The growth rate of the atmospheric abundance of methane (CH ₄ ) reached a record high of 15.4 ppb yr ⁻¹ between 2020 and 2022, but the mechanisms driving the accelerated CH ₄ growth have so far been unclear. In this work, we use measurements of the ¹³ C: ¹² C ratio of CH ₄ (expressed as δ ¹³ C _CH4 ) from NOAA’s Global Greenhouse Gas Reference Network and a box model to investigate potential drivers for the rapid CH ₄ growth. These measurements show that the record-high CH ₄ growth in 2020–2022 was accompanied by a sharp decline in δ ¹³ C _CH4 , indicating that the increase in CH ₄ abundance was mainly driven by increased emissions from microbial sources such as wetlands, waste, and agriculture. We use our box model to reject increasing fossil fuel emissions or decreasing hydroxyl radical sink as the dominant driver for increasing global methane abundance.

Nitrogen isotope fractionations between nitrogen oxides (NO and NO₂) play a significant role in determining the nitrogen isotopic compositions (δ¹⁵N) of atmospheric reactive nitrogen. Both the equilibrium isotopic exchange between NO and NO₂ molecules and the isotope effects occurring during the NO_x photochemical cycle are important, but both are not well constrained. The nighttime and daytime isotopic fractionations between NO and NO₂ in an atmospheric simulation chamber at atmospherically relevant NO_x levels were measured. Then, the impact of NO_x level and NO₂ photolysis rate on the combined isotopic fractionation (equilibrium isotopic exchange and photochemical cycle) between NO and NO₂ was calculated. It was found that the isotope effects occurring during the NO_x photochemical cycle can be described using a single fractionation factor, designated the Leighton cycle isotope effect (LCIE). The results showed that at room temperature, the fractionation factor of nitrogen isotopic exchange is 1.0289±0.0019, and the fractionation factor of LCIE (when O₃ solely controls the oxidation from NO to NO₂) is 0.990±0.005. The measured LCIE factor showed good agreement with previous field measurements, suggesting that it could be applied in an ambient environment, although future work is needed to assess the isotopic fractionation factors of $\mathrm{NO}+{\mathrm{RO}}_{\mathrm{2}}/{\mathrm{HO}}_{\mathrm{2}}\to {\mathrm{NO}}_{\mathrm{2}}$ . The results were used to model the NO–NO₂ isotopic fractionations under several NO_x conditions. The model suggested that isotopic exchange was the dominant factor when NO_x>20 nmol mol⁻¹, while LCIE was more important at low NO_x concentrations (<1 nmol mol⁻¹) and high rates of NO₂ photolysis. These findings provided a useful tool to quantify the isotopic fractionations between tropospheric NO and NO₂, which can be applied in future field observations and atmospheric chemistry models.

In the face of ongoing and projected climatic changes, precipitation manipulation experiments (PMEs) have produced a wealth of data about the effects of precipitation changes on soils. In response, researchers have undertaken a number of synthetic efforts. Several meta-analyses have been conducted, each revealing new aspects of soil responses to precipitation changes. Here, we conducted a comparative analysis of the findings of 16 meta-analyses focused on the effects of precipitation changes on 42 soil response variables, covering a wide range of soil processes. We examine responses of individual variables as well as more integrative responses of carbon and nitrogen cycles. We find strong agreement among meta-analyses that belowground carbon and nitrogen cycling accelerate under increased precipitation and slow under decreased precipitation, while bacterial and fungal communities are relatively resistant to decreased precipitation. Much attention has been paid to fluxes and pools in carbon, nitrogen, and phosphorus cycles, such as gas emissions, soil carbon, soil phosphorus, extractable nitrogen ions, and biomass. The rates of processes underlying these variables (e.g., mineralization, fixation, and (de)nitrification) are less frequently covered in meta-analytic studies, with the major exception of respiration rates. Shifting scientific attention to these less broadly evaluated processes would deepen the current understanding of the effects of precipitation changes on soil and provide new insights. By jointly evaluating meta-analyses focused on a wide range of variables, we provide here a holistic view of soil responses to changes in precipitation.