1,003 research outputs found
Assessment of the impacts of biological nitrogen fixation structural uncertainty in CMIP6 earth system models
Biological nitrogen fixation is the main source of new
nitrogen into natural terrestrial ecosystems and consequently in the
nitrogen cycle in many earth system models. Representation of biological
nitrogen fixation varies, and because of the tight coupling between the
carbon and nitrogen cycles, previous studies have shown that this affects
projected changes in net primary productivity. Here we present the first
assessment of the performance of biological nitrogen fixation in models
contributing to CMIP6 compared to observed and observation-constrained
estimates of biological nitrogen fixation. We find that 9 out of 10 models
represent global total biological nitrogen fixation within the uncertainty
in recent global estimates. However, 6 out of 10 models overestimate the amount of fixation in the tropics and therefore the extent of the latitudinal
gradient in the global distribution. For the SSP3-7.0 scenario of future
climate change, models project increases in fixation over the 21st century of up to 80 %. However, while the historical range of biological
nitrogen fixation amongst models is large (up to 140 kg N ha−1 yr−1 at the grid cell level and 43–208 Tg N yr−1 globally) this does not have explanatory power for variations within the model ensemble of
net primary productivity or the coupled nitrogen–carbon cycle. Models with
shared structures can have significant variations in both biological
nitrogen fixation and other parts of the nitrogen cycle without differing in
their net primary productivity. This points to systematic challenges in the
representation of carbon–nitrogen model structures and the severe
limitations of models using net primary productivity or evapotranspiration
to project the biological nitrogen fixation response to elevated atmospheric
carbon dioxide or other environmental changes.</p
The global distribution of biological nitrogen fixation in terrestrial natural ecosystems
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordAccompanying data is available from dataset in ORE via the link in this record - https://doi.org/10.24378/exe.2063Biological nitrogen fixation is a key contributor to sustaining the terrestrial carbon cycle, providing nitrogen input that plants require. However, the amount and global distribution of this fixation is highly disputed. Using a comprehensive meta-analysis of field measurements, we make a new assessment of global biological nitrogen fixation (BNF). We assessed the relationship between BNF in natural terrestrial environments and empirical predictors of BNF commonly used in terrestrial ecosystem and earth system models. We found no evidence for any statistically significant relationship between BNF and evapotranspiration and net or gross primary terrestrial productivity. We assessed the relationship between BNF and 11 other climate variables and soil properties at a global scale. We found that all the variables we considered had little predictive power for BNF. Using averaged biome values upscaled we calculated the median global inputs of BNF in natural ecosystems as 88 Tg N year−1. The range (52–130 Tg N year−1) encompasses most recent estimates and broadly agrees with recent independent top-down estimates of BNF. The global values indicate a significant role for free living, as opposed to symbiotic, BNF, accounting for at least a third of all BNF. This work provides a new global benchmark and spatial distribution data set of BNF using a bottom-up methodology.European Commissio
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Quantifying the relative importance of land cover change from climate and land use in the representative concentration pathways
Climate change is projected to cause substantial alterations in vegetation distribution, but these have been given little attention in comparison to land-use in the Representative Concentration Pathway (RCP) scenarios. Here we assess the climate-induced land cover changes (CILCC) in the RCPs, and compare them to land-use land cover change (LULCC). To do this, we use an ensemble of simulations with and without LULCC in earth system model HadGEM2-ES for RCP2.6, RCP4.5 and RCP8.5. We find that climate change causes an expansion poleward of vegetation that affects more land area than LULCC in all of the RCPs considered here. The terrestrial carbon changes from CILCC are also larger than for LULCC. When considering only forest, the LULCC is larger, but the CILCC is highly variable with the overall radiative forcing of the scenario. The CILCC forest increase compensates 90% of the global anthropogenic deforestation by 2100 in RCP8.5, but just 3% in RCP2.6. Overall, bigger land cover changes tend to originate from LULCC in the shorter term or lower radiative forcing scenarios, and from CILCC in the longer term and higher radiative forcing scenarios. The extent to which CILCC could compensate for LULCC raises difficult questions regarding global forest and biodiversity offsetting, especially at different timescales. This research shows the importance of considering the relative size of CILCC to LULCC, especially with regard to the ecological effects of the different RCPs
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Full effects of land use change in the representative concentration pathways
Future land use change (LUC) is an important component of the IPCC representative concentration pathways (RCPs), but in these scenarios' radiative forcing targets the climate impact of LUC only includes greenhouse gases. However, climate effects due to physical changes of the land surface can be as large. Here we show the critical importance of including non-carbon impacts of LUC when considering the RCPs. Using an ensemble of climate model simulations with and without LUC, we show that the net climate effect is very different from the carbon-only effect. Despite opposite signs of LUC, all the RCPs assessed here have a small net warming from LUC because of varying biogeophysical effects, and in RCP4.5 the warming is outside of the expected variability. The afforestation in RCP4.5 decreases surface albedo, making the net global temperature anomaly over land around five times larger than RCPs 2.6 and 8.5, for around twice the amount of LUC. Consequent changes to circulation in RCP4.5 in turn reduce Arctic sea ice cover. The small net positive temperature effect from LUC could make RCP4.5's universal carbon tax, which incentivizes retaining and growing forest, counter productive with respect to climate. However, there are spatial differences in the balance of impacts, and potential climate gains would need to be assessed against other environmental aims
Future fire risk under climate change and deforestation scenarios in tropical Borneo
This is the final version. Available from IOP Publishing via the DOI in this record. Data availability statement:
The data that support the findings of this study are
available upon reasonable request from the authors.Fire in the tropical peatland forests of Borneo is an environmental issue with interactions with climate change and deforestation, and the consequences have local and global implications. While research has shown that fire severity and frequency are expected to increase with climate change, there is conflicting model and observational data as to the effect of deforestation on precipitation, which is a key metric for fire risk. To better understand the changes in fire risk from deforestation and climate change we ran simulations of the climate scenario RCP8.5 with and without total deforestation using regional climate model RegCM4. The output was then used for calculations of the Fire Weather Index. We find that annual temperature change from deforestation at elevations above 500m is 53% of the change over the 21st Century in RCP8.5. Fire risk is significantly affected by both climate change and deforestation, despite some increases in precipitation from deforestation. While the multi model dry season (June-August) mean increases in fire risk are larger from elevated atmospheric carbon dioxide, the increases in maximum fire risk are larger from deforestation. The altitude is a good predictor of fire risk change, with larger increases at more densely populated lower elevations where the peatlands are concentrated and smaller increases at higher elevations. Therefore, while deforestation generally causes a smaller increase in climate-related fire risk than climate change, its local control and heterogeneous effects compared to global carbon emissions makes it critical for climate mitigation policy. These high-resolution simulations provide a guide to the most vulnerable areas of Borneo from climatic increases in fire risk.Natural Environment Research Council (NERC
Prediction and measurement of the size-dependent stability of fluorescence in diamond over the entire nanoscale
Fluorescent defects in non-cytotoxic diamond nanoparticles are candidates for
qubits in quantum computing, optical labels in biomedical imaging and sensors
in magnetometry. For each application these defects need to be optically and
thermodynamically stable, and included in individual particles at suitable
concentrations (singly or in large numbers). In this letter, we combine
simulations, theory and experiment to provide the first comprehensive and
generic prediction of the size, temperature and nitrogen-concentration
dependent stability of optically active NV defects in nanodiamonds.Comment: Published in Nano Letters August 2009 24 pages, 6 figure
Quantifying the uncertainty in CME kinematics derived from geometric modeling of heliospheric imager data
Geometric modeling of Coronal Mass Ejections (CMEs) is a widely used tool for assessing their kinematic evolution. Furthermore, techniques based on geometric modeling, such as ELEvoHI, are being developed into forecast tools for space weather prediction. These models assume that solar wind structure does not affect the evolution of the CME, which is an unquantified source of uncertainty. We use a large number of Cone CME simulations with the HUXt solar wind model to quantify the scale of uncertainty introduced into geometric modeling and the ELEvoHI CME arrival times by solar wind structure. We produce a database of simulations, representing an average, a fast, and an extreme CME scenario, each independently propagating through 100 different ambient solar wind environments. Synthetic heliospheric imager observations of these simulations are then used with a range of geometric models to estimate the CME kinematics. The errors of geometric modeling depend on the location of the observer, but do not seem to depend on the CME scenario. In general, geometric models are biased towards predicting CME apex distances that are larger than the true value. For these CME scenarios, geometric modeling errors are minimised for an observer in the L5 region. Furthermore, geometric modeling errors increase with the level of solar wind structure in the path of the CME. The ELEvoHI arrival time errors are minimised for an observer in the L5 region, with mean absolute arrival time errors of 8.2 ± 1.2 h, 8.3 ± 1.0 h, and 5.8 ± 0.9 h for the average, fast, and extreme CME scenarios
Unusual Subpulse Modulation in PSR B0320+39
We report on an analysis of the drifting subpulses of PSR B0320+39 that
indicates a sudden step of ~180 degrees in subpulse phase near the centre of
the pulse profile. The phase step, in combination with the attenuation of the
periodic subpulse modulation at pulse longitudes near the step, suggests that
the patterns arise from the addition of two superposed components of nearly
opposite drift phase and differing longitudinal dependence. We argue that since
there cannot be physical overlap of spark patterns on the polar cap, the drift
components must be associated with a kind of ``multiple imaging'' of a single
polar cap ``carousel'' spark pattern. One possibility is that the two
components correspond to refracted rays originating from opposite sides of the
polar cap. A second option associates the components with emission from two
altitudes in the magnetosphere.Comment: 10 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
STEPWISE - STructured lifestyle Education for People WIth SchizophrEnia : a study protocol for a randomised controlled trial
BACKGROUND: People with schizophrenia are two to three times more likely to be overweight than the general population. The UK National Institute of Health and Care Excellence (NICE) recommends an annual physical health review with signposting to, or provision of, a lifestyle programme to address weight concerns and obesity. The purpose of this randomised controlled trial is to assess whether a group-based structured education programme can help people with schizophrenia to lose weight. METHODS: Design: a randomised controlled trial of a group-based structured education programme. SETTING: 10 UK community mental health trusts. PARTICIPANTS: 396 adults with schizophrenia, schizoaffective, or first-episode psychosis who are prescribed antipsychotic medication will be recruited. Participants will be overweight, obese or be concerned about their weight. INTERVENTION: participants will be randomised to either the intervention or treatment as usual (TAU). The intervention arm will receive TAU plus four 2.5-h weekly sessions of theory-based lifestyle structured group education, with maintenance contact every 2 weeks and 'booster' sessions every 3 months. All participants will receive standardised written information about healthy eating, physical activity, alcohol and smoking. OUTCOMES: the primary outcome is weight (kg) change at 1 year post randomisation. Secondary outcomes, which will be assessed at 3 and 12 months, include: the proportion of participants who maintained or reduced their weight; waist circumference; body mass index; objectively measured physical activity (wrist accelerometer); self-reported diet; blood pressure; fasting plasma glucose, lipid profile and HbA1c (baseline and 1 year only); health-related quality of life (EQ-5D-5L and RAND SF-36); (adapted) brief illness perception questionnaire; the Brief Psychiatric Rating Scale; the Client Service Receipt Inventory; medication use; smoking status; adverse events; depression symptoms (Patient Health Questionnaire-9); use of weight-loss programmes; and session feedback (intervention only). Outcome assessors will be blind to trial group allocation. Qualitative interviews with a subsample of facilitators and invention-arm participants will provide data on intervention feasibility and acceptability. Assessment of intervention fidelity will also be performed. DISCUSSION: The STEPWISE trial will provide evidence for the clinical and cost-effectiveness of a tailored intervention, which, if successful, could be implemented rapidly in the NHS. TRIAL REGISTRATION: ISRCTN19447796 , registered on 20 March 2014
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