[Show abstract][Hide abstract] ABSTRACT: Reither et al. (2009) use a Hierarchical Age-Period-Cohort model (HAPC - Yang & Land, 2006) to assess changes in obesity in the USA population. Their results suggest that there is only a minimal effect of cohorts, and that it is periods which have driven the increase in obesity over time. We use simulations to show that this result may be incorrect. Using simulated data in which it is cohorts, rather than periods, that are responsible for the rise in obesity, we are able to replicate the period-trending results of Reither et al. In this instance, the HAPC model misses the true cohort trend entirely, erroneously finds a period trend, and underestimates the age trend. Reither et al.’s results may be correct, but because age, period and cohort are confounded there is no way to tell. This is typical of age-period-cohort models, and shows the importance of caution when any APC model is used. We finish with a discussion of ways forward for researchers wishing to model age, period and cohort in a robust and non-arbitrary manner.
[Show abstract][Hide abstract] ABSTRACT: Climate impact studies focused on the projection of changing flood risk are increasingly utilized to inform future flood risk policy. These studies typically use the output from global (GCMs) and regional climate models (RCMs). However the direct application of GCM/RCM output is controversial as often significant biases exist in predicted rainfall; instead a number of alternative ‘correction’ approaches have emerged. In this study an ensemble of RCMs from the ENSEMBLES and UKCP09 projects are applied, via a number of application techniques, to explore the possible impacts of climate change on flooding in the Avon catchment, in the UK. The analysis is conducted under a continuous simulation methodology, using a stochastic rainfall generator to drive the HBV-light rainfall run-off model under a parameter uncertainty framework. This permitted a comparison between the projections produced by differing application approaches, whilst also considering the uncertainty associated with flood risk projections under observed conditions.
The results from each of the application approaches project an increase in annual maximum flows under the future (2061–2099) climate scenario. However the magnitude and spread of the projected changes varied significantly. These findings highlight the need to incorporate multiple approaches in climate impact studies focusing on flood risk. Additionally these results outline the significant uncertainties associated with return period estimates under current climate conditions, suggesting that uncertainty over this observed record already poses a challenge to develop robust risk management plans.
[Show abstract][Hide abstract] ABSTRACT: This Discussion Meeting Issue of the Philosophical Transactions A had its genesis in a Discussion Meeting of the Royal Society which took place on 10-11 October 2011. The Discussion Meeting, entitled 'Warm climates of the past: a lesson for the future?', brought together 16 eminent international speakers from the field of palaeoclimate, and was attended by over 280 scientists and members of the public. Many of the speakers have contributed to the papers compiled in this Discussion Meeting Issue. The papers summarize the talks at the meeting, and present further or related work. This Discussion Meeting Issue asks to what extent information gleaned from the study of past climates can aid our understanding of future climate change. Climate change is currently an issue at the forefront of environmental science, and also has important sociological and political implications. Most future predictions are carried out by complex numerical models; however, these models cannot be rigorously tested for scenarios outside of the modern, without making use of past climate data. Furthermore, past climate data can inform our understanding of how the Earth system operates, and can provide important contextual information related to environmental change. All past time periods can be useful in this context; here, we focus on past climates that were warmer than the modern climate, as these are likely to be the most similar to the future. This introductory paper is not meant as a comprehensive overview of all work in this field. Instead, it gives an introduction to the important issues therein, using the papers in this Discussion Meeting Issue, and other works from all the Discussion Meeting speakers, as exemplars of the various ways in which past climates can inform projections of future climate. Furthermore, we present new work that uses a palaeo constraint to quantitatively inform projections of future equilibrium ice sheet change.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2013; 371(2001):20130146.
[Show abstract][Hide abstract] ABSTRACT: Geological data for the Early Eocene (56-47.8 Ma) indicate extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data-model differences in the prediction of these polar surface temperatures, resulting in the so-called 'equable climate problem'. In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the Early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations that have an optimal fit with the proxy data. We have simulated the warmth of the Early Eocene at 560 ppmv CO2, which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming. The parameter set from one of the optimal Early Eocene simulations also produces a favourable fit for the last glacial maximum boundary climate and outperforms the control parameter set for the present day. Although this does not 'prove' that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different palaeoclimates and the present-day climate. Interestingly, to achieve the great warmth of the Early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7(°)C, whereas the mean value of the 18 models in the IPCC Fourth Assessment Report (AR4) is 3.26(°)C±0.69(°)C. Thus, this value is within the range and below the mean of the models included in the AR4.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2013; 371(2001):20130123.
[Show abstract][Hide abstract] ABSTRACT: We assess the effect of enhanced basal sliding on the flow and mass budget of the Greenland ice sheet, using a newly developed parameterization of the relation between meltwater runoff and ice flow. A wide range of observations suggest that water generated by melt at the surface of the ice sheet reaches its bed by both fracture and drainage through moulins. Once at the bed, this water is likely to affect lubrication, although current observations are insufficient to determine whether changes in subglacial hydraulics will limit the potential for the speedup of flow. An uncertainty analysis based on our best-fit parameterization admits both possibilities: continuously increasing or bounded lubrication. We apply the parameterization to four higher-order ice-sheet models in a series of experiments forced by changes in both lubrication and surface mass budget and determine the additional mass loss brought about by lubrication in comparison with experiments forced only by changes in surface mass balance. We use forcing from a regional climate model, itself forced by output from the European Centre Hamburg Model (ECHAM5) global climate model run under scenario A1B. Although changes in lubrication generate widespread effects on the flow and form of the ice sheet, they do not affect substantial net mass loss; increase in the ice sheet's contribution to sea-level rise from basal lubrication is projected by all models to be no more than 5% of the contribution from surface mass budget forcing alone.
Proceedings of the National Academy of Sciences 08/2013;
[Show abstract][Hide abstract] ABSTRACT: This study examines the geographical variations of self-rated health of the elderly based on the 2008 Chinese Longitudinal Healthy Longevity Survey. Multilevel logistic models are employed to estimate how individual, family, and institutional factors affect the health of the elderly at both individual and province levels. Results show that while individual characteristics help to explain self-rated health, the family remains an important determinant. Those with nobody to care for them, those in poverty and those who have to rely on medical insurance report the worst health. The role of the state is relatively limited in contributing to the health of the elderly. There are substantial between province differences.
[Show abstract][Hide abstract] ABSTRACT: The idea that the happiness and wellbeing of individuals should shape government policy has been around since the enlightenment; today such thinking has growing practical policy relevance as governments around the world survey their populations in an effort to design social policies that promote wellbeing. In this article, we consider the social determinants of subjective wellbeing in the UK and draw lessons for social policy. Survey data are taken from the 'Measuring National Wellbeing Programme' launched by the UK's Office for National Statistics in 2010. For the empirical strategy, we develop bivariate and multivariate logistic regression models, as well as testing for interaction effects in the data. The findings show that wellbeing is not evenly distributed within the UK. Socio-demographic characteristics such as age, gender, ethnicity, employment, household composition and tenure all matter, as does health status. Influencing population wellbeing is inherently complex, though, that said, there is a clear need to place greater emphasis on the social, given the direction of current policy.
[Show abstract][Hide abstract] ABSTRACT: This commentary discusses the age-period-cohort identification problem. It shows that, despite a plethora of proposed solutions in the literature, no model is able to solve the identification problem because the identification problem is inherent to the real-world processes being modelled. As such, we cast doubt on the conclusions of a number of papers, including one presented here (Page et al., this issue). We conclude with some recommendations for those wanting to model age, period and cohort in a compelling way.
[Show abstract][Hide abstract] ABSTRACT: Previous research has argued that income inequality reduces people's trust in other people, and that declining social trust in the United States in recent decades has been due to rising levels of income inequality. Using multilevel models fitted to data from the General Social Survey, this paper substantially qualifies these arguments. We show that while people are less trusting in US states with higher income inequality, this association holds only cross-sectionally, not longitudinally; since the 1970s, states experiencing larger increases in inequality have not suffered systematically larger declines in trust. For counties, there is no statistically significant relationship either cross-sectionally or longitudinally. There is therefore only limited empirical support for the argument that inequality influences generalized social trust; and the declining trust of recent decades certainly cannot be attributed to rising inequality.
[Show abstract][Hide abstract] ABSTRACT: Randomized controlled trials (RCTs) are increasingly playing a central role in shaping policy for development. By comparison, social experimentation has not driven the great transformation of welfare within the developed world. This introduces a range of issues for those interested in the nature of research evidence for making policy. In this article we will seek a greater understanding of why the RCT is increasingly seen as the 'gold standard' for policy experiments in low-and middle-income countries (LMICs), but not in the more advanced liberal democracies, and we will explore the implications of this. One objection to the use of RCTs, however can be cost, but implementing policies and programmes without good evidence or a good understanding of their effectiveness is unlikely to be a good use of resources either. Other issues arise. Trials are often complex to run and ethical concerns often arise in social 'experiments' with human subjects. However, rolling out untested policies may also be morally objectionable. This article sheds new light on the relationship between evidence and evaluation in public policy in both the global north and developing south. It also tackles emerging issues concerning the 'use' and 'misuse' of evidence and evaluation within public policy.
Social Policy & Administration 01/2013; 47(4):359–381.
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