Abstract. Due to ongoing climate change, methane (CH4) emissions from vegetated wetlands are projected to increase during the 21st century, challenging climate mitigation efforts aimed at limiting global warming. However, despite reports of rising emission trends, a comprehensive evaluation and attribution of recent changes is still lacking. Here we assessed global wetland CH4 emissions from 2000 to 2020 based on an ensemble of sixteen process-based wetland models. Our results estimated global average wetland CH4 emissions at 158±24 (mean ± 1σ) Tg CH4 yr-1 for the period 2010–2020, with an average decadal increase of 6–7 Tg CH4 yr-1 compared to the decade of 2000–2009. The increases in the four latitudinal bands of 90° S–30° S, 30° S–30° N, 30° N–60° N, and 60° N–90° N were 0.1–0.2 Tg CH4 yr-1, 3.6–3.7 Tg CH4 yr-1, 1.8–2.4 Tg CH4 yr-1, and 0.6–0.8 Tg CH4 yr-1, respectively, over the two decades. The modeled CH4 sensitivities to temperature show reasonable consistency with eddy covariance-based measurements from 34 sites. Rising temperature was the primary driver of the increase, while precipitation and rising atmospheric CO2 concentrations played secondary roles with high levels of uncertainty. These modeled results suggest climate change is driving increased wetland CH4 emissions and that direct and sustained measurements are needed to monitor developments.
Dynamics of global wetlands are closely linked to biodiversity conservation, hydrology, and greenhouse gas emissions. However, long-term time series of global wetland products are still lacking. Using a TOPMODEL-based diagnostic model, we produced an ensemble of 28 gridded maps of monthly global/regional wetland extent products at 0.25° × 0.25° spatial resolution based on four observation-based wetland products and seven reanalysis soil moisture datasets for the period 1980–2020. The parameters of the model are calibrated on grid-scale against four observation-based wetland products. Overall, our products can capture the spatial distributions, seasonal cycles, and interannual variabilities of observed wetland extent well, and also show a good agreement with satellite-based terrestrial water storage estimates. The resulting mean annual maximum global wetland area fluctuates within a range of 3.3–5.6 Mkm2. The long temporal coverage beyond the era of satellite datasets, the global coverage and the opportunity to provide real-time update from ongoing SM data make these products helpful for various applications such as analyzing the wetland-related methane emission.
Abstract. The surface energy budget plays a critical role in terrestrial hydrologic and biogeochemical cycles. Nevertheless, its highly spatial heterogeneity across different vegetation types is still missing in the land surface model, ORCHIDEE-MICT (ORganizing Carbon and Hydrology in Dynamic EcosystEms–aMeliorated Interactions between Carbon and Temperature). In this study, we describe the representation of a multi-tiling energy budget in ORCHIDEE-MICT, and assess its short and long-term impacts on energy, hydrology, and carbon processes. With the specific values of surface properties for each vegetation type, the new version presents warmer surface and soil temperatures, wetter soil moisture, and increased soil organic carbon storage across the Northern Hemisphere. Despite reproducing the absolute values and spatial gradients of surface and soil temperatures from satellite and in-situ observations, the considerable uncertainties in simulated soil organic carbon and hydrologic processes prevent an obvious improvement of temperature bias existing in the original ORCHIDEE-MICT. However, the separation of sub-grid energy budgets in the new version improves permafrost simulation greatly by accounting for the presence of discontinuous permafrost type, which will facilitate various permafrost-related studies in the future.
An underwater glider is a type of autonomous profiling instrument platform used for gathering data to explore the ocean. Having a neutrally buoyant glider hull is one way to improve the glider's endurance with a passive compensation for buoyancy change. This article applies the bi-directional evolutionary structural optimization (BESO) method to the optimization of an underwater glider hull, based on two materials. Firstly, the method for determining the glider's neutral buoyancy is carried out. Secondly, the optimization problem is defined and the optimization procedure is presented. In the BESO procedure, the original design area elements with low strain energy are iteratively switched from high-value materials to low-value materials until a prescribed fraction is reached. Finally, an optimal underwater glider design is generated and the result demonstrates a reasonable material distribution of the neutrally buoyant glider hull. A 26.4% buoyancy adjustment is achieved and the mass of the glider is decreased by 31%.
Record breaking atmospheric methane growth rates were observed in 2020 and 2021 (15.2±0.4 and 17.6±0.5ppb yr -1 ), reaching their highest level since the commencement of ground-based observations in the early 1980s.Here we use an ensemble of atmospheric inversions informed by surface or satellite methane concentration observations to infer emission changes during these two years relative to 2019.We found a global increases of methane emissions of 20.3±9.9Tg CH4 in 2020 and 24.8±3.1 Tg CH4 in 2021.The emission rise was dominated by tropical and boreal regions with inundated areas, as a result of elevated groundwater table.Strong, synchronous, and persistent emission increases occurred in regions such as the Niger River basin, the Congo basin, the Sudd swamp, the Ganges floodplains and Southeast Asian deltas and the Hudson Bay lowlands.These regions alone contributed about 70% and 60% of the net global increases in 2020 and 2021, respectively.Comparing our top-down estimates with simulation of wetland emissions by biogeochemical models, we find that the bottom-up models significantly underestimate the intra-and inter-annual variability of methane sources from tropical inundated areas.This discrepancy likely arises from the models' limitations in accurately representing the dynamics of tropical wetland extents and the response of methane emissions to environmental changes.Our findings demonstrate the critical role of tropical inundated areas in the recent surge of methane emissions and highlight the value of integrating multiple data streams and modeling tools to better constrain tropical wetland emissions. MainIn the years 2020 and 2021, the methane growth rate (MGR) in the atmosphere reached 15.2±0.4 and 17.6±0.5parts per billion per year (ppb yr -1 ) respectively, hitting record high since systematic measurements started in early 1980s by NOAA's Global Monitoring Laboratory (GML) (Lan et al., 2023; https://gml.noaa.gov/ccgg/trends_ch4/).The unprecedented methane growth during 2020 and 2021 coincided with the reduced human activities and pollutant emissions during COVID-19 lockdowns and the gradual recovery
Abstract. The surface energy budget plays a critical role in terrestrial hydrologic and biogeochemical cycles. Nevertheless, its highly spatial heterogeneity across different vegetation types is still missing in the land surface model, ORCHIDEE-MICT (ORganizing Carbon and Hydrology in Dynamic EcosystEms–aMeliorated Interactions between Carbon and Temperature). In this study, we describe the representation of a multi-tiling energy budget in ORCHIDEE-MICT, and assess its short and long-term impacts on energy, hydrology, and carbon processes. With the specific values of surface properties for each vegetation type, the new version presents warmer surface and soil temperatures, wetter soil moisture, and increased soil organic carbon storage across the Northern Hemisphere. Despite reproducing the absolute values and spatial gradients of surface and soil temperatures from satellite and in-situ observations, the considerable uncertainties in simulated soil organic carbon and hydrologic processes prevent an obvious improvement of temperature bias existing in the original ORCHIDEE-MICT. However, the separation of sub-grid energy budgets in the new version improves permafrost simulation greatly by accounting for the presence of discontinuous permafrost type, which will facilitate various permafrost-related studies in the future.
In 2023, the CO2 growth rate was 3.37 +/- 0.11 ppm at Mauna Loa, 86% above the previous year, and hitting a record high since observations began in 1958, while global fossil fuel CO2 emissions only increased by 0.6 +/- 0.5%. This implies an unprecedented weakening of land and ocean sinks, and raises the question of where and why this reduction happened. Here we show a global net land CO2 sink of 0.44 +/- 0.21 GtC yr-1, the weakest since 2003. We used dynamic global vegetation models, satellites fire emissions, an atmospheric inversion based on OCO-2 measurements, and emulators of ocean biogeochemical and data driven models to deliver a fast-track carbon budget in 2023. Those models ensured consistency with previous carbon budgets. Regional flux anomalies from 2015-2022 are consistent between top-down and bottom-up approaches, with the largest abnormal carbon loss in the Amazon during the drought in the second half of 2023 (0.31 +/- 0.19 GtC yr-1), extreme fire emissions of 0.58 +/- 0.10 GtC yr-1 in Canada and a loss in South-East Asia (0.13 +/- 0.12 GtC yr-1). Since 2015, land CO2 uptake north of 20 degree N declined by half to 1.13 +/- 0.24 GtC yr-1 in 2023. Meanwhile, the tropics recovered from the 2015-16 El Nino carbon loss, gained carbon during the La Nina years (2020-2023), then switched to a carbon loss during the 2023 El Nino (0.56 +/- 0.23 GtC yr-1). The ocean sink was stronger than normal in the equatorial eastern Pacific due to reduced upwelling from La Nina's retreat in early 2023 and the development of El Nino later. Land regions exposed to extreme heat in 2023 contributed a gross carbon loss of 1.73 GtC yr-1, indicating that record warming in 2023 had a strong negative impact on the capacity of terrestrial ecosystems to mitigate climate change.
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