Climate Feedbacks Research Articles

Microplastic pollution promotes soil respiration: A global-scale meta-analysis.

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

Impact of three decades of warming, increased nutrient availability, and increased cloudiness on the fluxes of greenhouse gases and biogenic volatile organic compounds in a subarctic tundra heath.

Climate change is exposing subarctic ecosystems to higher temperatures, increased nutrient availability, and increasing cloud cover. In this study, we assessed how these factors affect the fluxes of greenhouse gases (GHGs) (i.e., methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2)), and biogenic volatile organic compounds (BVOCs) in a subarctic mesic heath subjected to 34 years of climate change related manipulations of temperature, nutrient availability, and light. GHGs were sampled from static chambers and gases analyzed with gas chromatograph. BVOCs were measured using the push-pull method and gases analyzed with chromatography-mass spectrometry. The soil temperature and moisture content in the warmed and shaded plots did not differ significantly from that in the controls during GHG and BVOC measurements. Also, the enclosure temperatures during BVOC measurements in the warmed and shaded plots did not differ significantly from temperatures in the controls. Hence, this allowed for assessment of long-term effects of the climate treatment manipulations without interference of temperature and moisture differences at the time of measurements. Warming enhanced CH4 uptake and the emissions of CO2, N2O, and isoprene. Increased nutrient availability increased the emissions of CO2 and N2O but caused no significant changes in the fluxes of CH4 and BVOCs. Shading (simulating increased cloudiness) enhanced CH4 uptake but caused no significant changes in the fluxes of other gases compared to the controls. The results show that climate warming and increased cloudiness will enhance CH4 sink strength of subarctic mesic heath ecosystems, providing negative climate feedback, while climate warming and enhanced nutrient availability will provide positive climate feedback through increased emissions of CO2 and N2O. Climate warming will also indirectly, through vegetation changes, increase the amount of carbon lost as isoprene from subarctic ecosystems.

Microbial Communities Degrade Ancient Permafrost‐Derived Organic Matter in Arctic Seawater

AbstractThe Arctic is experiencing rapid warming, which among other processes results in increasing erosion of coastal permafrost and the release of ancient organic carbon (OC) into the Arctic Ocean, which in turn might result in greenhouse gas emissions following its decomposition. Supply of terrigenous organic matter to the ocean affects near‐shore nutrient concentrations and the composition of microbial communities—highlighting the need to understand the fate of permafrost‐derived carbon in this fragile ecosystem. We incubated material from coastal Yedoma permafrost for 85 days in seawater collected during the Arctic Century expedition. During this experiment, 2.8 ± 1.4% of OC from coastal Yedoma was respired to CO2. Radiocarbon analysis revealed that 88 ± 15% of the released CO2 originated from ancient material (∼40,000 years), indicating that degradation of permafrost OC reintroduces old carbon into the short‐term carbon cycle. Hence, the permafrost climate feedback may be enhanced in the coming decades when coastal erosion accelerates. Additionally, 0.9 ± 0.3% of Yedoma OC was leached as dissolved OC. The observed net production of inorganic nitrogen during the incubation could potentially provide a negative feedback by stimulating primary production. Bacterial community analysis showed a succession of primary responders to biolabile substrates (e.g., Psychrobacter and Colwellia) followed by secondary consumers of less biolabile substrates (e.g., Maribacter and Pseudohongiella), plus a potential establishment of permafrost associated‐bacteria on particles. Overall, our data show that OC input from thawing permafrost stimulates bacterial dynamics, with likely implications for regional biogeochemical cycles and the Earth's climate.

Toward User-Friendly All-Sky Surface Longwave Downward Radiation from Space: General Scheme and Product

Abstract Longwave downward radiation (LWDR) is an important driving parameter in climate and hydrological models. Compared to traditional ground-based measurements, remote sensing has unique advantages in estimating global LWDR. However, for current remote sensing missions, as the typical available satellite-derived LWDR product with global coverage and hourly temporal resolution, the Clouds and the Earth’s Radiant Energy System-Synoptic (CERES-SYN) top of atmosphere and surface fluxes and clouds has a low spatial resolution (1° × 1°). There is still much room for improvement of the existing remote sensing LWDR products in terms of accuracy, spatiotemporal resolutions, and the ability to explain and quantify the changes of longwave radiation at various scales. To overcome these limitations, this paper developed a new global LWDR product with improved accuracy (RMSE < 30 W m−2 over the globe), high temporal resolution (hourly), and spatial resolution (5 km) based on Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. It serves as a LWDR product within the Long-term Earth System spatiotemporally Seamless Radiation budget dataset (referred to as LessRad). As the first long-term high-resolution, spatiotemporally continuous LWDR product (2002–22, 1 h, 5 km), the LessRad reveals its advantages in studying the spatiotemporal variability of LWDR on finer scales. It also provides a valuable data source for various applications, such as analyzing land–atmosphere interactions and quantifying climate feedback, and thus is potentially helpful for understanding Earth’s energy budget and dynamics.

Microbial dynamics in rapidly transforming Arctic proglacial landscapes

Arctic glacial environments are rapidly changing, as the Arctic warms at a rate three to four times faster than the global average (the phenomenon known as Arctic amplification). Microorganisms are uniquely adapted to extreme glacial environments and studying how ecological and climatic feedback loops affect the diversity of these communities is crucial to the characterisation of vulnerable Arctic habitats. Glacial landscapes span a wide range of habitats, from glacier ice to marine waters, and encompass terrestrial, aquatic, and interzonal systems. While glacier shrinkage has been the focus of scientific attention, auxiliary habitats are also impacted by rapid glacier retreat. Auxiliary habitats include terrestrial systems, such as outwash plains, vegetated periglacial environments, and aquatic systems, such as glacier-fed streams, lakes, and glacier-adjacent marine environments. Glacier recession drives high-impact changes in glacier-associated habitats: rising temperatures, increased light penetration of glacial streams, changes in nitrogen-to-phosphate ratios, and increases in availability of glacier-derived organic compounds. In turn, microbial systems in these habitats may experience changes in nutrient dynamics and shifts in community structures. The exposure of new lands by retreating glaciers may also result in increased dust and microbial dispersal into the atmosphere. Here, we discuss the effects of climate change on glacial microbiomes and the feedback loops between microbial community dynamics and the large-scale climatic processes in the Arctic. We characterise aspects of vulnerable microbial ecosystems and highlight the importance of preserving unseen microbial biodiversity. We then outline current capacities for microbial conservation, focusing on cryopreservation and biobanking. Lastly, we suggest future research directions and steps that academic and governmental institutions may take to foster research and collaboration with Indigenous communities.

Profile distribution and edaphic controls of soil organic carbon in dominant soil orders of Chitwan, Nepal

Soil profile distribution of soil organic carbon (SOC) in different soil types provides information about the carbon (C) dynamics in terrestrial ecosystems, and is also important for understanding climate feedback mechanisms and for developing a proper farm level SOC management decision. However, there are limited studies on it when we consider soil horizons of dominant soil orders of Nepal, which mostly use a fixed depth approach rather than horizon-based approach while studying profile SOC distribution. We collected soils from master horizons (0 to 100 cm) of three dominant soil orders (Alfisols, Entisols, and Inceptisols) in Chitwan district of Nepal, to understand the controlling factors of SOC accumulation. Dominant soil order regions were identified using a soil map prepared by the National Land Use Planning Project where a pit of 1 m3 was dug for each soil order and replicated four times. The highest SOC concentration (10.1 ± 0.6 g kg−1) was found in Alfisols followed by Entisols (8.8 ± 0.3 g kg−1) and Inceptisols (7.2 ± 8.9 g kg−1). Similarly, the highest SOC stock was found in the soil profile of Alfisols (200.01 ± 15.97 t ha−1) followed by Entisols (124.67 ± 12.20 t ha−1) and Inceptisols (113.27 ± 10.30 t ha−1) horizons. Surface (A) horizons of all three-soil order had significantly higher SOC than sub-surface (B and C) horizons. Regression analysis showed significant variability in SOC to clay content (R2 = 0.45, p < 0.0001), sand (R2 = 0.19, p < 0.001), and total nitrogen (N; R2 = 0.835, p < 0.001). Principal component analysis showed that the controlling edaphic factors differ with the soil types considering SOC change in the whole soil profile. Overall, we found that soil pH, N, clay and sand contents are the major controlling factors that drive the SOC accrual in dominant soil orders of Nepal.Graphical

Nanocluster Aerosols from Ozone-Human Chemistry Are Dominated by Squalene-Ozone Reactions.

Nanocluster aerosols (NCAs, <3 nm particles) are associated with climate feedbacks and potentially with human health. Our recent study revealed NCA formation owing to the reaction of ozone with human surfaces. However, the underlying mechanisms driving NCA emissions remain unexplored. Squalene is the most abundant compound in human skin lipids that reacts with ozone, followed by unsaturated fatty acids. This study aims to examine the contribution of the squalene-ozone reaction to NCA formation and the influence of ozone and ammonia (NH3) levels. In a climate-controlled chamber, we painted squalene and 6-hexadecenoic acid (C16:1n6) on glass plates to facilitate their reactions with ozone. The squalene-ozone reaction was further investigated at different ozone levels (15 and 90 ppb) and NH3 levels (0 and 375 ppb). The results demonstrate that the ozonolysis of human skin lipid compounds contributes to NCA formation. With a typical squalene-C16:1n6 ratio found in human skin lipids (4:1), squalene generated 40 times more NCAs than did C16:1n6 and, thus, dominated NCA formation. More NCAs were generated with increased ozone levels, whereas increased NH3 levels were associated with the stronger generation of larger NCAs but fewer of the smallest ones. This study experimentally confirms that NCAs are primarily formed from squalene-ozone reactions in ozone-human chemistry.

Ebullition dominates methane emissions in stratified coastal waters

Coastal areas are an important source of methane (CH4). However, the exact origins of CH4 in the surface waters of coastal regions, which in turn drive sea-air emissions, remain uncertain. To gain a comprehensive understanding of the current and future climate change feedbacks, it is crucial to identify these CH4 sources and processes that regulate its formation and oxidation. This study investigated coastal CH4 dynamics by comparing water column data from six stations located in the brackish Tvärminne Archipelago, Baltic Sea. The sediment biogeochemistry and microbiology were further investigated at two stations (i.e., nearshore and offshore). These stations differed in terms of stratification, bottom water redox conditions, and organic matter loading. At the nearshore station, CH4 diffusion from the sediment into the water column was negligible, because nearly all CH4 was oxidized within the upper sediment column before reaching the sediment surface. On the other hand, at the offshore station, there was significant benthic diffusion of CH4, albeit the majority underwent oxidation before reaching the sediment-water interface, due to shoaling of the sulfate methane transition zone (SMTZ). The potential contribution of CH4 production in the water column was evaluated and was found to be negligible. After examining the isotopic signatures of δ13C-CH4 across the sediment and water column, it became apparent that the surface water δ13C-CH4 values observed in areas with thermal stratification could not be explained by diffusion, advective fluxes, nor production in the water column. In fact, these values bore a remarkable resemblance to those detected below the SMTZ. This supports the hypothesis that the source of CH4 in surface waters is more likely to originate from ebullition than diffusion in stratified brackish coastal systems.

Competing climate feedbacks of ice sheet freshwater discharge in a warming world

Freshwater discharge from ice sheets induces surface atmospheric cooling and subsurface ocean warming, which are associated with negative and positive feedbacks respectively. However, uncertainties persist regarding these feedbacks’ relative strength and combined effect. Here we assess associated feedbacks in a coupled ice sheet-climate model, and show that for the Antarctic Ice Sheet the positive feedback dominates in moderate future warming scenarios and in the early stage of ice sheet retreat, but is overwhelmed by the negative feedback in intensive warming scenarios when the West Antarctic Ice Sheet undergoes catastrophic collapse. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both the Greenland and the Antarctic ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet’s retreat via the Bipolar Seesaw. These results highlight the crucial role of ice sheet-climate interactions via freshwater flux in future ice sheet retreat and associated sea-level rise.

Evaluation of the RegCM model capability in simulating leaf area index and climatic feedback of dynamic vegetation cover in Iran

Evaluation of the RegCM model capability in simulating leaf area index and climatic feedback of dynamic vegetation cover in Iran

Fungi and bacteria trade-off mediates drought-induced reduction in wood decomposition

Climate change has significantly increased the frequency and intensity of drought events in recent decades, which may affect the decomposition of organic matter such as deadwood. Previous studies have examined the impacts of microclimate and wood traits on deadwood decomposition, but how wood microbes regulate effects of drought intensity on deadwood decomposition remains unclear. In this study, a field drought experiment was conducted with three throughfall exclusion levels (i.e., control, −35% and −70% rainfall treatments) in a subtropical forest to probe relative importance of microclimate, wood traits, and microbial biomass on wood decomposition. Our results showed that the −35% and −70% rainfall treatments significantly decreased wood CO2 efflux by 28.27% and 47.49%, respectively. Drought-induced decreases in wood CO2 efflux were mainly mediated by wood microbial biomass, particularly wood fungi biomass. The structural equation modelling indicated a shift in the dominant wood microbial communities in regulating wood CO2 efflux from bacteria to fungi as drought intensities increased. Our findings highlight the crucial role of wood microbial community with the trade-off between fungi and bacteria on deadwood decomposition under drought, which should be taken into account to decode forest carbon cycle − climate feedback in the future research.

Time-series simulation of alpine grassland cover using transferable stacking deep learning and multisource remote sensing data in the Google Earth Engine

The growth of vegetation on the Qinghai Tibet Plateau (QTP) is experiencing significant changes due to climate change. There is still a lack of high-precision simulation methods for alpine grassland cover (AGC), and the climate feedback mechanisms of AGC remain unclear, which poses challenges for the production of high-precision AGC products and the formulation of ecological conservation policies. In this study, a transferable stacking deep learning (Stacking-DL) model is proposed based on a CNN, a DNN, and a GRU for AGC time series simulation. The applicability of deep learning models for AGC simulation is evaluated based on long time series of measured data, MODIS data, and environmental factors. Finally, the AGC spatiotemporal changes and controlling environmental factors in the alpine region were analyzed based on Sen’s slope and structural equation modeling (SEM). The results showed that feature selection and parameter optimization improved the applicability of the deep learning models in AGC simulations, and the DNN (R2 = 0.899, RMSE = 0.078) model performed best among the base deep learning models. The Stacking-DL model combines the advantages of multiple models and achieves high transfer accuracy. In the YRSR, the AGC increase area (20.34 %) is greater than the AGC decrease area (3.34 %), the increase area is mainly located in the northeast, and the decrease area is mainly located in the southwest. AGC changes in the YRSR are mainly controlled by permafrost and climate. This study provides a high-precision and transferable vegetation monitoring model for alpine mountain regions based on advanced deep learning models and clarifies the response mechanism of AGC under climate change.

Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η). Here, we analyzed η values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in η for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on η over the past 27 y. Soil moisture was found to modulate the sensitivity of η to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback.

Randomized trial of the leadership and organizational change for implementation (LOCI) strategy in substance use treatment clinics

IntroductionEvidence-based practice (EBP) implementation represents a strategic change that requires alignment of leadership and support throughout organizations. Leadership and Organizational Change for Implementation (LOCI) is a multifaceted implementation strategy that aims to improve implementation leadership and climate within organizations through iterative cycles of leadership and climate assessment and feedback, leadership training and coaching, and strategic planning with upper-level leaders. This study tested the effects of LOCI on transformational and implementation leadership, implementation climate, implementation citizenship behavior, and EBP reach. MethodsA multiple cohort, cluster randomized trial tests the effect of LOCI in 60 clinics across nine behavioral health organizations in California and Arizona, USA. The study randomized clinics within organizations to either LOCI or a leadership training webinar control condition in three consecutive cohorts. Repeated web-based surveys of direct service providers (nLOCI = 201, nControl = 179) assessed leadership, implementation climate, and implementation citizenship over time. Multilevel autoregressive modeling was the primary statistical analysis such that providers (level-1) were nested within clinics (level-2). The study predicted between-condition differences at 4-, 8-, and 12-month follow-up assessments. Provider engagement in a fidelity monitoring process assessed reach of motivational interviewing (i.e., number of sessions recorded/submitted for fidelity coding). An independent sample t-test explored between condition differences in motivational interviewing reach. ResultsResults indicated between condition differences at 4 months for implementation leadership, implementation climate, and implementation citizenship behavior such that greater improvements were evidenced in the LOCI condition compared to the control condition. Reach of MI was significantly greater in the LOCI vs control condition such that LOCI providers were significantly more likely to engage in the fidelity monitoring process (chi-square (1, n = 370) = 5.59, p = .018). ConclusionsLOCI was developed based on organizational theories of strategic leadership and climate to affect organizational change processes that communicate that innovation implementation is expected, supported, and recognized as a value of the organization. The LOCI implementation strategy resulted in more positive hypothesized outcomes compared to the control condition. Organizational change strategies have utility for implementing health innovations in complex, multilevel contexts and for greater sustainment of facilitative leader behaviors, strategic implementation climate, and improved implementation outcomes. Trial registrationThis study is registered with Clinicaltrials.gov gov (NCT03042832, 2 February 2017; retrospectively registered).

Vegetation greening amplifies shallow soil temperature warming on the Tibetan Plateau

Vegetation changes are expected to alter soil thermal regimes, consequently modifying climate feedbacks related to frozen ground thawing and carbon cycling in cold regions. The Tibetan Plateau (TP) contains diverse alpine ecosystems and the largest area of frozen ground in low–mid latitude regions. Evidence suggests ongoing vegetation greening and permafrost degradation during the past several decades on the TP. However, the effect of vegetation changes on soil thermal regimes on the TP is not well understood. Here, we quantify the response of shallow soil temperature change to vegetation greening on the TP using remote–sensing data, in–situ observations, and physics–based modelling. Our results show that over the past 20 years, vegetation greening on the TP was accompanied a notable decrease in the area of bare land by approximately 0.7% (5000 km2). Annual mean soil temperature showed a significant warming trend of 0.57 °C decade–1 (p < 0.05) during the period 1983–2019, exceeding the warming rate of surface air temperature. Changes in vegetation resulted in a warming effect on annual shallow soil temperature of 0.15 ± 0.33 °C across the TP during the period 2000–2019. The warming effect varies with frozen soil types: 0.24 ± 0.48 °C in permafrost, 0.18 ± 0.36 °C in seasonally frozen ground, and 0.11 ± 0.32 °C in unfrozen ground. The net warming effect was caused by a decrease in albedo and increase in radiation penetrating the canopy, outweighing the cooling effect related to a limited increase in evapotranspiration.

Energy Gain Kernel for Climate Feedbacks. Part I: Formulation and Physical Understanding

Abstract This paper introduces a climate feedback kernel, referred to as the “energy gain kernel” (EGK). EGK allows for separating the net longwave radiative energy perturbations given by a Planck feedback matrix explicitly into thermal energy emission perturbations of individual layers and thermal radiative energy flux convergence perturbations at individual layers resulting from the coupled atmosphere–surface temperature changes in response to the unit forcing in individual layers. The former is represented by the diagonal matrix of a Planck feedback matrix and the latter by EGK. Elements of EGK are all positive, representing amplified energy perturbations at a layer where forcing is imposed and energy gained at other layers, both of which are achieved through radiative thermal coupling within an atmosphere–surface column. Applying EGK to input energy perturbations, whether external or internal due to responses of nontemperature feedback processes to external energy perturbations, such as water vapor and albedo feedbacks, yields their total energy perturbations amplified through radiative thermal coupling within an atmosphere–surface column. As the strength of EGK depends exclusively on climate mean states, it offers a solution for effectively and objectively separating control climate state information from climate perturbations for climate feedback studies. Given that an EGK comprises critical climate mean state information on mean temperature, water vapor, clouds, and surface pressure, we envision that the diversity of EGK across different climate models could provide insight into the inquiry of why, under the same anthropogenic greenhouse gas increase scenario, different models yield varying degrees of global mean surface warming. Significance Statement The wide range of 2.5°–4.0°C in global warming projections by climate models hinders our ability to predict its impacts. The newly introduced energy gain kernel (EGK) provides critical information for climate mean infrared opacity, which is collectively determined by climate mean temperature, water vapor, clouds, and surface pressure fields. EGK is directly derived from physical principles without additional definition. EGK captures the temperature feedback’s amplification of energy perturbations initiated from both external forcing and internal nontemperature feedback processes. EGK allows for disentangling positive and negative aspects of temperature feedback, rectifying the common misconception in existing temperature kernels that portray temperature feedback as predominantly negative. The diversity of EGK across different climate models may help explain their varying global warming degrees.

Is our understanding of aquatic ecosystems sufficient to quantify ecologically driven climate feedbacks?

The Earth functions as an integrated system-its current habitability to complex life is an emergent property dependent on interactions among biological, chemical, and physical components. As global warming affects ecosystem structure and function, so too will the biosphere affect climate by altering atmospheric gas composition and planetary albedo. Constraining these ecosystem-climate feedbacks is essential to accurately predict future change and develop mitigation strategies; however, the interplay among ecosystem processes complicates the assessment of their impact. Here, we explore the state-of-knowledge on how ecological and biological processes (e.g., competition, trophic interactions, metabolism, and adaptation) affect the directionality and magnitude of feedbacks between ecosystems and climate, using illustrative examples from the aquatic sphere. We argue that, despite ample evidence for the likely significance of many, our present understanding of the combinatorial effects of ecosystem dynamics precludes the robust quantification of most ecologically driven climate feedbacks. Constraining these effects must be prioritized within the ecological sciences for only by studying the biosphere as both subject and arbiter of global climate can we develop a sufficiently holistic view of the Earth system to accurately predict Earth's future and unravel its past.

Positive feedbacks and alternative stable states in forest leaf types

The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks.

How Does Plant CO2 Physiological Forcing Amplify Amazon Warming in CMIP6 Earth System Models?

AbstractThe physiological response to increasing CO2 concentrations will lead to land surface warming through a redistribution of the energy balance. As the Amazon is one of the most plant‐rich regions, the increase in surface temperature, caused by plant CO2 physiological forcing, is particularly large compared to other regions. In this study, we analyze the outputs of the 11 models in the Coupled Model Intercomparison Project Phase 6 to find out how CO2 physiological forcing amplifies Amazonian warming under elevated CO2 levels. With the CO2 concentration increase from 285 to 823 ppm, the Amazon temperature increased by 0.48 ± 0.42 K as a result of plant physiological forcing. Moreover, we assess the contributions of each climate feedback to the surface warming due to physiological forcing by quantifying climate feedbacks based on radiative kernels. Lapse rate feedback and cloud feedback, analyzed as the primary contributors, accounted for 53% and 37% of Amazon warming, respectively. The warming contributions of these two feedbacks also exhibit a significant spread, which contributes to the predictive uncertainty. The surface warming due to reduced evapotranspiration is larger than the upper tropospheric warming in the Amazon, resulting in surface warming by lapse rate feedback. In addition, cloud cover in the Amazon region decreases due to the reduced evapotranspiration. Decreased cloud cover amplifies surface warming through the shortwave cloud feedback. Furthermore, differences in circulation and local convection caused by physiological effect contribute to the inter‐model spread of the cloud feedback.

TEOS-10 Equations for Determining the Lifted Condensation Level (LCL) and Climatic Feedback of Marine Clouds

At an energy flux imbalance of about 1 W m−2, the ocean stores 90% of the heat accumulating by global warming. However, neither the causes of this nor the responsible geophysical processes are sufficiently well understood. More detailed investigations of the different phenomena contributing to the oceanic energy balance are warranted. Here, the role of low-level marine clouds in the air–sea interaction is analysed. TEOS-10, the International Thermodynamic Equation of State of Seawater—2010, is exploited for a rigorous thermodynamic description of the climatic trends in the lifted condensation level (LCL) of the marine troposphere. Rising sea surface temperature (SST) at a constant relative humidity (RH) is elevating marine clouds, cooling the cloud base, and reducing downward thermal radiation. This LCL feedback effect is negative and counteracts ocean warming. At the current global mean SST of about 292 K, the net radiative heat flux from the ocean surface to the LCL cloud base is estimated to be 24 W m−2. Per degree of SST increase, this net flux is expected to be enhanced by almost 0.5 W m−2. The climatic LCL feedback effect is relevant for the ocean’s energy balance and may be rigorously thermodynamically modelled in terms of TEOS-10 equations. LCL height may serve as a remotely measured, sensitive estimate for the sea surface’s relative fugacity, or conventional relative humidity.