Warming can accelerate the decomposition of soil organic matter and stimulate the release of soil greenhouse gases (GHGs), but to what extent soil release of methane (CH4) and nitrous oxide (N2O) may contribute to soil C loss for driving climate change under warming remains unresolved. By synthesizing 1,845 measurements from 164 peer‐reviewed publications, we show that around 1.5°C (1.16–2.01°C) of experimental warming significantly stimulates soil respiration by 12.9%, N2O emissions by 35.2%, CH4 emissions by 23.4% from rice paddies, and by 37.5% from natural wetlands. Rising temperature increases CH4 uptake of upland soils by 13.8%. Warming‐enhanced emission of soil CH4 and N2O corresponds to an overall source strength of 1.19, 1.84, and 3.12 Pg CO2‐equivalent/year under 1°C, 1.5°C, and 2°C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO2/year in terms of contribution to climate change. The warming‐induced rise in soil CH4 and N2O emissions (1.84 Pg CO2‐equivalent/year) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO2/year) under warming. Soil respiration and CH4 release are intensified following the mean warming threshold of 1.5°C scenario, as compared to soil CH4 uptake and N2O release with a reduced and less positive response, respectively. Soil C loss increases to a larger extent under soil warming than under canopy air warming. Warming‐raised emission of soil GHG increases with the intensity of temperature rise but decreases with the extension of experimental duration. This synthesis takes the lead to quantify the ecosystem C and N cycling in response to warming and advances our capacity to predict terrestrial feedback to climate change under projected warming scenarios.

Inland waters (rivers, reservoirs, lakes, ponds, streams) and estuaries are significant emitters of methane (CH 4 ) and nitrous oxide (N 2 O) to the atmosphere, while global estimates of these emissions have been hampered due to the lack of a worldwide comprehensive data set of CH 4 and N 2 O flux components. Here, we synthesize 2997 in-situ flux or concentration measurements of CH 4 and N 2 O from 277 peer-reviewed publications to estimate global CH 4 and N 2 O emissions from inland waters and estuaries. Inland waters including rivers, reservoirs, lakes, and streams together release 95.18 Tg CH 4 year −1 (ebullition plus diffusion) and 1.48 Tg N 2 O year −1 (diffusion) to the atmosphere, yielding an overall CO 2 -equivalent emission total of 3.06 Pg CO 2 year −1 . The estimate of CH 4 and N 2 O emissions represents roughly 60% of CO 2 emissions (5.13 Pg CO 2 year −1 ) from these four inland aquatic systems, among which lakes act as the largest emitter for both CH 4 and N 2 O. Ebullition showed as a dominant flux component of CH 4 , contributing up to 62%-84% of total CH 4 fluxes across all inland waters. Chamber-derived CH 4 emission rates are significantly greater than those determined by diffusion model-based methods for commonly capturing of both diffusive and ebullitive fluxes. Water dissolved oxygen (DO) showed as a dominant factor among all variables to influence both CH 4 (diffusive and ebullitive) and N 2 O fluxes from inland waters. Our study reveals a major oversight in regional and global CH 4 budgets from inland waters, caused by neglecting the dominant role of ebullition pathways in those emissions. The estimated indirect N 2 O EF 5 values suggest that a downward refinement is required in current IPCC default EF 5 values for inland waters and estuaries. Our findings further indicate that a comprehensive understanding of the magnitude and patterns of CH 4 and N 2 O emissions from inland waters and estuaries is essential in defining the way of how these aquatic systems will shape our climate.

Gaseous reactive nitrogen (Nr) emissions from agricultural soils to the atmosphere constitute an integral part of global N cycle, directly or indirectly causing climate change impacts. The extensive use of N fertilizer in crop production will compromise our efforts to reduce agricultural Nr emissions in China. A national inventory of fertilizer N-induced gaseous Nr emissions from croplands in China remains to be developed to reveal its role in shaping climate change. Here we present a data-driven estimate of fertilizer N-induced soil Nr emissions based on regional and crop-specific emission factors (EFs) compiled from 379 manipulative studies. In China, agricultural soil Nr emissions from the use of synthetic N fertilizer and manure in 2018 are estimated to be 3.81 and 0.73 Tg N yr −1 , with a combined contribution of 23%, 20% and 15% to the global agricultural emission total of ammonia (NH 3 ), nitrous oxide (N 2 O) and nitric oxide (NO), respectively. Over the past three decades, NH 3 volatilization from croplands has experienced a shift from a rapid increase to a decline trend, whereas N 2 O and NO emissions always maintain a strong growth momentum due to a robust and continuous rise of EFs. Regionally, croplands in Central south (1.51 Tg N yr −1 ) and East (0.99 Tg N yr −1 ) of China exhibit as hotspots of soil Nr emissions. In terms of crop-specific emissions, rice, maize and vegetable show as three leading Nr emitters, together accounting for 61% of synthetic N fertilizer-induced Nr emissions from croplands. The global warming effect derived from cropland N 2 O emissions in China was found to dominate over the local cooling effects of NH 3 and NO emissions. Our established regional and crop-specific EFs for gaseous Nr forms provide a new benchmark for constraining the IPCC Tier 1 default EF values. The spatio-temporal insight into soil Nr emission data from N fertilizer application in our estimate is expected to advance our efforts towards more accurate global or regional cropland Nr emission inventories and effective mitigation strategies. K E Y W O R D S climate change, emission factor, fertilizer, nitrogen use efficiency, reactive nitrogen 1 | INTRODUC TI ON Reactive nitrogen (Nr) into and out of terrestrial ecosystems plays a critical role in global N cycle (Sutton et al., 2013). In general, gaseous Nr emissions have long-lived warming effects from the production of nitrous oxide (N 2 O) and tropospheric ozone (O 3 ), along with short-lived cooling effects by changing tropospheric aerosol, methane (CH 4 ) and O 3 (Galloway et al., 2008). Worldwide rapid growth | 1009 MA et Al.

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