality and One Health. Finally, we highlight several future prospects for research to harness microbiomes as eco-sustainable solutions for groundwater restoration and protection in a changing world. Groundwater hosts a vast array of microbiomes that are essential to global water quality and ecosystem function. This Review discusses the diversity, biogeography and community assembly of the groundwater microbiome, and explores its role in biogeochemical cycling and sustainable groundwater management.
Plastic agricultural films (PAFs) are widely used to enhance crop productivity, with global use projected to reach 9–14 million tonnes (Mt) per year by 2030. However, their use has led to contamination of soils with microplastics (MPs), nanoplastics and associated chemical additives. In this Review, we synthesize evidence on the global use of PAFs, their environmental fate and strategies to enhance their sustainable application. PAFs deliver substantial agronomic benefits, enhancing crop yields by 7–48% and soil water retention by 9–25%. However, films fragment and degrade under physical erosion, elevated ultraviolet radiation, temperature, humidity, and microbial and faunal activity. As a result, PAF use generates 3–5 Mt yr−1 of largely unmanaged waste, contributing to widespread plastic pollution in agricultural soils. For example, MP concentrations can reach ~13,000 items per kilogram, with PAFs accounting for 10–30%. Conventional polyethylene films degrade slowly and primarily undergo physical fragmentation, whereas biodegradable films fragment more rapidly, with cases of ~30% converted to MPs within 2 years. However, complete mineralization remains limited even for biodegradable materials. Additives in PAFs, including poorly characterized non-intentionally added substances, further increase environmental and toxicological risks, and their release varies substantially with environmental conditions and film type. MPs and additives affect soil health, crop yields and nutrient cycles. Mitigation strategies include substitution with safer additives, developing biodegradable waste-derived bio-based polymers, and conventional film recycling. Future work should improve field monitoring, develop a global database of PAF use and composition, and implement policy innovations to support sustainable PAF systems. Plastic agricultural films enhance crop productivity and support food security, but their use also contaminates soils with plastics and chemical additives. This Review examines the global production and use of agricultural films, their environmental impacts, and strategies to support their sustainable production and use.
Wei Chen explains how differential pulse voltammetry is used to resolve the electron transfer processes underlying microbe–mineral element cycles in soils, sediments and aquifers.
Imaging spectroscopy technology is transforming the way Earth is viewed from space, with applications across diverse science communities. A global imaging spectrometer mission with Landsat-like spatial and temporal coverage could fully realize this potential.
Increasing contamination of rice paddies by toxic metal(loid)s from anthropogenic sources threatens food security and public health. In this Perspective, we outline the problem of metal(loid) contamination in paddy soils and propose an activity-centric framework for safeguarding rice production. Approximately 14–17% of croplands exceed safe thresholds for at least one toxic metal(loid), exposing 0.9–1.4 billion people to elevated ecological and health risks. Management strategies that reduce the total mass of toxic metal(loid)s in soils are useful for restoring sites with high metal(loid) concentrations. However, these approaches are expensive and interrupt crop production, making them poorly suited to most in-production rice paddies with low-to-moderate contamination. Activity-centric strategies aim to reduce metal(loid) bioavailability and plant uptake at the soil–water–root–grain continuum, offering a production-compatible alternative. An integrated risk management framework that bridges risk-informed implementation of technologies with localized policy governance to guide regional-scale metal(loid) management is proposed. Further research is needed to develop soil amendment materials and functional synthetic microbial communities that synergistically address metal(loid) contamination and actively contribute to overall soil health and resilience. Toxic metal(loid)s in paddy soils accumulate in rice grains, leading to human health risks from dietary metal exposure. This Perspective describes metal(loid) sources and biogeochemical strategies to reduce metal(loid) bioavailability and uptake, and it proposes a framework for coordinating science, policy and practice in contaminated paddy fields.
Nature Reviews Earth & Environment interviewed Junjie Wu about her project investigating Arctic subglacial carbon reactivity.
The Greenland Ice Sheet is a major contributor to global sea-level rise, having lost ~4,900 Gt of ice since 1992 and already added ~13 mm to global mean sea-level. Even without further warming, it is committed to at least ~274 mm of additional sea-level rise, and complete melting would ultimately raise sea level by ~7 m. In this Review, we synthesise changes in Greenland Ice Sheet surface melt from 1500 to 2200 CE. Surface melt has increased rapidly by ~1% per year since the 1990s, driven by regional warming and changes in atmospheric circulation, particularly enhanced blocking. Several unprecedented extreme melt events lasting several days have occurred since 2007, with record cases such as in July 2012 affecting nearly the entire ice sheet surface. Absorbed shortwave radiation is the dominant driver of seasonal melt, but turbulent heat fluxes, cloud processes and albedo feedbacks strongly modulate melt variability across space and time. Climate models diverge in their representation of these processes, with projected melt and surface mass loss differing by up to a factor of two between three different state-of-the-art regional climate models even under identical forcing. Despite advances in regional climate and Greenland melt modelling, key uncertainties remain in quantifying extreme melt events and their drivers, meltwater retention, firn processes and the coupling between atmospheric forcing and surface energy balance, limiting confidence in projections. Addressing these gaps requires expanded observations, improved process representation in models and integrated use of emerging data-driven approaches to better constrain future melt and its contribution to sea-level rise. Greenland Ice Sheet melt has intensified since the 1990s with implications for sea-level rise. This Review synthesises paleoclimate records, observations and regional climate melt model simulations to explore the patterns and drivers of melt variability and extremes, and assess uncertainties in future projections.
The redox state of the atmosphere and hydrosphere was essential to the origin of life on Earth and its long-term habitability. In this Review, we explore the formation and redox evolution of the Earth’s early atmosphere and hydrosphere, combining evidence from meteorites, the ancient rock record and numerical models. The initial atmosphere was formed by primordial volatile accretion, primary magma-ocean outgassing and secondary volatile outgassing after magma-ocean crystallization during the Hadean aeon (4.567–4.0 Ga). An initial hydrosphere could have developed as early as 4.4 Ga, but probably underwent episodic vaporization during late accretion. The earliest robust evidence of subaqueous environments is dated at about 3.7 Ga. The mantle reached its modern-day redox state between 4.4 Ga and 2.7 Ga. Free O2 in the hydrosphere appears at 3.0 Ga, whereas the initial rise of atmospheric O2 (the ‘Great Oxidation Event’) occurred later, at 2.5–2.3 Ga. This delay in the surface oxidation was probably caused by a synergy of geodynamic, magmatic and (bio)geochemical mechanisms modulating oxygen sources and sinks. These processes in turn shifted the dynamics of other volatile element cycles important to the evolution of life, such as nitrogen, carbon and hydrogen. Future work should prioritize determining further quantitative constraints on Earth’s oxygen sources and sinks through time to understand the habitability of early Earth. Understanding how Earth’s atmosphere and hydrosphere formed and evolved could help to explain how Earth became, and remains, habitable. This Review discusses the initial formation and redox evolution of Earth’s surface environments, with implications for other planetary bodies.
Intensive reliance on conventional synthetic agrochemicals has been linked to environmental degradation and human health risks. Integrating nano-agrochemicals into agricultural practices could boost yields and reduce environmental footprints. In this Review, we evaluate the functions, market penetration, and benefits and risks of nano-agrochemicals in terms of crop productivity, environmental outcomes and human health. Nano-agrochemical formulations, primarily nanofertilizers and nanopesticides, are designed for targeted delivery and enhanced efficacy. Despite their promise, nano-agrochemicals currently represent <1% share of the global agrochemical market. Nanoformulations can boost crop yields by approximately 20%, largely through increased nutrient-use efficiency. However, their performance depends on environmental factors, such as soil texture, pH and ionic strength, which govern nanoparticle stability. Application methods (foliar versus soil) further interact with biological factors, including the above-ground and below-ground microbiotas, leaf and root exudates, and soil fauna, to influence nano-agrochemical bioavailability and uptake by plants. Nanofertilizers reduce nutrient leaching and nanopesticides minimize non-target toxicity, collectively reducing environmental and human health risks. Monitoring and regulatory frameworks remain highly heterogeneous across regions, with contrasting approaches in major agricultural producers, including the European Union, USA, China, Brazil and India. Future work should prioritize a universal ‘One Health’ assessment framework coupled with comprehensive life-cycle analyses to harmonize risk evaluation and guide the responsible global deployment of nano-agrochemicals. Improving agrochemical efficacy is important for safely meeting increasing food demand and responding to environmental change. This Review examines how nano-agrochemicals could boost food production sustainably, discusses their risks and benefits, and outlines approaches to facilitate their safe deployment.
Addressing climate change requires knowledge of its impacts on both nature and people. This Review depicts current approaches to the attribution of climate change impacts and potential uses for this information. The discussion covers how impact attribution identifies the drivers of observed changes and events that form links in the causal chain from anthropogenic greenhouse gas emissions and other human-induced climate forcing factors to effects on natural and human systems mediated by changes in climate and weather. Various approaches are presented that use observations and/or model simulations to estimate how a world without climate change could have evolved. In addition, different societal uses of impact attribution results are discussed and how different study designs might support them. This Review also identifies persistent knowledge gaps that call for input from policy experts globally. For example, future tailored designs might enable the attribution of additional impacts and improve quantification of the role of climate change against other drivers, whereas increased transdisciplinary collaboration and organization might provide standardization that benefits data comparability and synthesis. Addressing the remaining challenges is expected to help the impact attribution community to produce targeted answers for well-framed questions that inform development, implementation and operationalization of climate policies. Climate change impact attribution quantifies the observed consequences of climate change through combining climate attribution aspects with impact modelling. Undorf et al. discuss the key steps and methodological choices required, possible societal uses of impact attribution results and ongoing challenges.
Dissolved oxygen (DO) supports aerobic respiration of aquatic organisms and biogeochemical cycles involved in nutrient cycling and organic matter decomposition. Widespread freshwater deoxygenation is threatening the health and function of aquatic systems. In this Review, we outline global trends, drivers, impacts and potential mitigation measures of deoxygenation in inland freshwater systems. Surface water DO concentrations have declined rapidly in lakes (–0.034 mg l–1 decade–1 in summer throughout 2003–2023) and rivers (–0.043 mg l–1 decade–1 year-round throughout 1980–2023). The highest rate of DO decline is in Asian lakes (–0.043 mg l–1 decade–1) and the Amazon River Basin (–0.2 mg l–1 decade–1); conversely, DO levels have increased in 25.4% of rivers, particularly in Western Africa and Southeast Asia. Climate warming amplifies deoxygenation through prolonged stratification, reduced DO solubility and increased microbial respiration. Human activities also contribute to deoxygenation; for example, agricultural runoff drives eutrophication and DO loss; this effect is exacerbated by extreme rainfall events. Deoxygenation creates positive biogeochemical feedbacks that accelerate ecosystem degradation and restructure biological communities. Additionally, deoxygenation has negative socioeconomic impacts, reducing fishing yields, demand for freshwater-based recreational activities and drinking water quality and availability. Improved management and mitigation of deoxygenation will require DO monitoring networks, nutrient management, ecological restoration, integrated DO predictive models and adaptive governance with stakeholder engagement. Widespread declines in dissolved oxygen concentrations in lakes and rivers have ecological and socioeconomic consequences. This Review highlights spatial and temporal trends, climate and anthropogenic drivers, impacts and strategies for the management and mitigation of inland freshwater deoxygenation.
Hydrogen has gained attention as a key component of future low-carbon energy and industrial systems, with demand projected to increase from 100 Mt per year in 2024 to up to 1,370 Mt per year in 2050. However, there are concerns about the climate impact of the associated increase in hydrogen emissions. In this Review, we discuss the sources and sinks of atmospheric hydrogen and the resulting climate effects, including the use of metrics and implications for policy. Despite not being a direct greenhouse gas, hydrogen raises levels of methane, tropospheric ozone and stratospheric water vapour, which are potent greenhouse gases. Estimates of the 100-year global warming potential of hydrogen converge at 12 ± 6 (90% CI). Such metrics are sufficiently robust to inform policy and business decision-making and to be included in climate impact assessments to maximize the benefits of a future hydrogen economy. However, substantial uncertainties remain, particularly in quantifying various sources of atmospheric hydrogen from human and natural systems (estimates have a range of 55–141 Tg per year) and understanding soil uptake rates (32–90 Tg per year). Future research should focus on improved quantification of hydrogen emissions, especially across the hydrogen system value chain, better constraints on the soil sink and a more complete representation of hydrogen chemistry. Although hydrogen is not a direct greenhouse gas, its interactions with atmospheric chemistry lead to indirect climate impacts. This Review discusses sources and sinks of atmospheric hydrogen, including uncertainties and data gaps, and how the warming effect of hydrogen emissions can be estimated and accounted for in policies and standards.
Globally, fires in 2025 burned the second-lowest area on record since 2002 and emitted the third-lowest CO2 total. Yet, a third successive year of extreme wildfire emissions prevailed in Canada, and catastrophic fires in Los Angeles, South Korea and Europe killed over 90 people and forced over 300,000 evacuations.
