Archive for the ‘Proceedings of the National Academy of Sciences’ Category

Land, irrigation water, greenhouse gas, and reactive nitrogen burdens of meat, eggs, and dairy production in the United States

July 23, 2014 Comments off

Land, irrigation water, greenhouse gas, and reactive nitrogen burdens of meat, eggs, and dairy production in the United States
Source: Proceedings of the National Academy of Sciences

Livestock-based food production is an important and pervasive way humans impact the environment. It causes about one-fifth of global greenhouse gas emissions, and is the key land user and source of water pollution by nutrient overabundance. It also competes with biodiversity, and promotes species extinctions. Empowering consumers to make choices that mitigate some of these impacts through devising and disseminating numerically sound information is thus a key socioenvironmental priority. Unfortunately, currently available knowledge is incomplete and hampered by reliance on divergent methodologies that afford no general comparison of relative impacts of animal-based products. To overcome these hurdles, we introduce a methodology that facilitates such a comparison. We show that minimizing beef consumption mitigates the environmental costs of diet most effectively.

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Nonlinear permanent migration response to climatic variations but minimal response to disasters

July 3, 2014 Comments off

Nonlinear permanent migration response to climatic variations but minimal response to disasters
Source: Proceedings of the National Academy of Sciences

We present a microlevel study to simultaneously investigate the effects of variations in temperature and precipitation along with sudden natural disasters to infer their relative influence on migration that is likely permanent. The study is made possible by the availability of household panel data from Indonesia with an exceptional tracking rate combined with frequent occurrence of natural disasters and significant climatic variations, thus providing a quasi-experiment to examine the influence of environment on migration. Using data on 7,185 households followed over 15 y, we analyze whole-household, province-to-province migration, which allows us to understand the effects of environmental factors on permanent moves that may differ from temporary migration. The results suggest that permanent migration is influenced by climatic variations, whereas episodic disasters tend to have much smaller or no impact on such migration. In particular, temperature has a nonlinear effect on migration such that above 25 °C, a rise in temperature is related to an increase in outmigration, potentially through its impact on economic conditions. We use these results to estimate the impact of projected temperature increases on future permanent migration. Though precipitation also has a similar nonlinear effect on migration, the effect is smaller than that of temperature, underscoring the importance of using an expanded set of climatic factors as predictors of migration. These findings on the minimal influence of natural disasters and precipitation on permanent moves supplement previous findings on the significant role of these variables in promoting temporary migration.

See: With climate change, heat more than natural disasters will drive people away (EurekAlert!)

Experimental evidence of massive-scale emotional contagion through social networks

July 1, 2014 Comments off

Experimental evidence of massive-scale emotional contagion through social networks
Source: Proceedings of the National Academy of Sciences

Emotional states can be transferred to others via emotional contagion, leading people to experience the same emotions without their awareness. Emotional contagion is well established in laboratory experiments, with people transferring positive and negative emotions to others. Data from a large real-world social network, collected over a 20-y period suggests that longer-lasting moods (e.g., depression, happiness) can be transferred through networks [Fowler JH, Christakis NA (2008) BMJ 337:a2338], although the results are controversial. In an experiment with people who use Facebook, we test whether emotional contagion occurs outside of in-person interaction between individuals by reducing the amount of emotional content in the News Feed. When positive expressions were reduced, people produced fewer positive posts and more negative posts; when negative expressions were reduced, the opposite pattern occurred. These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks. This work also suggests that, in contrast to prevailing assumptions, in-person interaction and nonverbal cues are not strictly necessary for emotional contagion, and that the observation of others’ positive experiences constitutes a positive experience for people.

Economic scarcity alters the perception of race

June 26, 2014 Comments off

Economic scarcity alters the perception of race (PDF)
Source: Proceedings of the National Academy of Sciences

When the economy declines, racial minorities are hit the hardest. Although existing explanations for this effect focus on institutional causes, recent psychological findings suggest that scarcity may also alter perceptions of race in ways that exacerbate discrimination. We tested the hypothesis that economic resource scarcity causes decision makers to perceive African Americans as “Blacker” and that this visual distortion elicits disparities in the allocation of resources. Studies 1 and 2 demonstrated that scarcity altered perceptions of race, lowering subjects’ psychophysical threshold for seeing a mixed-race face as “Black” as opposed to “White.” In studies 3 and 4, scarcity led subjects to visualize African American faces as darker and more “stereotypically Black,” compared with a control condition. When presented to naïve subjects, face representations produced under scarcity elicited smaller allocations than control-condition representations. Together, these findings introduce a novel perceptual account for the proliferation of racial disparities under economic scarcity.

Father’s brain is sensitive to childcare experiences

June 19, 2014 Comments off

Father’s brain is sensitive to childcare experiences
Source: Proceedings of the National Academy of Sciences

Brain, oxytocin, and parenting behavior were measured in primary-caregiving mothers, secondary-caregiving fathers, and primary-caregiving homosexual fathers raising infants without maternal involvement. Parenting integrated functioning of two neural networks: subcortical-paralimbic structures implicated in emotional processing and cortical circuits involved in social understanding. Mothers showed greater activation in the emotional processing network and fathers in the socio-cognitive circuits, which were differentially linked with oxytocin and behavior. Primary-caregiving fathers exhibited high amygdala activation similar to mothers, alongside high superior temporal sulcus (STS) activation comparable to fathers, and functional connectivity between amygdala and STS. Among all fathers, time spent in childcare correlated with amygdala-STS connectivity. Findings describe mechanisms of brain malleability with caregiving experiences in human fathers.

Rate of false conviction of criminal defendants who are sentenced to death

May 7, 2014 Comments off

Rate of false conviction of criminal defendants who are sentenced to death (PDF)
Source: Proceedings of the National Academy of Sciences

The rate of erroneous conviction of innocent criminal defendants is often described as not merely unknown but unknowable. There is no systematic method to determine the accuracy of a criminal conviction; if there were, these errors would not occur in the first place. As a result, very few false convictions are ever discovered, and those that are discovered are not representative of the group as a whole. In the United States, however, a high proportion of false convictions that do come to light and produce exonerations are concentrated among the tiny minority of cases in which defendants are sentenced to death. This makes it possible to use data on death row exonerations to estimate the overall rate of false conviction among death sentences. The high rate of exoneration among death-sentenced defendants appears to be driven by the threat of execution, but most death-sentenced defendants are removed from death row and resentenced to life imprisonment, after which the likelihood of exoneration drops sharply. We use survival analysis to model this effect, and estimate that if all death-sentenced defendants remained under sentence of death indefinitely, at least 4.1% would be exonerated. We conclude that this is a conservative estimate of the proportion of false conviction among death sentences in the United States.

Changing the academic culture: Valuing patents and commercialization toward tenure and career advancement

May 2, 2014 Comments off

Changing the academic culture: Valuing patents and commercialization toward tenure and career advancement (PDF)
Source: Proceedings of the National Academy of Sciences

There is national and international recognition of the importance of innovation, technology transfer, and entrepreneurship for sustained economic revival. With the decline of industrial research laboratories in the United States, research universities are being asked to play a central role in our knowledge-centered economy by the technology transfer of their discoveries, innovations, and inventions. In response to this challenge, innovation ecologies at and around universities are starting to change. However, the change has been slow and limited. The authors believe this can be attributed partially to a lack of change in incentives for the central stakeholder, the faculty member. The authors have taken the position that universities should expand their criteria to treat patents, licensing, and commercialization activity by faculty as an important consideration for merit, tenure, and career advancement, along with publishing, teaching, and service. This position is placed in a historical context with a look at the history of tenure in the United States, patents, and licensing at universities, the current status of university tenure and career advancement processes, and models for the future.

Social disadvantage, genetic sensitivity, and children’s telomere length

April 11, 2014 Comments off

Social disadvantage, genetic sensitivity, and children’s telomere length (PDF)
Source: Proceedings of the National Academy of Sciences

This paper makes two contributions to research on the link between the social environment and health. Using data from a birth cohort study, we show that, among African American boys, those who grow up in highly disadvantaged environments have shorter telomeres (at age 9) than boys who grow up in highly advantaged environments. We also find that the association between the social environment and telomere length (TL) is moderated by genetic variation within the serotonin and dopamine pathways. Boys with the highest genetic sensitivity scores had the shortest TL when exposed to disadvantaged environments and the longest TL when exposed to advantaged environments. To our knowledge, this report is the first to document a gene–social environment interaction for TL, a biomarker of stress exposure.

See: Stressful environments genetically affect African American boys (Science Daily)

Increasing homogeneity in global food supplies and the implications for food security

April 1, 2014 Comments off

Increasing homogeneity in global food supplies and the implications for food security
SOurce: Proceedings of the National Academy of Sciences

The narrowing of diversity in crop species contributing to the world’s food supplies has been considered a potential threat to food security. However, changes in this diversity have not been quantified globally. We assess trends over the past 50 y in the richness, abundance, and composition of crop species in national food supplies worldwide. Over this period, national per capita food supplies expanded in total quantities of food calories, protein, fat, and weight, with increased proportions of those quantities sourcing from energy-dense foods. At the same time the number of measured crop commodities contributing to national food supplies increased, the relative contribution of these commodities within these supplies became more even, and the dominance of the most significant commodities decreased. As a consequence, national food supplies worldwide became more similar in composition, correlated particularly with an increased supply of a number of globally important cereal and oil crops, and a decline of other cereal, oil, and starchy root species. The increase in homogeneity worldwide portends the establishment of a global standard food supply, which is relatively species-rich in regard to measured crops at the national level, but species-poor globally. These changes in food supplies heighten interdependence among countries in regard to availability and access to these food sources and the genetic resources supporting their production, and give further urgency to nutrition development priorities aimed at bolstering food security.

Oxygen requirements of the earliest animals

March 24, 2014 Comments off

Oxygen requirements of the earliest animals
Source: Proceedings of the National Academy of Sciences

A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth’s surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850–542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635–542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5–4.0% present atmospheric levels. Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period. Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans. Instead, other ecological and developmental processes are needed to adequately explain the origin and earliest evolution of animal life on Earth.

Media’s role in broadcasting acute stress following the Boston Marathon bombings

February 18, 2014 Comments off

Media’s role in broadcasting acute stress following the Boston Marathon bombings
Source: Proceedings of the National Academy of Sciences

Media coverage of collective traumas may trigger psychological distress in individuals outside the directly affected community. We examined whether repeated media exposure to the Boston Marathon bombings was associated with acute stress and compared the impact of direct exposure (being at/near the bombings) vs. media exposure (bombing-related television, radio, print, online, and social media coverage) on acute stress. We conducted an Internet-based survey 2–4 wk postbombings with a nationally representative sample and representative subsamples from Boston and New York (4,675 adults). Repeated bombing-related media exposure was associated with higher acute stress than was direct exposure. Media coverage following collective traumas can diffuse acute stress widely. This unique study compares the impact of direct vs. indirect media-based community trauma exposure on acute stress responses.

Coastal flood damage and adaptation costs under 21st century sea-level rise

February 12, 2014 Comments off

Coastal flood damage and adaptation costs under 21st century sea-level rise
Source: Proceedings of the National Academy of Sciences

Coastal flood damages are expected to increase significantly during the 21st century as sea levels rise and socioeconomic development increases the number of people and value of assets in the coastal floodplain. Estimates of future damages and adaptation costs are essential for supporting efforts to reduce emissions driving sea-level rise as well as for designing strategies to adapt to increasing coastal flood risk. This paper presents such estimates derived by taking into account a wide range of uncertainties in socioeconomic development, sea-level rise, continental topography data, population data, and adaptation strategies.

Increasing socioeconomic disparities in adolescent obesity

February 6, 2014 Comments off

Increasing socioeconomic disparities in adolescent obesity
Source: Proceedings of the National Academy of Sciences

Childhood and youth obesity represent significant US public health challenges. Recent findings that the childhood obesity ‘‘epidemic’’ may have slightly abated have been met with relief from health professionals and popular media. However, we document that the overall trend in youth obesity rates masks a significant and growing class gap between youth from upper and lower socioeconomic status (SES) backgrounds. Until 2002, obesity rates increased at similar rates for all adolescents, but since then, obesity has begun to decline among higher SES youth but continued to increase among lower SES youth. These results underscore the need to target public health interventions to disadvantaged youth who remain at risk, as well as to examine how health information circulates through class-biased channels.

Evaluative and hedonic wellbeing among those with and without children at home

January 30, 2014 Comments off

Evaluative and hedonic wellbeing among those with and without children at home
Source: Proceedings of the National Academy of Sciences

We document and interpret differences in life evaluation and in hedonic experience between those who live with children and those who do not; most previous literature has concluded that those with children have worse lives. For a sample of 1.8 million Americans of all ages, and without controls for other circumstances, we find little difference in subjective wellbeing between people with and without children. Among those most likely to be parents, life evaluation and all hedonic experiences except stress are markedly better among those living with a child. However, within this group, people who live with children are more likely to be married, richer, better educated, more religious, and healthier, all of which have well-documented positive associations with evaluative and hedonic wellbeing. With statistical controls for these background factors, the presence of a child has a small negative association with life evaluation, although it is associated with more of both positive and negative hedonics. These patterns are replicated in the English-speaking countries of the world, but not in other regions. We argue that the causal effect of children on parental wellbeing, which is the target for most of the literature, is not well defined. Instead, we interpret our rich-country results within a theory of children and wellbeing in which adults sort into parenthood according to their preferences. In poor, high-fertility countries, we find evidence that at least some people have children even when it diminishes their personal wellbeing.

Small business activity does not measure entrepreneurship

January 23, 2014 Comments off

Small business activity does not measure entrepreneurship
Source: Proceedings of the National Academy of Sciences

Schumpeterian entrepreneurship refers to growing and innovative firms. However, in empirical research the rate of entrepreneurship is commonly estimated using the self-employment rate or other measures of small business activity. We argue that this empirical strategy gives rise to misleading inferences regarding Schumpeterian entrepreneurship. To unambiguously identify this type of entrepreneur we focus on self-made billionaires on Forbes Magazine’s list who became wealthy by founding new firms. We identify 996 such billionaire entrepreneurs in over 50 countries. The rate of billionaire entrepreneurs correlates negatively with self-employment, small business ownership, and startup rates. Countries with higher income, higher trust, lower taxes, more venture capital investment, and lower regulatory burdens have higher entrepreneurship rates but less self-employment.

Multimodel assessment of water scarcity under climate change

December 18, 2013 Comments off

Multimodel assessment of water scarcity under climate change
Source: Proceedings of the National Academy of Sciences

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.

Efficient discovery of overlapping communities in massive networks

December 3, 2013 Comments off

Efficient discovery of overlapping communities in massive networks
Source: Proceedings of the National Academy of Sciences

Detecting overlapping communities is essential to analyzing and exploring natural networks such as social networks, biological networks, and citation networks. However, most existing approaches do not scale to the size of networks that we regularly observe in the real world. In this paper, we develop a scalable approach to community detection that discovers overlapping communities in massive real-world networks. Our approach is based on a Bayesian model of networks that allows nodes to participate in multiple communities, and a corresponding algorithm that naturally interleaves subsampling from the network and updating an estimate of its communities. We demonstrate how we can discover the hidden community structure of several real-world networks, including 3.7 million US patents, 575,000 physics articles from the arXiv preprint server, and 875,000 connected Web pages from the Internet. Furthermore, we demonstrate on large simulated networks that our algorithm accurately discovers the true community structure. This paper opens the door to using sophisticated statistical models to analyze massive networks.

Measurements of methane emissions at natural gas production sites in the United States

December 2, 2013 Comments off

Measurements of methane emissions at natural gas production sites in the United States
Source: Proceedings of the National Academy of Sciences

This work reports direct measurements of methane emissions at 190 onshore natural gas sites in the United States. The measurements indicate that well completion emissions are lower than previously estimated; the data also show emissions from pneumatic controllers and equipment leaks are higher than Environmental Protection Agency (EPA) national emission projections. Estimates of total emissions are similar to the most recent EPA national inventory of methane emissions from natural gas production. These measurements will help inform policymakers, researchers, and industry, providing information about some of the sources of methane emissions from the production of natural gas, and will better inform and advance national and international scientific and policy discussions with respect to natural gas development and use.

Excitable human dynamics driven by extrinsic events in massive communities

October 8, 2013 Comments off

Excitable human dynamics driven by extrinsic events in massive communities
Source: Proceedings of the National Academy of Sciences

Online social networks have over the last decade influenced the way people interact. Data from Twitter allow for a detailed study of the activity in online massive communities. By studying the frequency by which international brands appear on Twitter and the trade of financial securities on financial markets, we find a characteristic bursty behavior of the activity levels of Twitter users and market participants. We explain the bursty behavior by a simple model of the large-scale human behavior and quantify the correlations in the activity levels. The statistical similarity of the two social systems is an indication that the complex process underlying individual decision-making might not be very different for Twitter users and participants in financial markets.

See: Explosive Dynamic Behavior On Twitter and in the Financial Market (Science Daily)

Model projections of atmospheric steering of Sandy-like superstorms

September 30, 2013 Comments off

Model projections of atmospheric steering of Sandy-like superstorms
Source: Proceedings of the National Academy of Sciences

Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multimodel ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast.


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