Siderite has a debated formation route — abiotic or microbially mediated — with implications for both the early Earth and Mars, as Neha Mehta explains.
Satellites are revolutionizing our ability to observe forest ecosystems from space, especially when integrated with field observations, experiments and models. The greatest challenge is no longer a lack of observations, but rather the integration of information and knowledge across scales to better understand resilience, guide recovery and inform action on the coupled crises of biodiversity and climate.
Biocrusts can substantially enhance snow retention, sustaining soil biogeochemistry, microbial activity and soil ecosystem functions in cold deserts, according to a long-term field study of how moss-dominated biocrust cover influences snow cover duration and depth.
The build-up of soil organic carbon depends less on the amount of substrate carbon available but more on the energy soil microbes can use to grow and leave behind residues, according to a global analysis of microbial energy demand and the energy contained in substrate carbon.
Nature Geoscience spoke with Ana Bastos (Leipzig University, Germany) and Sonia I. Seneviratne (ETH Zürich, Switzerland) about how climate change is reshaping forest ecosystems, how forests and land-use change feedback on the climate system, and what this means for land-based climate mitigation strategies.
Nature-based solutions in savannas and grasslands that seek to maximize tree cover and carbon uptake can erode biodiversity, create fragile carbon stocks and disrupt the livelihoods of people who depend on these landscapes, all for uncertain climate benefits.
Tropical forests are increasingly affected by drought, yet the factors that control post-drought ecosystem resilience—the capacity to withstand disturbances—are not fully understood. Here we use temporal autocorrelation of satellite-derived vegetation greenness to quantify ecosystem resilience following 142,444 severe drought events across tropical forests from 2003 to 2022. We show that resilience declined in 68.8% of areas after droughts, particularly in dry environments, whereas 20.3% of areas with increased resilience were located in moist tropical forests. More intense and prolonged droughts led to a pronounced decline in resilience. Mean annual precipitation was identified as the most important regulator influencing resilience changes after drought, while soil phosphorus was the most consistent regulator across forest biomes, exhibiting widespread mitigating effects on resilience loss. Along decreasing precipitation gradients, the mitigating effect of soil phosphorus on post-drought resilience loss intensified. These findings provide insights into how tropical forests respond to drought and offer practical guidance for region-specific, adaptive forest management under a changing climate. Drought disturbances are reducing the recovery capacity of tropical forests, especially in drier conditions, but soil phosphorus can mitigate this impact, according to a satellite-based analysis of ecosystem resilience.
When soil moisture across all layers of the entire profile is depleted, ecosystems face the highest risk because they lose all vertical buffering capacity against drought. However, these vertically compound soil moisture droughts, in which every soil layer suffers simultaneous water deficits, have been largely ignored because previous monitoring and risk assessments relied on entire-profile mean soil moisture. Here we identify vertically (0–100 cm) compound droughts worldwide during warm seasons of 1981–2020 using multilayer soil moisture products. Their annual duration and ratio have increased across more than half of global lands over the past four decades, with pronounced hotspots in southwestern North America, South America, Africa, mid-latitude Eurasia, southeastern Asia and Australia. Vertically compound droughts cause substantial declines in ecosystem productivity, particularly in forests and croplands, threatening carbon sink stability and food security. By contrast, diagnosing drought solely from entire-profile averages causes an overestimation of vertically compound drought duration by about 128.3% but an underestimation of associated ecosystem losses by about 27.8%. These projections and systematic biases highlight the urgency of developing multilayer monitoring, mitigation and adaptation strategies for vertically compound droughts. Vertically compound soil moisture droughts—when all soil layers are depleted—have intensified worldwide, driving sharper ecosystem losses than single-layer droughts, according to global analyses of multilayer soil moisture.
Global-scale circulation dominates material transport in planetary atmospheres, which is thought to account for large-scale compositional mixing on Earth and other planets. However, observations of the Martian atmosphere challenge this picture. The mixing ratios of dust and gas species (H2O, CO, Ar) show large planetary-scale inhomogeneities, yet the mechanism causing this has been difficult to define. Here we investigate particle transport in the Martian atmosphere using a Lagrangian tracking method based on reanalysis data. We find that the coherent structure of the single-cell Hadley circulation on Mars can produce a distinct material transport pattern. Dynamical barriers prevent material mixing between the inside and outside of the Hadley cell and allow pole-to-pole teleconnection. Dimensional analysis indicates this is caused by the combined effect of rapid planetary rotation and the thin atmosphere of Mars. The dominance of the mean circulation over the eddy transport gives rise to this unique transport regime, which is fundamentally distinct from those on Earth and Venus. This finding challenges the conventional view of material mixing from planetary-scale circulations, suggesting planetary atmospheric dynamics can confine materials and restrict redistribution. Single-cell Hadley circulation drives pole-to-pole connection on Mars but also inhibits material mixing between the cell’s interior and exterior, according to a study of the Martian atmosphere using Lagrangian particle tracking.
China, the world’s largest CO2 emitter, leverages forest area expansion as a strategy to achieve carbon neutrality by the 2060s. However, the respective contribution of reforestation on previously forested land and afforestation on non-forested land, remains uncertain due to limited observational data and the absence of spatially and temporally explicit analyses. Here we used locally derived aboveground biomass accumulation curves for each 1° grid cell and a spatially explicit bookkeeping model to track annual carbon uptake from reforestation and afforestation alongside emissions from forest disturbances. We then estimated the forest carbon balance of China for different forest types at 30 m resolution from 1986 to 2019. Forest biomass carbon sinks averaged 0.139 ± 0.052 PgC yr−1, increasing from 0.1 ± 0.015 PgC yr−1 in the 1990s to 0.2 ± 0.012 PgC yr−1 in the 2010s. Despite afforested tree cover expanding faster (1.31 Mha yr⁻1) than reforestation after disturbance (1.06 Mha yr⁻1), post-disturbance regrowth exhibited a higher growth rate (1.47 ± 0.42 MgC ha−1 yr−1) in carbon sequestration than that of afforestation (0.96 ± 0.28 MgC ha−1 yr−1), making reforestation the dominant contributor to China’s forest carbon sink over the past three decades. The results inform forest carbon accounting and prioritize protecting regrowing forests alongside targeted afforestation to achieve carbon neutrality. Reforestation on previously forested areas after disturbances exhibits higher post-disturbance carbon sequestration than afforestation on previously unforested land, and has dominated China’s forest carbon sink over the past three decades, according to above- and below-ground biomass estimates.
Convection in the subpolar North Atlantic feeds highly oxygenated water into the lower limb of the Atlantic Meridional Overturning Circulation (AMOC), sustaining deep-sea organisms across a vast expanse of the ocean. Yet, the rates and processes responsible for this oxygenation have remained largely hidden by a lack of direct measurements. Here we apply newly developed calibration protocols for multi-year oxygen measurements to quantify oxygen transport across a mooring array spanning the Labrador Sea. The results show that Labrador Sea deep convection results in a substantial export of oxygen to the lower limb of the AMOC. Specifically, local air–sea exchange adds ~4.1 Tmol yr−1 of oxygen to dense Labrador Sea waters, while deep convection moves ~23.5 Tmol yr−1, added to lighter waters upstream in the eastern subpolar North Atlantic, to those same dense waters. We estimate that this export is sufficient to balance biological respiration across much of the deep North Atlantic, making processes in the Labrador Sea critical to North Atlantic oxygenation despite their small contribution to the densification of the AMOC lower limb. This finding shows that future risk of deep North Atlantic deoxygenation depends not only on the processes that drive overturning, but also on Labrador Sea deep convection. The Labrador Sea plays a crucial role in transporting oxygen into the deep limb of the Atlantic Meridional Overturning Circulation, despite its limited contribution to density transformation, according to an analysis of 2 years of mooring data.
Global warming is reorganizing atmospheric circulation and hydroclimate, and tropical rainfall is a key manifestation of this response. Yet how these large-scale changes are translated into the tropical rainfall seasonal cycle remains uncertain because organized convection, which produces a large fraction of tropical rainfall and often occurs in mesoscale convective systems, is poorly represented in conventional climate models. Here we use decade-long global simulations with a high-resolution Earth system model coupled to a multiscale modelling framework that explicitly represents deep convection to quantify the role of mesoscale convective systems in future rainfall seasonality. We find that mesoscale convective systems would dominate the future changes in both the amplitude and phase of tropical precipitation seasonal cycle. Under a high-emission scenario, the seasonal cycle of precipitation from mesoscale convective systems is amplified by 38–45% and delayed by 10–15 days, exceeding the corresponding changes in mean tropical precipitation. The delay arises from fewer early season mesoscale convective systems associated with slower seasonal migration of the Hadley cell, whereas amplification is driven mainly by increased rainfall intensity within these systems. These results indicate that organized convection is a major pathway through which warming reshapes tropical rainfall seasonality, affecting the timing and intensity of hydroclimate risks. High-resolution simulations project that the seasonal cycle of precipitation from mesoscale convective systems will intensify by 38–45% and be delayed by 10–15 days under high emissions, driving future changes in tropical rainfall seasonality.
Renewable energy droughts, characterized by prolonged periods of low winds and reduced solar irradiance, threaten the stability of electricity supply, with fossil fuel plants expected to cover much of the energy deficit. By integrating an electricity system model with a chemical transport model, here we quantify the effects of fossil fuel plant emissions on China’s air quality in the 2050s during renewable energy droughts. Our findings reveal that under scenarios of high renewable penetration, even with the best pollution-control technologies, fossil fuel plant emissions can boost PM2.5 by 15–40% and O3 by 10–20% during renewable energy shortages, raising the frequency of extreme pollution hours by 40–100% annually. Attribution analysis indicates that more stagnant weather and elevated pollutant emissions from fossil fuel plants contribute comparably to extreme pollution during renewable energy droughts. Incorporating health costs of elevated pollution into renewable capacity planning could reduce reliance on fossil fuel generation by ~50% in China by 2050, enabling a deeper clean energy transition. Integrated model simulations suggest that air quality across China could be substantially degraded by emissions from fossil fuel power plants during renewable energy droughts in the 2050s, underscoring the need for a deeper clean energy transition.
Snow cover serves as a critical component of cold deserts, providing a sustained source of available water over time. Biocrusts largely cover soils in deserts, yet their role in regulating snowpack ablation remains largely unknown. Here we conducted a multiyear, in situ and continuous experiment to evaluate the effects of moss-dominated biocrusts on the depth and duration of snow cover, along with their consequences for soil moisture, microbial richness (bacteria and fungi) and soil respiration (carbon efflux). Compared with bare soil, our long-term measurements revealed that moss biocrusts greatly extended snow cover duration by 20.1% (65 h) and enhanced mean snow depth by 27.1%. These effects were associated with the influences of biocrusts on surface roughness and thermal conductivity, which further contributed to greater snowmelt, leading to 16.0% higher water content and up to a 46.1% increase in microbial richness beneath biocrusts compared with nearby bare soils. Furthermore, soil carbon efflux driven by microbial respiration was up to 33.5% higher under biocrusts compared with bare soils. Our study suggests that moss biocrusts play an important role in supporting biological activity and ecosystem function in cold deserts under global warming by moderating snow cover dynamics. Long-term soil biogeochemical measurements in a cold desert in China suggest that moss biocrusts can substantially extend snow cover duration and increase snow depth during snow events, thereby sustaining soil biological activity and ecosystem function under a warming climate.
During Pleistocene ice ages, abrupt climate changes co-occurred with switches in Atlantic Meridional Overturning Circulation (AMOC) strength. The global impact and characteristic north–south temperature pattern of these events is typically explained via interhemispheric redistribution of heat in a conceptual framework called the ‘thermal bipolar seesaw’. Here we synthesize recent work on an emerging alternative framework centred instead on the global ocean heat content and planetary energy budget, which we illustrate using simulations of spontaneous abrupt climate change in three climate models. The strong and weak AMOC modes are associated with oceanic and planetary heat loss and heat gain, respectively, facilitated via changes to North Atlantic deep convection and radiative feedbacks that set the top-of-the-atmosphere energy budget. Antarctic and Greenland temperatures, as recorded in ice cores, reflect ocean heat content and the rate of North Atlantic heat loss, respectively. Climate instability at intermediate glacial states reflects an inability to balance global ocean heat uptake with North Atlantic heat loss for either of the two AMOC modes. Our synthesis suggests that the AMOC strength acts as a ‘heat valve’ that alters planetary temperature by changing the radiative balance. This implies amplified planetary heat uptake in response to projected future AMOC weakening. Variations in Atlantic Meridional Overturning Circulation strength through abrupt Dansgaard–Oeschger events during Pleistocene glacial periods controlled ocean heat content, and heat uptake by the planet as a whole, according to a synthesis of simulations.
Humble hydromagnesite is a hydrated carbonate with outsized importance. Yongjie Lin and Ian Power explore its potential for both carbon sequestration and unlocking the secrets of potential past microbial life on Mars.
The European Union’s climate goals rely on forests as carbon sinks. Remote sensing data reveal accelerating biomass loss and distinguish the contributions of harvesting and natural disturbances, helping to better inform forest policy and climate actions.
