Methane

Methane emissions are responsible for approximately $0.5$$°\mathrm{C}$, or about 30%, of total greenhouse-gas-induced warming. For many countries, methane represents an even larger share of their overall warming footprint. Assessing the warming contributions of individual methane-emitting countries to global warming is not straightforward due to methane’s short atmospheric lifetime and the non-linear (convex) relationship between radiative forcing and the atmospheric concentration of this gas. This study addresses this challenge using a simple climate model in combination with a warming allocation approach derived from cooperative game theory. Applying this method, the warming contributions of several high-methane-emitting countries and regional groupings are quantified relative to the early industrial period. The analysis reveals that the commonly used marginal attribution method underestimates methane-induced warming by approximately 20%. This discrepancy is due to the substantial rise in the atmospheric concentration of methane since early industrial times.

This study assessed the effects of NiFe-based metal catalysts on CO₂ conversion to methane (CH₄) and carboxylic acids in microbial electrosynthesis (MES) cells. A NiFeBi alloy, when electrodeposited on a conductive bioring cathode, significantly decreased CH₄ production from 0.55 to 0.12 L (Lc d)⁻¹ while enhancing acetate production to 1.0 g (Lc d)⁻¹, indicating suppressed methanogenic activity and improved acetogenic activity. On the other hand, NiFeMn and NiFeSn catalysts showed varied effects, with NiFeSn increasing both CH₄ and acetate production and suggesting potential in promoting both chain elongation and CO₂ uptake. When these alloys were electrodeposited on a 3D-printed conductive polylactide (cPLA) lattice, the production of longer-chain carboxylic acids like butyrate and caproate increased significantly, indicating enhanced biocompatibility and nutrient delivery. The NiFeSn-coated cPLA lattice increased caproate production, which was further enhanced using an acetogenic enrichment. However, the overall throughput remained low at 0.1 g (Lc d)⁻¹. Cyclic voltammetric analysis demonstrated improved electrochemical responses with catalyst coatings, indicating better electron transfer. These findings underscore the importance of catalyst selection and cathode design in optimizing MES systems for efficient CO₂ conversion to value-added products, contributing to environmental sustainability and industrial applications.

Accurate methane emission estimates are essential for climate policy, yet current field methods often struggle with spatial constraints and source complexity. Ground-based mobile approaches frequently miss key plume features, introducing bias and uncertainty in emission rate estimates. This study addresses these limitations by using small unmanned aerial systems equipped with precision gas sensors to measure methane alongside co-released tracers. We tested whether arc-shaped flight paths and alternative ratio estimation methods could improve the accuracy of tracer-based emission quantification under real-world constraints. Controlled releases using ethane and nitrous oxide tracers showed that (1) arc flights provided stronger plume capture and higher correlation between methane and tracer concentrations than traditional flight paths; (2) the cumulative sum method yielded the lowest relative error (as low as 3.3%) under ideal mixing conditions; and (3) the arc flight pattern yielded the lowest relative error and uncertainty across all experimental configurations, demonstrating its robustness for quantifying methane emissions from downwind plume measurements. These findings demonstrate a practical and scalable approach to reducing uncertainty in methane quantification. The method is well-suited for challenging environments and lays the groundwork for future applications at the facility scale.