Showing papers by "University of Reading published in 2004"

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP

Abstract: A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

Regions of Strong Coupling Between Soil Moisture and Precipitation

Abstract: Previous estimates of land-atmosphere interaction (the impact of soil moisture on precipitation) have been limited by a lack of observational data and by the model dependence of computational estimates. To counter the second limitation, a dozen climate-modeling groups have recently performed the same highly controlled numerical experiment as part of a coordinated comparison project. This allows a multimodel estimation of the regions on Earth where precipitation is affected by soil moisture anomalies during Northern Hemisphere summer. Potential benefits of this estimation may include improved seasonal rainfall forecasts.

Dietary modulation of the human colonic microbiota: updating the concept of prebiotics

Abstract: Prebiotics are non-digestible (by the host) food ingredients that have a beneficial effect through their selective metabolism in the intestinal tract. Key to this is the specificity of microbial changes. The present paper reviews the concept in terms of three criteria: (a) resistance to gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption; (b) fermentation by intestinal microflora; (c) selective stimulation of the growth and/or activity of intestinal bacteria associated with health and wellbeing. The conclusion is that prebiotics that currently fulfil these three criteria are fructo-oligosaccharides, galacto-oligosaccharides and lactulose, although promise does exist with several other dietary carbohydrates. Given the range of food vehicles that may be fortified by prebiotics, their ability to confer positive microflora changes and the health aspects that may accrue, it is important that robust technologies to assay functionality are used. This would include a molecular-based approach to determine flora changes. The future use of prebiotics may allow species-level changes in the microbiota, an extrapolation into genera other than the bifidobacteria and lactobacilli, and allow preferential use in disease-prone areas of the body.

Role of oxygen radicals in DNA damage and cancer incidence

Abstract: The development of cancer in humans and animals is a multistep process. The complex series of cellular and molecular changes participating in cancer development are mediated by a diversity of endogenous and exogenous stimuli. One type of endogenous damage is that arising from intermediates of oxygen (dioxygen) reduction - oxygen-free radicals (OFR), which attacks not only the bases but also the deoxyribosyl backbone of DNA. Thanks to improvements in analytical techniques, a major achievement in the understanding of carcinogenesis in the past two decades has been the identification and quantification of various adducts of OFR with DNA. OFR are also known to attack other cellular components such as lipids, leaving behind reactive species that in turn can couple to DNA bases. Endogenous DNA lesions are genotoxic and induce mutations. The most extensively studied lesion is the formation of 8-OH-dG. This lesion is important because it is relatively easily formed and is mutagenic and therefore is a potential biomarker of carcinogenesis. Mutations that may arise from formation of 8-OH-dG involve GC --> TA transversions. In view of these findings, OFR are considered as an important class of carcinogens. The effect of OFR is balanced by the antioxidant action of non-enzymatic antioxidants as well as antioxidant enzymes. Non-enzymatic antioxidants involve vitamin C, vitamin E, carotenoids (CAR), selenium and others. However, under certain conditions, some antioxidants can also exhibit a pro-oxidant mechanism of action. For example, beta-carotene at high concentration and with increased partial pressure of dioxygen is known to behave as a pro-oxidant. Some concerns have also been raised over the potentially deleterious transition metal ion-mediated (iron, copper) pro-oxidant effect of vitamin C. Clinical studies mapping the effect of preventive antioxidants have shown surprisingly little or no effect on cancer incidence. The epidemiological trials together with in vitro experiments suggest that the optimal approach is to reduce endogenous and exogenous sources of oxidative stress, rather than increase intake of anti-oxidants. In this review, we highlight some major achievements in the study of DNA damage caused by OFR and the role in carcinogenesis played by oxidatively damaged DNA. The protective effect of antioxidants against free radicals is also discussed.

Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP

Abstract: New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue). ABSTRACT. New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).

Bayesian estimation of ancestral character states on phylogenies.

Abstract: Biologists frequently attempt to infer the character states at ancestral nodes of a phylogeny from the distribution of traits observed in contemporary organisms. Because phylogenies are normally inferences from data, it is desirable to account for the uncertainty in estimates of the tree and its branch lengths when making inferences about ancestral states or other comparative parameters. Here we present a general Bayesian approach for testing comparative hypotheses across statistically justified samples of phylogenies, focusing on the specific issue of reconstructing ancestral states. The method uses Markov chain Monte Carlo techniques for sampling phylogenetic trees and for investigating the parameters of a statistical model of trait evolution. We describe how to combine information about the uncertainty of the phylogeny with uncertainty in the estimate of the ancestral state. Our approach does not constrain the sample of trees only to those that contain the ancestral node or nodes of interest, and we show how to reconstruct ancestral states of uncertain nodes using a most-recent-common-ancestor approach. We illustrate the methods with data on ribonuclease evolution in the Artiodactyla. Software implementing the methods (BayesMultiState) is available from the authors.

Identifying adaptive genetic divergence among populations from genome scans

Abstract: The identification of signatures of natural selection in genomic surveys has become an area of intense research, stimulated by the increasing ease with which genetic markers can be typed. Loci identified as subject to selection may be functionally important, and hence (weak) candidates for involvement in disease causation. They can also be useful in determining the adaptive differentiation of populations, and exploring hypotheses about speciation. Adaptive differentiation has traditionally been identified from differences in allele frequencies among different populations, summarised by an estimate of FST. Low outliers relative to an appropriate neutral population-genetics model indicate loci subject to balancing selection, whereas high outliers suggest adaptive (directional) selection. However, the problem of identifying statistically significant departures from neutrality is complicated by confounding effects on the distribution of FST estimates, and current methods have not yet been tested in large-scale simulation experiments. Here, we simulate data from a structured population at many unlinked, diallelic loci that are predominantly neutral but with some loci subject to adaptive or balancing selection. We develop a hierarchical-Bayesian method, implemented via Markov chain Monte Carlo (MCMC), and assess its performance in distinguishing the loci simulated under selection from the neutral loci. We also compare this performance with that of a frequentist method, based on moment-based estimates of FST. We find that both methods can identify loci subject to adaptive selection when the selection coefficient is at least five times the migration rate. Neither method could reliably distinguish loci under balancing selection in our simulations, even when the selection coefficient is twenty times the migration rate.

A new method for diagnosing radiative forcing and climate sensitivity

Abstract: [1] We describe a new method for evaluating the radiative forcing, the climate feedback parameter (W m−2 K−1) and hence the effective climate sensitivity from any GCM experiment in which the climate is responding to a constant forcing. The method is simply to regress the top of atmosphere radiative flux against the global average surface air temperature change. This method does not require special integrations or off-line estimates, such as for stratospheric adjustment, to obtain the forcing, and eliminates the need for double radiation calculations and tropopause radiative fluxes. We show that for CO2 and solar forcing in a slab model and an AOGCM the method gives results consistent with those obtained by conventional methods. For a single integration it is less precise but since it does not require a steady state to be reached its precision could be improved by running an ensemble of short integrations.

Is Knowledge Power? Knowledge Flows, Subsidiary Power and Rent-Seeking within MNCs

Abstract: In recent years, as multinational corporation (MNC) subsidiaries have become more closely linked to international networks, their knowledge intensity has risen, and some of their R&D has gained a more creative role. Simultaneously, and often connectedly, many subsidiaries have acquired considerable strategic independence in all aspects of their operations, and therefore are able to exercise considerable intra-firm bargaining power to influence the distribution of the firm’s resources. In this context, we suggest that intra-MNC knowledge flows are a key determinant of subsidiary bargaining power. We argue that subsidiary managers can exploit such power to pursue their own ends. Such rent-seeking behavior is implicit in much of the literature on managerialism, but our analysis suggests that such behavior can now occur in headquarters–subsidiary and subsidiary–subsidiary relations. Thus subsidiary strategic independence, designed to enhance the competitiveness of outputs (market knowledge) and inputs (asset-seeking and learning), can be corroded when the pursuit of subsidiary objectives encourages rent-seeking. Empirical analysis of a sample of high-technology subsidiaries in the UK provides strong support for the theory. We examine several avenues whereby the incentives of units within the MNC can be aligned.

Amazonian forest dieback under climate-carbon cycle projections for the 21st century

Abstract: The first GCM climate change projections to include dynamic vegetation and an interactive carbon cycle produced a very significant amplification of global warming over the 21st century. Under the IS92a “business as usual” emissions scenario CO2 concentrations reached about 980 ppmv by 2100, which is about 280 ppmv higher than when these feedbacks were ignored. The major contribution to the increased CO2 arose from reductions in soil carbon because global warming is assumed to accelerate respiration. However, there was also a lesser contribution from an alarming loss of the Amazonian rainforest. This paper describes the phenomenon of Amazonian forest dieback under elevated CO2 in the Hadley Centre climate-carbon cycle model.

Concentrations of parabens in human breast tumours

Abstract: Parabens are used as preservatives in many thousands of cosmetic, food and pharmaceutical products to which the human population is exposed. Although recent reports of the oestrogenic properties of parabens have challenged current concepts of their toxicity in these consumer products, the question remains as to whether any of the parabens can accumulate intact in the body from the long-term, low-dose levels to which humans are exposed. Initial studies reported here show that parabens can be extracted from human breast tissue and detected by thin-layer chromatography. More detailed studies enabled identification and measurement of mean concentrations of individual parabens in samples of 20 human breast tumours by high-pressure liquid chromatography followed by tandem mass spectrometry. The mean concentration of parabens in these 20 human breast tumours was found to be 20.6 +/- 4.2 ng x g(-1) tissue. Comparison of individual parabens showed that methylparaben was present at the highest level (with a mean value of 12.8 +/- 2.2 ng x g(-1) tissue) and represents 62% of the total paraben recovered in the extractions. These studies demonstrate that parabens can be found intact in the human breast and this should open the way technically for more detailed information to be obtained on body burdens of parabens and in particular whether body burdens are different in cancer from those in normal tissues.

Carbon nanotube composites

Abstract: Carbon nanotubes are molecular-scale tubes of graphitic carbon with outstanding properties. They are among the stiffest and strongest fibres known, with Young's moduli as high as 1 TPa and tensile strengths of up to 63 GPa. They also have remarkable electronic properties and can be metallic or semiconducting depending on their structure and diameter. There is currently great interest in exploiting these properties by incorporating carbon nanotubes into some form of matrix. A wide range of polymer matrices have been employed, and there is growing interest in nanotube/ceramic and nanotube/metal composites. This review outlines the properties of carbon nanotubes and describes the preparation and properties of carbon nanotube composites. The prospects for commercial exploitation of these materials are discussed.

Risk factors and risk assessment tools for falls in hospital in-patients: a systematic review

Abstract: Objective: to identify all published papers on risk factors and risk assessment tools for falls in hospital inpatients. To identify clinical risk assessment tools or individual clinical risk factors predictive of falls, with the ultimate aim of informing the design of effective fall prevention strategies. Design: systematic literature review (Cochrane methodology). Independent assessment of quality against agreed criteria. Calculation of odds ratios and 95% conWdence intervals for risk factors and of sensitivity, speciWcity, negative and positive predictive value for risk assessment tools (with odds ratios and conWdence intervals), where published data sufWcient. Results: 28 papers on risk factors were identiWed, with 15 excluded from further analysis. Despite the identiWcation of 47 papers purporting to describe falls risk assessment tools, only six papers were identiWed where risk assessment tools had been subjected to prospective validation, and only two where validation had been performed in two or more patient cohorts. Conclusions: a small number of signiWcant falls risk factors emerged consistently, despite the heterogeneity of settings namely gait instability, agitated confusion, urinary incontinence/frequency, falls history and prescription of ‘culprit’ drugs (especially sedative/hypnotics). Simple risk assessment tools constructed of similar variables have been shown to predict falls with sensitivity and speciWcity in excess of 70%, although validation in a variety of settings and in routine clinical use is lacking. Effective falls interventions in this population may require the use of better-validated risk assessment tools, or alternatively, attention to common reversible falls risk factors in all patients.

A Phylogenetic Mixture Model for Detecting Pattern-Heterogeneity in Gene Sequence or Character-State Data

Abstract: We describe a general likelihood-based 'mixture model' for inferring phylogenetic trees from gene-sequence or other character-state data. The model accommodates cases in which different sites in the alignment evolve in qualitatively distinct ways, but does not require prior knowledge of these patterns or partitioning of the data. We call this qualitative variability in the pattern of evolution across sites "pattern-heterogeneity" to distinguish it from both a homogenous process of evolution and from one characterized principally by differences in rates of evolution. We present studies to show that the model correctly retrieves the signals of pattern-heterogeneity from simulated gene-sequence data, and we apply the method to protein-coding genes and to a ribosomal 12S data set. The mixture model outperforms conventional partitioning in both these data sets. We implement the mixture model such that it can simultaneously detect rate- and pattern-heterogeneity. The model simplifies to a homogeneous model or a rate-variability model as special cases, and therefore always performs at least as well as these two approaches, and often considerably improves upon them. We make the model available within a Bayesian Markov-chain Monte Carlo framework for phylogenetic inference, as an easy-to-use computer program.

Factors contributing to the summer 2003 European heatwave

Abstract: Europe was exceptionally warm and dry from May through to the end of August 2003. Figure 1 shows the European average surface air temperature (at 2m) derived from global analyses of the European Centre for Medium-range Weather Forecasts (ECMWF). The analyses are calculated for every 6 hour period at 00, 06, 12 and 18UTC. The daily average is also shown for comparison with the daily climatology for 1958-2002 obtained from the ECMWF re-analysis project (ERA-40; Simmons and Gibson, 2000). The heatwaves in June and early August can readily be identified. During these periods even the night-time temperatures exceeded the climatological daily averages! Averaging over each month, Fig. 7 below shows that the temperature anomalies were 4.2°C in June, 3.8°C in August and almost 2°C in May and July. The temperature anomalies were most extreme in France and Switzerland although maximum temperature records were broken in many parts of Europe. For example, Schar et al (2004) have shown that the June-July-August (JJA) temperature averaged for four Swiss stations exceeded the 1864-2000 mean by 5.1°C, far greater than the next highest anomaly of 2.7°C in 1947. Both Beniston (2004) and Schar et al (2004) argue that a repeat of the 2003 summer would be extremely unlikely if stationarity in the past statistics were to be assumed, but that the temperatures experienced across Europe in summer 2003 could be considered "normal" by the end of the 21 century under a high greenhousegas emissions scenario. Given the increased human mortality experienced during the 2003 heatwave (WHO, 2003; Kovats et al, 2004), this has important implications for future human health.

The Bayesian revolution in genetics

Abstract: Bayesian statistics allow scientists to easily incorporate prior knowledge into their data analysis. Nonetheless, the sheer amount of computational power that is required for Bayesian statistical analyses has previously limited their use in genetics. These computational constraints have now largely been overcome and the underlying advantages of Bayesian approaches are putting them at the forefront of genetic data analysis in an increasing number of areas.

Reconstructing Past Climate from Noisy Data

Abstract: Empirical reconstructions of the Northern Hemisphere (NH) temperature in the past millennium based on multiproxy records depict small-amplitude variations followed by a clear warming trend in the past two centuries. We use a coupled atmosphere-ocean model simulation of the past 1000 years as a surrogate climate to test the skill of these methods, particularly at multidecadal and centennial time scales. Idealized proxy records are represented by simulated grid-point temperature, degraded with statistical noise. The centennial variability of the NH temperature is underestimated by the regression-based methods applied here, suggesting that past variations may have been at least a factor of 2 larger than indicated by empirical reconstructions.

Cellulose microfibril angle in the cell wall of wood fibres

Abstract: The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.

The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming

Abstract: A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO2 is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO2 was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO2 contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO2 and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.

Phylogenomics of Eukaryotes: Impact of Missing Data on Large Alignments

Abstract: Resolving the relationships between Metazoa and other eukaryotic groups as well as between metazoan phyla is central to the understanding of the origin and evolution of animals. The current view is based on limited data sets, either a single gene with many species (e.g., ribosomal RNA) or many genes but with only a few species. Because a reliable phylogenetic inference simultaneously requires numerous genes and numerous species, we assembled a very large data set containing 129 orthologous proteins ( approximately 30,000 aligned amino acid positions) for 36 eukaryotic species. Included in the alignments are data from the choanoflagellate Monosiga ovata, obtained through the sequencing of about 1,000 cDNAs. We provide conclusive support for choanoflagellates as the closest relative of animals and for fungi as the second closest. The monophyly of Plantae and chromalveolates was recovered but without strong statistical support. Within animals, in contrast to the monophyly of Coelomata observed in several recent large-scale analyses, we recovered a paraphyletic Coelamata, with nematodes and platyhelminths nested within. To include a diverse sample of organisms, data from EST projects were used for several species, resulting in a large amount of missing data in our alignment (about 25%). By using different approaches, we verify that the inferred phylogeny is not sensitive to these missing data. Therefore, this large data set provides a reliable phylogenetic framework for studying eukaryotic and animal evolution and will be easily extendable when large amounts of sequence information become available from a broader taxonomic range.

Microbial-gut interactions in health and disease. Prebiotics.

Abstract: In nutritional sciences there is much interest in dietary modulation of the human gut. The gastrointestinal tract, particularly the colon, is very heavily populated with bacteria. Most bacteria are benign; however, certain gut species are pathogenic and may be involved in the onset of acute and chronic disorders. Bifidobacteria and lactobacilli are thought to be beneficial and are common targets for dietary intervention. Prebiotic is a non-viable food ingredient selectively metabolized by beneficial intestinal bacteria. Dietary modulation of the gut microflora by prebiotics is designed to improve health by stimulating numbers and/or activities of the bifidobacteria and lactobacilli. Having an 'optimal' gut microflora can increase resistance to pathogenic bacteria, lower blood ammonia, increase stimulation of the immune response and reduce the risk of cancer. This chapter examines how prebiotics are being applied to the improvement of human health and reviews the scientific evidence behind their use.

Effect of information about benefits of biotechnology on consumer acceptance of genetically modified food: evidence from experimental auctions in the United States, England, and France

Abstract: This study investigates the effect of information about potential benefits of biotechnology on consumer acceptance of genetically modified (GM) foods. Consumer willingness to accept compensation to consume a GM food was elicited using an incentive compatible auction mechanism in three US states (California, Florida, and Texas) and in two European countries (England and France). Results indicate that information on environmental benefits, health benefits and benefits to the third world significantly decreased the amount of money consumers demanded to consume GM food; however, the effect of information varied by type of information and location. Consistent with prior research, we find that initial attitudes toward biotechnology have a significant effect on how individuals responded to new information.

The semi‐direct aerosol effect: Impact of absorbing aerosols on marine stratocumulus

Abstract: SUMMARY Aerosols that absorb solar radiation may lead to a decrease of low-cloud cover and liquid-water path (LWP), leading to a positive radiative forcing. A large-eddy model was used to investigate this ‘semi-direct effect’ for marine stratocumulus and examine the dependency on the vertical distribution of the aerosol. In this study, the aerosols influenced clouds by directly altering the short-wave heating rate (the semi-direct effect), but did not interact with the cloud microphysics (i.e. indirect aerosol effects are excluded). Absorbing aerosols within the boundary layer (BL) decreased LWP by 10 g m −2 , leading to a positive semi-direct forcing. Even for mildly absorbing aerosols (mid-visible single-scattering albedo of 0.96), the semi-direct forcing was three times stronger, and opposite in sign, to the aerosol direct forcing. The semi-direct forcing was found to be proportional to aerosol single-scattering co-albedo (tested to a value of 0.12). Conversely, with the absorbing aerosol layer above the cloud, the LWP increased by 5 to 10 g m −2 , leading to a negative semi-direct forcing. Absorbing aerosols located in the BL heat the cloud layer, enhancing the daytime decoupling and thinning of the stratocumulus layer. Absorbing aerosols immediately above the BL increased the contrast in potential temperature across the inversion, leading to a lower cloud-top entrainment rate. With aerosol both within and above the BL, the semidirect forcing was positive but half the magnitude of that experienced when aerosol was only in the BL. As marine stratocumulus covers about 20% of the globe, the semi-direct effect could significantly influence the radiative forcing by absorbing aerosols.