Number Formats, Error Mitigation, and Scope for 16-Bit Arithmetics in Weather and Climate Modeling Analyzed With a Shallow Water Model

The need for high-precision calculations with 64-bit or 32-bit floating-point arithmetic for weather and climate models is questioned. Lower-precision numbers can accelerate simulations and are increasingly supported by modern computing hardware. This paper investigates the potential of 16-bit arithmetic when applied within a shallow water model that serves as a medium complexity weather or climate application. There are several 16-bit number formats that can potentially be used (IEEE half precision, BFloat16, posits, integer, and fixed-point). It is evident that a simple change to 16-bit arithmetic will not be possible for complex weather and climate applications as it will degrade model results by intolerable rounding errors that cause a stalling of model dynamics or model instabilities. However, if the posit number format is used as an alternative to the standard floating-point numbers, the model degradation can be significantly reduced. Furthermore, mitigation methods, such as rescaling, reordering, and mixed precision, are available to make model simulations resilient against a precision reduction. If mitigation methods are applied, 16-bit floating-point arithmetic can be used successfully within the shallow water model. The results show the potential of 16-bit formats for at least parts of complex weather and climate models where rounding errors would be entirely masked by initial condition, model, or discretization error.

Discretization of the Bloch sphere, fractal invariant sets and Bell's theorem

An arbitrarily dense discretization of the Bloch sphere of complex Hilbert states is constructed, where points correspond to bit strings of fixed finite length. Number-theoretic properties of trigonometric functions (not part of the quantum-theoretic canon) are used to show that this constructive discretized representation incorporates many of the defining characteristics of quantum systems: completementarity, uncertainty relationships and (with a simple Cartesian product of discretized spheres) entanglement. Unlike Meyer's earlier discretization of the Bloch Sphere, there are no orthonormal triples, hence the Kocken-Specker theorem is not nullified. A physical interpretation of points on the discretized Bloch sphere is given in terms of ensembles of trajectories on a dynamically invariant fractal set in state space, where states of physical reality correspond to points on the invariant set. This deterministic construction provides a new way to understand the violation of the Bell inequality without violating statistical independence or factorization, where these conditions are defined solely from states on the invariant set. In this finite representation, there is an upper limit to the number of qubits that can be entangled, a property with potential experimental consequences.

The physics of numerical analysis: a climate modelling case study

The case is made for a much closer synergy between climate science, numerical analysis and computer science. This article is part of a discussion meeting issue 'Numerical algorithms for high-performance computational science'.

The Impact of a Stochastic Parameterization Scheme on Climate Sensitivity in EC-Earth

Stochastic schemes, designed to represent unresolved subgrid-scale variability, are frequently used in short and medium-range weather forecasts, where they are found to improve several aspects of the model. In recent years, the impact of stochastic physics has also been found to be beneficial for the model's long-term climate. In this paper, we demonstrate for the first time that the inclusion of a stochastic physics scheme can notably affect a model's projection of global warming, as well as its historical climatological global temperature. Specifically, we find that when including the "stochastically perturbed parametrization tendencies" (SPPT) scheme in the fully coupled climate model EC-Earth v3.1, the predicted level of global warming between 1850 and 2100 is reduced by 10% under an RCP8.5 forcing scenario. We link this reduction in climate sensitivity to a change in the cloud feedbacks with SPPT. In particular, the scheme appears to reduce the positive low cloud cover feedback and increase the negative cloud optical feedback. A key role is played by a robust, rapid increase in cloud liquid water with SPPT, which we speculate is due to the scheme's nonlinear interaction with condensation.

Experimental Non-Violation of the Bell Inequality

A finite non-classical framework for qubit physics is described that challenges the conclusion that the Bell Inequality has been shown to have been violated experimentally, even approximately. This framework postulates the primacy of a fractal-like ‘invariant set’ geometry IU in cosmological state space, on which the universe evolves deterministically and causally, and from which space-time and the laws of physics in space-time are emergent. Consistent with the assumed primacy of IU, a non-Euclidean (and hence non-classical) metric gp is defined in cosmological state space. Here, p is a large but finite integer (whose inverse may reflect the weakness of gravity). Points that do not lie on IU are necessarily gp-distant from points that do. gp is related to the p-adic metric of number theory. Using number-theoretic properties of spherical triangles, the Clauser-Horne-Shimony-Holt (CHSH) inequality, whose violation would rule out local realism, is shown to be undefined in this framework. Moreover, the CHSH-like inequalities violated experimentally are shown to be gp-distant from the CHSH inequality. This result fails in the singular limit p=∞, at which gp is Euclidean and the corresponding model classical. Although Invariant Set Theory is deterministic and locally causal, it is not conspiratorial and does not compromise experimenter free will. The relationship between Invariant Set Theory, Bohmian Theory, The Cellular Automaton Interpretation of Quantum Theory and p-adic Quantum Theory is discussed.

A personal perspective on modelling the climate system

Given their increasing relevance for society, I suggest that the climate science community itself does not treat the development of error-free ab initio models of the climate system with sufficient urgency. With increasing levels of difficulty, I discuss a number of proposals for speeding up such development. Firstly, I believe that climate science should make better use of the pool of post-PhD talent in mathematics and physics, for developing next-generation climate models. Secondly, I believe there is more scope for the development of modelling systems which link weather and climate prediction more seamlessly. Finally, here in Europe, I call for a new European Programme on Extreme Computing and Climate to advance our ability to simulate climate extremes, and understand the drivers of such extremes. A key goal for such a programme is the development of a 1 km global climate system model to run on the first exascale supercomputers in the early 2020s.

On the use of programmable hardware and reduced numerical precision in earth-system modeling

Programmable hardware, in particular Field Programmable Gate Arrays (FPGAs), promises a significant increase in computational performance for simulations in geophysical fluid dynamics compared with CPUs of similar power consumption. FPGAs allow adjusting the representation of floating-point numbers to specific application needs. We analyze the performance-precision trade-off on FPGA hardware for the two-scale Lorenz '95 model. We scale the size of this toy model to that of a high-performance computing application in order to make meaningful performance tests. We identify the minimal level of precision at which changes in model results are not significant compared with a maximal precision version of the model and find that this level is very similar for cases where the model is integrated for very short or long intervals. It is therefore a useful approach to investigate model errors due to rounding errors for very short simulations (e.g., 50 time steps) to obtain a range for the level of precision that can be used in expensive long-term simulations. We also show that an approach to reduce precision with increasing forecast time, when model errors are already accumulated, is very promising. We show that a speed-up of 1.9 times is possible in comparison to FPGA simulations in single precision if precision is reduced with no strong change in model error. The single-precision FPGA setup shows a speed-up of 2.8 times in comparison to our model implementation on two 6-core CPUs for large model setups.

Bell's conspiracy, Schrödinger's black cat and global invariant sets

A locally causal hidden-variable theory of quantum physics need not be constrained by the Bell inequalities if this theory also partially violates the measurement independence condition. However, such violation can appear unphysical, implying implausible conspiratorial correlations between the hidden variables of particles being measured and earlier determinants of instrumental settings. A novel physically plausible explanation for such correlations is proposed, based on the hypothesis that states of physical reality lie precisely on a non-computational measure-zero dynamically invariant set in the state space of the universe: the Cosmological Invariant Set Postulate. To illustrate the relevance of the concept of a global invariant set, a simple analogy is considered where a massive object is propelled into a black hole depending on the decay of a radioactive atom. It is claimed that a locally causal hidden-variable theory constrained by the Cosmological Invariant Set Postulate can violate the Clauser-Horne-Shimony-Holt inequality without being conspiratorial, superdeterministic, fine-tuned or retrocausal, and the theory readily accommodates the classical compatibilist notion of (experimenter) free will.

Impact of hindcast length on estimates of seasonal climate predictability

It has recently been argued that single-model seasonal forecast ensembles are overdispersive, implying that the real world is more predictable than indicated by estimates of so-called perfect model predictability, particularly over the North Atlantic. However, such estimates are based on relatively short forecast data sets comprising just 20 years of seasonal predictions. Here we study longer 40 year seasonal forecast data sets from multimodel seasonal forecast ensemble projects and show that sampling uncertainty due to the length of the hindcast periods is large. The skill of forecasting the North Atlantic Oscillation during winter varies within the 40 year data sets with high levels of skill found for some subperiods. It is demonstrated that while 20 year estimates of seasonal reliability can show evidence of overdispersive behavior, the 40 year estimates are more stable and show no evidence of overdispersion. Instead, the predominant feature on these longer time scales is underdispersion, particularly in the tropics.

KEY POINTS

Predictions can appear overdispersive due to hindcast length sampling errorLonger hindcasts are more robust and underdispersive, especially in the tropicsTwenty hindcasts are an inadequate sample size to assess seasonal forecast skill.

On the reliability of seasonal climate forecasts

Seasonal climate forecasts are being used increasingly across a range of application sectors. A recent UK governmental report asked: how good are seasonal forecasts on a scale of 1-5 (where 5 is very good), and how good can we expect them to be in 30 years time? Seasonal forecasts are made from ensembles of integrations of numerical models of climate. We argue that 'goodness' should be assessed first and foremost in terms of the probabilistic reliability of these ensemble-based forecasts; reliable inputs are essential for any forecast-based decision-making. We propose that a '5' should be reserved for systems that are not only reliable overall, but where, in particular, small ensemble spread is a reliable indicator of low ensemble forecast error. We study the reliability of regional temperature and precipitation forecasts of the current operational seasonal forecast system of the European Centre for Medium-Range Weather Forecasts, universally regarded as one of the world-leading operational institutes producing seasonal climate forecasts. A wide range of 'goodness' rankings, depending on region and variable (with summer forecasts of rainfall over Northern Europe performing exceptionally poorly) is found. Finally, we discuss the prospects of reaching '5' across all regions and variables in 30 years time.

On the use of inexact, pruned hardware in atmospheric modelling

Inexact hardware design, which advocates trading the accuracy of computations in exchange for significant savings in area, power and/or performance of computing hardware, has received increasing prominence in several error-tolerant application domains, particularly those involving perceptual or statistical end-users. In this paper, we evaluate inexact hardware for its applicability in weather and climate modelling. We expand previous studies on inexact techniques, in particular probabilistic pruning, to floating point arithmetic units and derive several simulated set-ups of pruned hardware with reasonable levels of error for applications in atmospheric modelling. The set-up is tested on the Lorenz '96 model, a toy model for atmospheric dynamics, using software emulation for the proposed hardware. The results show that large parts of the computation tolerate the use of pruned hardware blocks without major changes in the quality of short- and long-time diagnostics, such as forecast errors and probability density functions. This could open the door to significant savings in computational cost and to higher resolution simulations with weather and climate models.

More reliable forecasts with less precise computations: a fast-track route to cloud-resolved weather and climate simulators?

This paper sets out a new methodological approach to solving the equations for simulating and predicting weather and climate. In this approach, the conventionally hard boundary between the dynamical core and the sub-grid parametrizations is blurred. This approach is motivated by the relatively shallow power-law spectrum for atmospheric energy on scales of hundreds of kilometres and less. It is first argued that, because of this, the closure schemes for weather and climate simulators should be based on stochastic-dynamic systems rather than deterministic formulae. Second, as high-wavenumber elements of the dynamical core will necessarily inherit this stochasticity during time integration, it is argued that the dynamical core will be significantly over-engineered if all computations, regardless of scale, are performed completely deterministically and if all variables are represented with maximum numerical precision (in practice using double-precision floating-point numbers). As the era of exascale computing is approached, an energy- and computationally efficient approach to cloud-resolved weather and climate simulation is described where determinism and numerical precision are focused on the largest scales only.

Stochastic parametrizations and model uncertainty in the Lorenz '96 system

Simple chaotic systems are useful tools for testing methods for use in numerical weather simulations owing to their transparency and computational cheapness. The Lorenz system was used here; the full system was defined as 'truth', whereas a truncated version was used as a testbed for parametrization schemes. Several stochastic parametrization schemes were investigated, including additive and multiplicative noise. The forecasts were started from perfect initial conditions, eliminating initial condition uncertainty. The stochastically generated ensembles were compared with perturbed parameter ensembles and deterministic schemes. The stochastic parametrizations showed an improvement in weather and climate forecasting skill over deterministic parametrizations. Including a temporal autocorrelation resulted in a significant improvement over white noise, challenging the standard idea that a parametrization should only represent sub-gridscale variability. The skill of the ensemble at representing model uncertainty was tested; the stochastic ensembles gave better estimates of model uncertainty than the perturbed parameter ensembles. The forecasting skill of the parametrizations was found to be linked to their ability to reproduce the climatology of the full model. This is important in a seamless prediction system, allowing the reliability of short-term forecasts to provide a quantitative constraint on the accuracy of climate predictions from the same system.

The Invariant Set Postulate: a new geometric framework for the foundations of quantum theory and the role played by gravity

A new law of physics is proposed, defined on the cosmological scale but with significant implications for the microscale. Motivated by nonlinear dynamical systems theory and black-hole thermodynamics, the Invariant Set Postulate proposes that cosmological states of physical reality belong to a non-computable fractal state-space geometry I , invariant under the action of some subordinate deterministic causal dynamics D I . An exploratory analysis is made of a possible causal realistic framework for quantum physics based on key properties of I . For example, sparseness is used to relate generic counterfactual states to points p ∉ I of unreality, thus providing a geometric basis for the essential contextuality of quantum physics and the role of the abstract Hilbert Space in quantum theory. Also, self-similarity, described in a symbolic setting, provides a possible realistic perspective on the essential role of complex numbers and quaternions in quantum theory. A new interpretation is given to the standard ‘mysteries’ of quantum theory: superposition, measurement, non-locality, emergence of classicality and so on. It is proposed that heterogeneities in the fractal geometry of I are manifestations of the phenomenon of gravity. Since quantum theory is inherently blind to the existence of such state-space geometries, the analysis here suggests that attempts to formulate unified theories of physics within a conventional quantum-theoretic framework are misguided, and that a successful quantum theory of gravity should unify the causal non-Euclidean geometry of space–time with the atemporal fractal geometry of state space.

Impact of a quasi-stochastic cellular automaton backscatter scheme on the systematic error and seasonal prediction skill of a global climate model

The impact of a nonlinear dynamic cellular automaton (CA) model, as a representation of the partially stochastic aspects of unresolved scales in global climate models, is studied in the European Centre for Medium Range Weather Forecasts coupled ocean-atmosphere model. Two separate aspects are discussed: impact on the systematic error of the model, and impact on the skill of seasonal forecasts. Significant reductions of systematic error are found both in the tropics and in the extratropics. Such reductions can be understood in terms of the inherently nonlinear nature of climate, in particular how energy injected by the CA at the near-grid scale can backscatter nonlinearly to larger scales. In addition, significant improvements in the probabilistic skill of seasonal forecasts are found in terms of a number of different variables such as temperature, precipitation and sea-level pressure. Such increases in skill can be understood both in terms of the reduction of systematic error as mentioned above, and in terms of the impact on ensemble spread of the CA's representation of inherent model uncertainty.

Introduction. Stochastic physics and climate modelling

Finite computing resources limit the spatial resolution of state-of-the-art global climate simulations to hundreds of kilometres. In neither the atmosphere nor the ocean are small-scale processes such as convection, clouds and ocean eddies properly represented. Climate simulations are known to depend, sometimes quite strongly, on the resulting bulk-formula representation of unresolved processes. Stochastic physics schemes within weather and climate models have the potential to represent the dynamical effects of unresolved scales in ways which conventional bulk-formula representations are incapable of so doing. The application of stochastic physics to climate modelling is a rapidly advancing, important and innovative topic. The latest research findings are gathered together in the Theme Issue for which this paper serves as the introduction.

Fiber-specific responses of muscle glycogen repletion in fasted rats physically active during recovery from high-intensity physical exertion

Mild physical activity performed immediately after a bout of intense exercise in fasting humans results in net glycogen breakdown in their slow oxidative (SO) muscle fibers and glycogen repletion in their fast twitch (FT) fibers. Because several animal species carry a low proportion of SO fibers, it is unclear whether they can also replenish glycogen in their FT fibers under these conditions. Given that most skeletal muscles in rats are poor in SO fibers (<5%), this issue was examined using groups of 24-h fasted Wistar rats (n=10) that swam for 3 min at high intensity with a 10% weight followed by either a 60-min rest (passive recovery, PR) or a 30-min swim with a 0.5% weight (active recovery, AR) preceding a 30-min rest. The 3-min sprint caused 61-79% glycogen fall across the muscles examined, but not in the soleus (SOL). Glycogen repletion during AR without food was similar to PR in the white gastrocnemius (WG), where glycogen increased by 71%, and less than PR in both the red and mixed gastrocnemius (RG, MG). Glycogen fell by 26% during AR in the SOL. Following AR, glycogen increased by 36%, 87%, and 37% in the SOL, RG, and MG, respectively, and this was accompanied by the sustained activation of glycogen synthase and inhibition of glycogen phosphorylase in the RG and MG. These results suggest that mammals with a low proportion of SO fibers can also replenish the glycogen stores of their FT fibers under extreme conditions combining physical activity and fasting.

Ensemble decadal predictions from analysed initial conditions

Sensitivity experiments using a coupled model initialized from analysed atmospheric and oceanic observations are used to investigate the potential for interannual-to-decadal predictability. The potential for extending seasonal predictions to longer time scales is explored using the same coupled model configuration and initialization procedure as used for seasonal prediction. It is found that, despite model drift, climatic signals on interannual-to-decadal time scales appear to be detectable. Two climatic states have been chosen: one starting in 1965, i.e. ahead of a period of global cooling, and the other in 1994, ahead of a period of global warming. The impact of initial conditions and of the different levels of greenhouse gases are isolated in order to gain insights into the source of predictability.

Probabilistic prediction of climate using multi-model ensembles: from basics to applications

The development of multi-model ensembles for reliable predictions of inter-annual climate fluctuations and climate change, and their application to health, agronomy and water management, are discussed.

Malaria early warnings based on seasonal climate forecasts from multi-model ensembles

The control of epidemic malaria is a priority for the international health community and specific targets for the early detection and effective control of epidemics have been agreed. Interannual climate variability is an important determinant of epidemics in parts of Africa where climate drives both mosquito vector dynamics and parasite development rates. Hence, skilful seasonal climate forecasts may provide early warning of changes of risk in epidemic-prone regions. Here we discuss the development of a system to forecast probabilities of anomalously high and low malaria incidence with dynamically based, seasonal-timescale, multi-model ensemble predictions of climate, using leading global coupled ocean-atmosphere climate models developed in Europe. This forecast system is successfully applied to the prediction of malaria risk in Botswana, where links between malaria and climate variability are well established, adding up to four months lead time over malaria warnings issued with observed precipitation and having a comparably high level of probabilistic prediction skill. In years in which the forecast probability distribution is different from that of climatology, malaria decision-makers can use this information for improved resource allocation.

Metabolic effects of alcohol on skeletal muscle

The purpose of this review is to summarize our current understanding of the acute and chronic interactions between alcohol and nutrient metabolism in skeletal muscle. Insulin is well known to play an important regulatory role in nutrient, especially glucose, uptake and utilization in skeletal muscle. Several studies have shown that alcohol can acutely reduce the normal metabolic responses of skeletal muscle to the action of insulin. The most obvious of these is an acute impairment in glucose metabolism associated with alcohol consumption. While the exact mechanism(s) underlying this acute insulin resistance is presently unclear, several possible factors are discussed in this review. In contrast to these short-term effects, the effects of alcohol on skeletal muscle insulin sensitivity in chronic alcohol abusers are not as well established. Chronic alcohol abuse is known to be associated with skeletal myopathies, believed to result from alcohol induced abnormalities in muscle protein synthesis. Finally, the alcohol-mediated impairments of many aspects of skeletal muscle metabolism are discussed in relation to the insulin resistance associated broad spectrum of common lifestyle-related disorders, including non-insulin dependent diabetes mellitus and obesity, the consequences of which may be important to the pathogenesis of alcohol-related diseases.

Alcohol and glucose metabolism in skeletal muscles in the rat

Ethanol is known to cause an acute and profound insulin resistance in man and the rat primarily via effects on glucose utilization. This paper examines the nature of these inhibitory effects on whole-body glucose utilization using the euglycaemic hyperinsulinaemic clamp in the conscious unrestrained rat. We confirm that ethanol infusion causes an acute insulin resistance, the rate of glucose infusion required to maintain euglycaemia (GIR) being decreased markedly by ethanol. To ensure that the GIR is a measure of whole-body glucose disposal, glucose turnover and hepatic glycogen levels were measured. These studies showed that ethanol totally suppressed hepatic glucose production. The reduction in GIR is associated with marked decreases in glucose uptake and glycogen synthesis in most skeletal muscles. In oxidative but not in non-oxidative muscles, the activation of glycogen synthase in response to insulin was decreased by ethanol, suggesting that a defect in glycogen synthase activation may be responsible for the decrease in glycogen synthesis. The basis of the inhibitory effects of ethanol on insulin-stimulated glucose metabolism in muscle is unknown, but may involve membrane-associated impairments in insulin signalling and/or the glucose transport system.

Acute ethanol-mediated insulin resistance in the rat: the role of ethanol oxidation

Ethanol causes an acute and profound insulin resistance in humans and in the rat. Recent studies indicate that defects in skeletal muscle glucose uptake and utilization make a major contribution to this insulin resistance. In this study, we used the euglycaemic hyperinsulinaemic clamp to examine the role that hepatic ethanol oxidation via alcohol dehydrogenase (ADH) plays in the acute insulin resistance caused by ethanol in the rat. Treatment with the ADH inhibitor 4-methylpyrazole (4-MP) failed to abolish the insulin resistance as expressed as a decrease in the rate of glucose infusion required to maintain euglycaemia (GIR). A decrease in GIR was also observed in response to tert-butanol, an alcohol that is not a substrate for hepatic ADH. These results indicate that oxidation via ADH is not a prerequisite for the inhibition by ethanol of whole-body glucose utilization. In a separate study, we examined the relationship between blood ethanol concentration and GIR in order to determine the potency of ethanol in causing insulin resistance. These experiments showed that even at low blood concentrations (<2 mM), ethanol caused a profound decrease in GIR, similar in magnitude to that observed at higher blood concentrations (approximately 40 mM)

Ethanol acutely impairs glycogen repletion in skeletal muscle following high intensity short duration exercise in the rat

Ethanol is recognized to affect adversely carbohydrate metabolism in skeletal muscle. This paper seeks to establish whether ethanol acutely impairs glycogen repletion during recovery from high intensity short duration exercise in the rat. High intensity exercise caused the massive mobilization of glycogen stores in muscles rich in type IIa and IIb fibres and marked increases in plasma and muscle lactate levels. During the 30-minute recovery period, there was substantial glycogen repletion in these muscles in both the ethanol-treated and control rats. Ethanol, however, was associated with reduced glycogen resynthesis in both the tibialis anterior (by 22%) and red gastrocnemius (by 31%) muscles but not in the white gastrocnemius muscle. This reduction in post-exercise glycogen deposition was accompanied by decreased lactate disposal and elevated plasma glucose levels. These effects of ethanol on glycogen repletion may involve interactions with hepatic gluconeogenesis, glucose uptake and utilization in muscle, muscle glycogen synthesis and lactate glyconeogenesis. The ethanol-mediated impairment in post-exercise glycogen repletion may have important implications for the pathogenesis of chronic alcoholic skeletal myopathy.

Glycogen resynthesis in the absence of food ingestion during recovery from moderate or high intensity physical activity: novel insights from rat and human studies

The finding that during recovery from high intensity exercise, rats have the capacity to replenish their muscle glycogen stores even in the absence of food intake has provided us with an experimental model of choice to explore further this process. Our objective here is to share those questions arising from research carried out by others and ourselves on rats and humans that are likely to be of interest to comparative biochemists/physiologists. On the basis of our findings and those of others, it is proposed that across vertebrate species: (1). the capacity of muscles to replenish their glycogen stores from endogenous carbon sources is dependent on the type of physical activity and animal species; (2). lactate and amino acids are the major endogenous carbon sources mobilized for the resynthesis of muscle glycogen during recovery from exercise, their relative contributions depending on the duration of recovery and type of exercise; (3). the relative contributions of lactate glyconeogenesis and hepatic/renal gluconeogenesis to muscle glycogen synthesis is species- and muscle fiber-dependent; and (4). glycogen synthase and phosphorylase play an important role in the control of the rate of glycogen synthesis post-exercise, with the role of glucose transport being species-dependent.

Quantifying the risk of extreme seasonal precipitation events in a changing climate

Increasing concentrations of atmospheric carbon dioxide will almost certainly lead to changes in global mean climate. But because--by definition--extreme events are rare, it is significantly more difficult to quantify the risk of extremes. Ensemble-based probabilistic predictions, as used in short- and medium-term forecasts of weather and climate, are more useful than deterministic forecasts using a 'best guess' scenario to address this sort of problem. Here we present a probabilistic analysis of 19 global climate model simulations with a generic binary decision model. We estimate that the probability of total boreal winter precipitation exceeding two standard deviations above normal will increase by a factor of five over parts of the UK over the next 100 years. We find similar increases in probability for the Asian monsoon region in boreal summer, with implications for flooding in Bangladesh. Further practical applications of our techniques would be helped by the use of larger ensembles (for a more complete sampling of model uncertainty) and a wider range of scenarios at a resolution adequate to analyse average-size river basins.

Effect of acute and chronic alcohol treatment and their superimposition on lysosomal, cytoplasmic, and proteosomal protease activities in rat skeletal muscle in vivo

Alcohol can be considered as a nutritional toxin when ingested in excess amounts and leads to skeletal muscle myopathy. We hypothesized that altered protease activities contribute to this phenomenon, and that differential effects on protease activities may occur when: (1) rats at different stages in their development are administered alcohol in vivo; (2) acute ethanol treatment is superimposed on chronic alcohol-feeding in vivo; and (3) muscles are exposed to alcohol and acetaldehyde in vivo and in vitro. In acute studies, rats weighing approximately 0.1 kg (designated immature) or approximately 0.25 kg (designated mature) body weight (BW) were dosed acutely with alcohol (75 mmol/kg BW; intraperitoneal [IP], 2.5 hours prior to killing) or identically treated with 0.15 mol/L NaCl as controls. In chronic studies, rats (approximately 0.1 kg BW) were fed between 1 to 6 weeks, with 35% of dietary energy as ethanol, controls were identically treated with isocaloric glucose. Other studies included administration of cyanamide (aldehyde dehydrogenase inhibitor) in vivo or addition of alcohol and acetaldehyde to muscle preparations in vitro. At the end of the treatments, cytoplasmic (alanyl-, arginyl-, leucyl-, prolyl-, tripeptidyl-aminopeptidase and dipeptidyl aminopeptidase IV), lysosomal (cathepsins B, D, H, and L, dipeptidyl aminopeptidase I and II), proteasomal (chymotrypsin-, trypsin-like, and peptidylglutamyl peptide hydrolase activities) and Ca(2+)-activated (micro- and milli-calpain and calpastatin) activities were assayed. (1) Acute alcohol dosage in mature rats reduced the activities of alanyl-, arginyl- and leucyl aminopeptidase (cytoplasmic), dipeptidyl aminopeptidase II (lysosomal), and the chymotrypsin- and trypsin-like activities (proteosomal). No significant effects were observed in similarly treated immature rats. (2) Alcohol feeding in immature rats did not alter the activities of any of the enzymes assayed at 6 weeks. (3) In immature rats, activities of cathepsins B and D were not overtly affected at either 3, 7, 14, 28, or 42 days. (4) Superimposing acute (2.5 hours) on chronic (4 weeks feeding of immature rats) ethanol treatment (ie, chronic + acute) reduced the activities of cytoplasmic proline aminopeptidase and the chymotrypsin- and trypsin-like activities of the proteasome. (5) Cathepsin D activities were reduced in muscle homogenates upon addition of alcohol and acetaldehyde in vitro. (6) Cyanamide pretreatment in combination with alcohol dosage in immature rats did not significantly alter any protease activities. The data suggests that mature rats are more sensitive to the effects of acute alcohol on muscle proteases. Protease activities may be affected by acetaldehyde or alcohol levels as indicated by in vitro experiments. The reduction in muscle protease activities in chronic + acute alcohol superimposition may reflect the effect of acute alcohol dosage alone. Overall, there was no evidence for increased protease activity in any of the experimental situations.

Muscle glycogen supercompensation: absence of a gender-related difference

Recently it has been reported that women do not have the capacity to accumulate supranormal levels of muscle glycogen when subjected to a carbohydrate (CHO) loading regimen [Tarnopolsky et al. (1995) J Appl Physiol 78:1360-1368]. Since, in this study, CHO intake relative to body mass in the female subjects was much lower than that in males, our primary aim was to re-examine this issue using subjects fed comparable amounts of CHO. Endurance-trained female and male subjects ingested 12 g CHO x kg(-1) lean body mass day(-1) in conjunction with the cessation of their daily physical training. A 3-day exposure to this diet resulted in a marked rise in muscle glycogen levels from [mean (SD)] 108 (15) mmol x kg(-1) wet weight to 193 (14) mmol x kg(-1) wet weight and 111 (16) m mol x kg(-1) wet weight to 202 (20) mmol x kg(-1) wet weight in the female participants during the post-menstrual and pre-menstrual phases of their menstrual cycle, respectively, and from 109 (27) mmol x kg(-1) wet weight to 183 (25) mmol x kg(-1) wet weight in males. We conclude that (1) female athletes have the capacity to accumulate supranormal levels of muscle glycogen, and (2) when exercise-trained males and females are fed comparable amounts of CHO relative to lean body mass, there is no gender-related difference in their ability to accumulate supranormal levels of muscle glycogen.

Alcoholic myopathy: biochemical mechanisms

Between one- and two-thirds of all alcohol abusers have impairment of muscle function that may be accompanied by biochemical lesions and/or the presence of a defined myopathy characterised by selective atrophy of Type II fibres. Perturbations in protein metabolism are central to the effects on muscle and account for the reductions in muscle mass and fibre diameter. Ethanol abuse is also associated with abnormalities in carbohydrate (as well as lipid) metabolism in skeletal muscle. Ethanol-mediated insulin resistance is allied with the inhibitory effects of ethanol on insulin-stimulated carbohydrate metabolism. It acutely impairs insulin-stimulated glucose and lipid metabolism, although it is not known whether it has an analogous effect on insulin-stimulated protein synthesis. In alcoholic cirrhosis, insulin resistance occurs with respect to carbohydrate metabolism, although the actions of insulin to suppress protein degradation and stimulate amino acid uptake are unimpaired. In acute alcohol-dosing studies defective rates of protein synthesis occur, particularly in Type II fibre-predominant muscles. The relative amounts of mRNA-encoding contractile proteins do not appear to be adversely affected by chronic alcohol feeding, although subtle changes in muscle protein isoforms may occur. There are also rapid and sustained reductions in total (largely ribosomal) RNA in chronic studies. Loss of RNA appears to be related to increases in the activities of specific muscle RNases in these long-term studies. However, in acute dosing studies (less than 1 day), the reductions in muscle protein synthesis are not due to overt loss of total RNA. These data implicate a role for translational modifications in the initial stages of the myopathy, although changes in transcription and/or protein degradation may also be superimposed. These events have important implications for whole-body metabolism.

Effect of streptozotocin-induced diabetes on glycogen resynthesis in fasted rats post-high-intensity exercise

It has recently been shown that food intake is not essential for the resynthesis of the stores of muscle glycogen in fasted animals recovering from high-intensity exercise. Because the effect of diabetes on this process has never been examined before, we undertook to explore this issue. To this end, groups of rats were treated with streptozotocin (60 mg/kg body mass ip) to induce mild diabetes. After 11 days, each animal was fasted for 24 h before swimming with a lead weight equivalent to 9% body mass attached to the tail. After exercise, the rate and the extent of glycogen repletion in muscles were not affected by diabetes, irrespective of muscle fiber composition. Consistent with these findings, the effect of exercise on the phosphorylation state of glycogen synthase in muscles was only minimally affected by diabetes. In contrast to its effects on nondiabetic animals, exercise in fasted diabetic rats was accompanied by a marked fall in hepatic glycogen levels, which, surprisingly, increased to preexercise levels during recovery despite the absence of food intake.

Dominant action of mutated erythropoietin receptors on differentiation in vitro and erythroleukemia development in vivo

J2E cells produce rapid, fatal erythroleukemias in vivo but still respond to erythropoietin (epo) in vitro by differentiating, proliferating and remaining viable in the absence of serum. Mutant epo receptors were introduced into these cells to determine whether they could influence the different biological responses to epo in vitro and the development of erythroleukemias. Three mutant receptors were used as cytoplasmic truncation mutants Delta257 and Delta321 (above box 1 and below box 2 respectively), and the cytoplasmic point mutant W282R (defective for JAK2 activation). Strikingly, the Delta321 mutation produced a hyper-sensitive response in vitro to epo-induced differentiation and viability, but not to proliferation. In contrast with the Delta321 receptor, the Delta257 and W282R mutants inhibited all biological responses to epo due to impaired JAK2 phosphorylation. Significantly, erythroleukemias took almost twice as long to develop with cells containing the W282R mutation, indicating that JAK2 plays an important role in the emergence of these leukemias. These data demonstrate that mutant epo receptors dominantly altered responses of J2E cells to epo in culture and the development of erythroleukemias. Oncogene (2000) 19, 953 - 960.

Osmotic effects of ethanol on lymphocytes

The alterations in the immune system caused by ethanol appear to be a complex combination of direct and indirect effects. The role of ethanol as an osmolyte has previously been studied in this laboratory with rat splenocytes. In the present study the osmotic effects of ethanol were investigated in lymphocytes from human normal subjects and alcohol abusers. Mitogen-stimulated lymphocytes were cultured in vitro with ethanol in hyperosmotic isotonic or iso-osmotic hypotonic conditions. The former conditions mimic the physiological situation where ethanol increases osmolality in an electrolyte-balanced environment. Under these conditions, lymphocyte proliferation was unaffected. Ethanol addition in iso-osmotic hypotonic conditions, where there is electrolyte imbalance, was associated with inhibition of T-lymphocyte proliferation. Hyperosmotic hypertonic solutions in the absence of ethanol also resulted in inhibition of T-lymphocyte proliferation. Electron microscopy and measurement of cell viability and metabolic activity (lactate and ATP levels) indicated that the decreased proliferation associated with NaCl-induced hyperosmotic hypertonic conditions was at least partially attributable to cell death together with, and possibly caused by, detrimental effects on mitochondria. Conversely, decreased T-lymphocyte proliferation in iso-osmotic hypotonic high ethanol solutions, appeared not to be due to changes in cell viability, nor alterations to energy metabolism. It is proposed that ion fluxes involved in the maintenance of cell volume, in particular K ⁺ movement, may be important in facilitating normal lymphocyte proliferation in the presence of ethanol in pathological conditions associated with electrolyte imbalance.

Characterization of mouse glycogenin-1 cDNA and promoter region

Glycogenin-1 is an autocatalytic, self-glucosylating protein which acts as the primer for glycogen synthesis in mammalian skeletal muscle. In this study, we have cloned the glycogenin-1 cDNA from mouse skeletal muscle. Mouse glycogenin-1 has a predicted molecular mass of 37¿ omitted¿399 Da, and the deduced amino acid sequence exhibited 87% homology with human glycogenin-1. Northern blot analysis specifically detected mouse glycogenin-1 transcript in skeletal muscle and heart, and to a lesser extent in kidney, lung and brain. 5'-RACE analysis revealed the major transcription start site to be localized 47 bp upstream of the initiation of translation codon. Sequence analysis of approximately 2 kb of the 5'-flanking region revealed potentially important regions of homology between the mouse and human glycogenin-1 promoters. Several conserved but putative elements, including a TATA box, Sp1 site, and a cyclic AMP responsive element, were observed proximal to the transcription start site. Significantly, Northern blot analysis revealed dibutyryl-cAMP treatment of cultured mouse C2C12 myotubes markedly reduced the levels of glycogenin-1 mRNA in a dose-dependent manner.

Glycogen repletion following burst activity: a carbohydrate-sparing mechanism in animals adapted to arid environments?

The Western chestnut mouse (Pseudomys nanus ferculinus) is one of several native rodent species adapted to the arid environments of Australia. Since these environments are often associated with a paucity in dietary carbohydrate, the problem arises as to the mechanism whereby these rodents replete their stores of muscle glycogen when recovering from high intensity physical activity. This is an important issue since the maintenance of adequate stores of muscle glycogen is crucial to support the energy demands associated with 'flight or fight' responses. Whilst it is known that food ingestion post-exercise is required for the total repletion of muscle glycogen in rats and humans, our findings indicate that the Western chestnut mouse has the impressive capacity to replete completely its stores of muscle glycogen, even in the absence of food intake. Indeed during recovery from burst activity which results in the massive breakdown of the stores of muscle glycogen, the levels of glycogen return back to pre-exercise levels within only 50 minutes despite the absence of food intake. This capacity is important in the broader context of nutritional adaptation to arid/seasonally-arid regions since it allows muscles to replete their fuel stores even when food is not available. How common is this strategy among desert-adapted mammal species is a question yet to be answered.

Characterization of the human glycogenin-1 gene: identification of a muscle-specific regulatory domain

The de-novo synthesis of glycogen is now known to involve a novel class of self-glucosylating protein primers. In mammalian skeletal muscle, glycogenin-1 is the protein responsible for this initiation step. Northern blot analysis revealed that glycogenin-1 gene transcription is differentially regulated in the C2C12 mouse muscle cell line. To define the regulatory elements that control expression of the glycogenin-1 gene, we have cloned and characterized the genomic structure of the human glycogenin-1 gene and its promoter region. This gene consists of seven exons and six introns, and spans over 13kb. Transcription of human glycogenin-1 is initiated at two major sites, 80 and 86bp upstream from the initiation of translation codon. Nucleotide sequence analysis of 2.1kb of the 5'-flanking region revealed the proximal promoter contains both a TATA box and two putative Sp1 binding sites located in a CpG island. There are numerous binding sites for developmental and cell-type-specific transcription factors, including AP-1, AP-2, GATA, and several potential Oct 1 binding domains. There are also nine consensus E-boxes that bind the basic helix-loop-helix family of muscle-specific transcription factors. The transcriptional activity of the glycogenin-1 gene was investigated by transient transfection of the 5'-flanking region in HepG2 cells and C2C12 myoblasts and myotubes. These results permitted the definition of a minimal 232bp promoter fragment that is responsible for basal level transcription in a cell-type-independent manner. Furthermore, we have identified a regulatory region located between -2076 and -1736 of the 5'-flanking region of the human glycogenin-1 gene that allows myotube-specific expression in C2C12 cells.

Alcohol-related diols cause acute insulin resistance in vivo

Epidemiological studies suggest that alcohol consumption is an independent risk factor for the development of non-insulin-dependent diabetes mellitus (NIDDM). Alcoholism is known to be associated with increased plasma levels of two novel diols, 2,3-butanediol and 1,2-propanediol, metabolites known to impair insulin action in isolated adipocytes. This study examines whether 2,3-butanediol and 1,2-propanediol have the capacity to impair insulin action acutely in vivo in the rat. Using the euglycemic-hyperinsulinemic clamp, it is shown that the two diols reduce whole-body glucose utilization (by approximately 30%), with the onset of insulin resistance in vivo occurring at plasma concentrations of 2,3-butanediol (33 micromol/L) at least one order of magnitude (P < .001) lower than 1,2-propanediol (432 micromol/L). Tracer methodologies using [U-14C]glucose and 2-deoxy[1-(3)H]glucose indicate that the reduction in whole-body glucose utilization is accompanied by a reduction in glucose uptake and glycogen synthesis in the skeletal muscle and heart. The association between elevated plasma diol levels and insulin resistance demonstrated in this report raises the question of whether there is a link between the high plasma diol levels in alcohol abusers and their increased susceptibility to NIDDM.

Prolonged exposure to halothane and associated changes in carbohydrate metabolism in rat muscles in vivo

Halothane, an anesthetic presently used in animal experimentation, is reported to stimulate glycogen breakdown in isolated preparations of rat skeletal muscles, suggesting that it may not be a suitable anesthetic for the study of glycogen metabolism in rats in vivo. The purpose of this study was to establish whether prolonged exposure to halothane in rats in vivo is associated with accelerated glycogenolysis. Exposure of rats to halothane for up to 1 h was not accompanied by either any change in the levels of glycogen or increase in activity ratios of glycogen phosphorylase in muscles, irrespective of their fiber compositions. In marked contrast, the levels of lactate, inorganic phosphate, glucose 1-phosphate, glucose 6-phosphate, fructose 1,6-bisphosphate, and fructose 2, 6-bisphosphate changed progressively during anesthesia. Accordingly, the interpretation of muscle metabolite levels must be performed with caution in experiments involving prolonged exposure to halothane. Overall, our findings indicate that the reported halothane-mediated stimulation of glycogen breakdown in vitro is likely to be an artifact and that halothane is a suitable anesthetic for experiments concerned with glycogen metabolism in rats.

Re-feeding after starvation involves a temporal shift in the control site of glycogen synthesis in rat muscle

The starved-to-fed transition is accompanied by rapid glycogen deposition in skeletal muscles. On the basis of recent findings [Bräu, Ferreira, Nikolovski, Raja, Palmer and Fournier (1997) Biochem. J. 322, 303-308] that during recovery from exercise there is a shift from a glucose 6-phosphate/phosphorylation-based control of glycogen synthesis to a phosphorylation-based control alone, this paper seeks to establish whether a similar shift occurs in muscle during re-feeding after starvation in the rat. Chow re-feeding after 48 h of starvation resulted in glycogen deposition in all muscles examined (white, red and mixed quadriceps, soleus and diaphragm) to levels higher than those in the fed state. Although the early phase of re-feeding was associated with increases in glucose 6-phosphate levels in all muscles, there was no accompanying increase in the fractional velocity of glycogen synthase except in the white quadriceps muscle. This finding, together with the observation that the fractional velocity of glycogen synthase in most muscles was already high in the starved state, suggests that in the initial phase of glycogen deposition the phosphorylation state of the enzyme may be adequate to support net glycogen synthesis. In the later phase of re-feeding, the progressive decrease in the fractional velocity of glycogen synthase in association with a decrease in the rate of glycogen deposition suggests that glycogen synthesis is controlled primarily by changes in the phosphorylation state of glycogen synthase. In conclusion, this study suggests that there is a temporal shift in the site of control of glycogen synthesis as glycogen deposition progresses during re-feeding after starvation.

Total contractile protein contents and gene expression in skeletal muscle in response to chronic ethanol consumption in the rat

An investigation was carried out to determine changes in the contents of skeletal muscle myofibrillary proteins (i.e., the contractile fraction composed principally of actin and myosin) and gene expression in skeletal muscle in response to ethanol feeding. Male Wistar rats were fed a nutritionally complete liquid diet, which contained 35% of total calories as ethanol. Controls were pair-fed isocaloric amounts of the same diet, in which ethanol was replaced by isocaloric glucose. Total mixed and contractile protein contents of the gastrocnemius in ethanol-fed rats were rapidly reduced by ethanol feeding: a response was discernible as early as 1 week after the commencement of the ethanol feeding regimen (approx. -10%, p < 0.025 and p = 0.05 for mixed and myofibrillary proteins, respectively). At 2, 4, and 6 weeks, mixed and myofibrillary protein contents were further reduced in alcohol-fed rats, by between 12% and 22%, compared to pair-fed controls. Similar changes occurred in the soluble (i.e., sarcoplasmic) protein fractions of skeletal muscle. At 2 weeks the composition of total messenger RNA and individual messenger RNA species was measured. Total messenger RNA content per muscle was reduced by 35% (p < 0.05). Messenger RNA levels for alpha-actin, beta-myosin heavy chain, and carbonic anhydrase III were not significantly altered. In conclusion, skeletal muscle protein contents are rapidly reduced by ethanol feeding, compared to pair-fed controls, though mRNA species encoding specific isoforms of myosin and actin are not affected. It is possible that chronic ethanol feeding may significantly alter the stability of mRNAs encoding other contractile proteins, or alternatively, defects in translation may predominate.

Regulation of glycogen synthase and phosphorylase during recovery from high-intensity exercise in the rat

The aim of this study was to determine the role of the phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulation of muscle glycogen repletion in fasted animals recovering from high-intensity exercise. Groups of rats were swum to exhaustion and allowed to recover for up to 120 min without access to food. Swimming to exhaustion caused substantial glycogen breakdown and lactate accumulation in the red, white and mixed gastrocnemius muscles, whereas the glycogen content in the soleus muscle remained stable. During the first 40 min of recovery, significant repletion of glycogen occurred in all muscles examined except the soleus muscle. At the onset of recovery, the activity ratios and fractional velocities of glycogen synthase in the red, white and mixed gastrocnemius muscles were higher than basal, but returned to pre-exercise levels within 20 min after exercise. In contrast, after exercise the activity ratios of glycogen phosphorylase in the same muscles were lower than basal, and increased to pre-exercise levels within 20 min. This pattern of changes in glycogen synthase and phosphorylase activities, never reported before, suggests that the integrated regulation of the phosphorylation state of both glycogen synthase and phosphorylase might be involved in the control of glycogen deposition after high-intensity exercise.

Muscle glycogen repletion from endogenous carbon sources during recovery from high intensity exercise in the fasted rat

During recovery from high intensity exercise, substantial and rapid muscle glycogen repletion from endogenous carbon sources is reported in a variety of vertebrate species, the rat being the only reported exception. The major aim of this study was to re-examine the process of glycogen repletion during recovery from high intensity exercise in the rat. In response to 3 min of vigorous swimming, muscle glycogen concentrations decrease markedly from initial levels of 20.2 +/- 1.5 and 21.2 +/- 0.9 mumol g-1 to 6.4 +/- 1.1 and 7.9 +/- 1.4 mumol g-1 in the tibialis anterior and plantaris muscles respectively. The equivalent of 58% of the glycogen carbons mobilized during exercise by the plantaris and 73% of that mobilized by the tibialis anterior muscle is repleted within 1 h following exercise. Using the hepatectomized rat as experimental model, a secondary aim of the study was to evaluate whether the liver is essential for the repletion of muscle glycogen. Although the absence of significant differences in the magnitude of post-exercise muscle glycogen repletion between sham-operated and hepatectomized rats suggests that the resynthesis of muscle glycogen can take place in the absence of hepatic gluconeogenesis, the present study identifies several limitations in the use of acute hepatectomy. Overall, the present study indicates that, in contrast to published views, the rat resembles other vertebrates in that it can support extensive muscle glycogen repletion from endogenous carbon sources during the recovery phase following high intensity exercise.