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Concept: 20th century


We assess the relationship between temperature and global sea-level (GSL) variability over the Common Era through a statistical metaanalysis of proxy relative sea-level reconstructions and tide-gauge data. GSL rose at 0.1 ± 0.1 mm/y (2σ) over 0-700 CE. A GSL fall of 0.2 ± 0.2 mm/y over 1000-1400 CE is associated with ∼0.2 °C global mean cooling. A significant GSL acceleration began in the 19th century and yielded a 20th century rise that is extremely likely (probability [Formula: see text]) faster than during any of the previous 27 centuries. A semiempirical model calibrated against the GSL reconstruction indicates that, in the absence of anthropogenic climate change, it is extremely likely ([Formula: see text]) that 20th century GSL would have risen by less than 51% of the observed [Formula: see text] cm. The new semiempirical model largely reconciles previous differences between semiempirical 21st century GSL projections and the process model-based projections summarized in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.

Concepts: Statistics, Climate change, 20th century, 21st century, Centuries, Intergovernmental Panel on Climate Change, Global warming, 19th century


The disease risks from cigarette smoking increased in the United States over most of the 20th century, first among male smokers and later among female smokers. Whether these risks have continued to increase during the past 20 years is unclear.

Concepts: United States, Smoking, Tobacco, Cigarette, Nicotine, Poverty in the United States, U.S. state, 20th century


Human modification of natural landscapes has influenced surface processes in many settings on Earth. Quantitative data comparing the distribution and behavior of geologic phenomena before and after human arrival are sparse but urgently required to evaluate possible anthropogenic influences on geologic hazards. We conduct field and imagery-based mapping, statistical analysis, and numerical modeling of rockfall boulders triggered by the fatal 2011 Christchurch earthquakes (n = 285) and newly identified prehistoric (Holocene and Pleistocene) boulders (n = 1049). Prehistoric and modern boulders are lithologically equivalent, derived from the same source cliff, and yield consistent power-law frequency-volume distributions. However, a significant population of modern boulders (n = 26) traveled farther downslope (>150 m) than their most-traveled prehistoric counterparts, causing extensive damage to residential dwellings at the foot of the hillslope. Replication of prehistoric boulder distributions using three-dimensional rigid-body numerical models that incorporate lidar-derived digital topography and realistic boulder trajectories and volumes requires the application of a drag coefficient, attributed to moderate to dense slope vegetation, to account for their spatial distribution. Incorporating a spatially variable native forest into the models successfully predicts prehistoric rockfall distributions. Radiocarbon dating provides evidence for 17th to early 20th century deforestation at the study site during Polynesian and European colonization and after emplacement of prehistoric rockfall. Anthropocene deforestation enabled modern rockfalls to exceed the limits of their prehistoric predecessors, highlighting a shift in the geologic expression of rockfalls due to anthropogenic activity. Reforestation of hillslopes by mature native vegetation could help reduce future rockfall hazard.

Concepts: Human, Erosion, Distribution, 20th century, Holocene, Global warming, Geologic time scale, Boulder


Much study has been devoted to the possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming “hiatus.” Here we present an updated global surface temperature analysis that reveals that global trends are higher than reported by the IPCC, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a “slowdown” in the increase of global surface temperature.

Concepts: Temperature, 20th century, 21st century, Global warming


Amazonia is the most biodiverse rainforest on Earth, and the debate over how many tree species grow there remains contentious. Here we provide a checklist of all tree species collected to date, and describe spatial and temporal trends in data accumulation. We report 530,025 unique collections of trees in Amazonia, dating between 1707 and 2015, for a total of 11,676 species in 1225 genera and 140 families. These figures support recent estimates of 16,000 total Amazonian tree species based on ecological plot data from the Amazonian Tree Diversity Network. Botanical collection in Amazonia is characterized by three major peaks, centred around 1840, 1920, and 1980, which are associated with flora projects and the establishment of inventory plots. Most collections were made in the 20th century. The number of collections has increased exponentially, but shows a slowdown in the last two decades. We find that a species' range size is a better predictor of the number of times it has been collected than the species' estimated basin-wide population size. Finding, describing, and documenting the distribution of the remaining species will require coordinated efforts at under-collected sites.

Concepts: Biodiversity, Biology, Species, Tree, 20th century, Brazil, Rainforest, Amazon Rainforest


Examining age, time period, and cohort/generational changes in sexual experience is key to better understanding sociocultural influences on sexuality and relationships. Americans born in the 1980s and 1990s (commonly known as Millennials and iGen) were more likely to report having no sexual partners as adults compared to GenX'ers born in the 1960s and 1970s in the General Social Survey, a nationally representative sample of American adults (N = 26,707). Among those aged 20-24, more than twice as many Millennials born in the 1990s (15 %) had no sexual partners since age 18 compared to GenX'ers born in the 1960s (6 %). Higher rates of sexual inactivity among Millennials and iGen also appeared in analyses using a generalized hierarchical linear modeling technique known as age-period-cohort analysis to control for age and time period effects among adults of all ages. Americans born early in the 20th century also showed elevated rates of adult sexual inactivity. The shift toward higher rates of sexual inactivity among Millennials and iGen'ers was more pronounced among women and absent among Black Americans and those with a college education. Contrary to popular media conceptions of a “hookup generation” more likely to engage in frequent casual sex, a higher percentage of Americans in recent cohorts, particularly Millennials and iGen'ers born in the 1990s, had no sexual partners after age 18.

Concepts: 20th century, Adult


The term parachute trial entered the medical lexicon to depict studies of treatments everyone already assumes to be effective. (In other words, do we need a trial to show that parachutes save the lives of persons who jump from airplanes?(1)) The parachute trial has been invoked to decry randomized trials of total joint replacement as senseless. After all, joint replacements are among the most significant advances of the 20th century; don’t we already know they are successful? Nearly 1 million elective total knee and hip replacements are performed annually in the United States; rates of total knee replacement tripled . . .

Concepts: United States, Osteoarthritis, Hip replacement, Orthopedic surgery, 20th century, Joints, Knee replacement, Autologous chondrocyte implantation


Previous studies have shown that it is possible to detect macroscopic patterns of cultural change over periods of centuries by analyzing large textual time series, specifically digitized books. This method promises to empower scholars with a quantitative and data-driven tool to study culture and society, but its power has been limited by the use of data from books and simple analytics based essentially on word counts. This study addresses these problems by assembling a vast corpus of regional newspapers from the United Kingdom, incorporating very fine-grained geographical and temporal information that is not available for books. The corpus spans 150 years and is formed by millions of articles, representing 14% of all British regional outlets of the period. Simple content analysis of this corpus allowed us to detect specific events, like wars, epidemics, coronations, or conclaves, with high accuracy, whereas the use of more refined techniques from artificial intelligence enabled us to move beyond counting words by detecting references to named entities. These techniques allowed us to observe both a systematic underrepresentation and a steady increase of women in the news during the 20th century and the change of geographic focus for various concepts. We also estimate the dates when electricity overtook steam and trains overtook horses as a means of transportation, both around the year 1900, along with observing other cultural transitions. We believe that these data-driven approaches can complement the traditional method of close reading in detecting trends of continuity and change in historical corpora.

Concepts: Scientific method, Geography, Geographic information system, United Kingdom, Culture, Observation, Menstrual cycle, 20th century


Until the 20th century, home was where most births took place. By the second half of that century, hospital birth had become the norm in most Western countries. With this change came the “medicalization” of birth, as hospitals introduced interventions to reduce the risks inherent to childbirth that could not be performed in the home setting. Many of these interventions were beneficial, even lifesaving, for the mother or baby, but some, often judged in retrospect, seemed unnecessary. The occasional performance of a cesarean delivery for a fetus thought to have hypoxemia and acidosis followed by the delivery of an entirely . . .

Concepts: Pregnancy, Childbirth, Infant, Obstetrics, 20th century, Epidural, Caesarean section, Breech birth


Firearms have been a prevalent cause of morbidity and mortality in the United States since about the turn of the 20th century. Firearm deaths, including homicides, suicides, and unintentional shootings, generally increased from 1900 until the mid-1930s, dipped through the mid-1960s, and rose through the 1990s, reaching a plateau beginning in approximately 2000 that continues to the present. Motor vehicle deaths once far exceeded firearm deaths. However, thanks to investments in research and vehicle and roadway design, motor vehicle deaths have declined substantially and firearm deaths now stand to surpass them. In contrast, there remains a paucity of research about ways in which to mitigate mortality and morbidity caused by firearms. (Am J Public Health. Published online ahead of print January 19, 2017: e1-e3. doi:10.2105/AJPH.2016.303619).

Concepts: Epidemiology, Death, United States, 20th century, Suicide, Firearm, Rifle, Firearms