Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N(2) fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N(2)O, NO and bi-directional NH(3) exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.

We use a soil carbon (C) model (RothC), driven by a range of climate models for a range of climate scenarios to examine the impacts of future climate on global soil organic carbon (SOC) stocks. The results suggest an overall global increase in SOC stocks by 2100 under all scenarios, but with a different extent of increase among the climate model and emissions scenarios. The impacts of projected land use changes are also simulated, but have relatively minor impacts at the global scale. Whether soils gain or lose SOC depends upon the balance between C inputs and decomposition. Changes in net primary production (NPP) change C inputs to the soil, whilst decomposition usually increases under warmer temperatures, but can also be slowed by decreased soil moisture. Underlying the global trend of increasing SOC under future climate is a complex pattern of regional SOC change. SOC losses are projected to occur in northern latitudes where higher SOC decomposition rates due to higher temperatures are not balanced by increased NPP, whereas in tropical regions, NPP increases override losses due to higher SOC decomposition. The spatial heterogeneity in the response of SOC to changing climate shows how delicately balanced the competing gain and loss processes are, with subtle changes in temperature, moisture, soil type and land use, interacting to determine whether SOC increases or decreases in the future. Our results suggest that we should stop looking for a single answer regarding whether SOC stocks will increase or decrease under future climate, since there is no single answer. Instead, we should focus on improving our prediction of the factors that determine the size and direction of change, and the land management practices that can be implemented to protect and enhance SOC stocks.

Agriculture is the largest anthropogenic source of methane (CH ₄ ), emitting 145 Tg CH ₄ y ⁻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 CH ₄ from these sources, with bottom-up mitigation potentials of approximately 10.6, 10, 2 and 1 Tg CH ₄ y ⁻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 CH ₄ y ⁻¹ from reduced enteric fermentation, and 4–36 Tg CH ₄ y ⁻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 CH ₄ 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 CH ₄ y ⁻¹ . While there is a pressing need to reduce emissions of long-lived greenhouse gases (CO ₂ and N ₂ O) due to their persistence in the atmosphere, despite CH ₄ 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 CH ₄ . This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part1)'.

To predict the response of C-rich soils to external change, models are needed that accurately\ud reflect the conditions of these soils. Estimation of Carbon in Organic Soils—Sequestration and\ud Emissions (ECOSSE) is a model that allows simulations of soil C and N turnover in both mineral and\ud organic soils using only the limited meteorological, land-use and soil data that is available at the\ud national scale. Because it is able to function at field as well as national scales if appropriate input data\ud are used, field-scale evaluations can be used to determine uncertainty in national simulations. Here\ud we present an evaluation of the uncertainty expected in national-scale simulations of Scotland, using\ud data from the National Soil Inventory of Scotland. This data set provides measurements of C change\ud for the range of soils, climates and land-use types found across Scotland. The simulated values show\ud a high degree of association with the measurements in both total C and change in C content of the\ud soil. Over all sites where land-use change occurred, the average deviation between the simulated\ud and measured values of percentage change in soil C was less than the experimental error (11% simulation\ud error, 53% measurement error). This suggests that the uncertainty in the national-scale simulations\ud will be ~11%. Only a small bias in the simulations was observed compared to the measured\ud values, suggesting that a small underestimate of the change in soil C should be expected at the\ud national scale (–4%