Article Highlights
 Dimmer switch on global
warming explained
The atmospheric concentration of carbon dioxide increased steadily between 1998 and 2008 even as the Earth?s temperature declined,
consistent with climate change resulting from both natural and human causes, researchers find. Robert Kaufman and colleagues
used model simulations to pinpoint factors that may have triggered a decade-long cooling event during what was otherwise a
period of warming. The study period was part of a normal 11-year cycle of declining solar energy input, according to the authors.
The decade also included a cyclical shift from an El Ni?o pattern to a La Ni?a climate pattern?an ocean-atmosphere phenomenon
that frequently causes cooling. The authors further noted that China doubled its coal consumption from the years 2003 to 2007,
leading to a huge increase in sulfur emissions that may have had a cooling effect on the planet. The researchers suggest that
this cooling effect may have counteracted ongoing warming due to increased carbon dioxide concentrations, permitting natural
forces to predominate the planet?s temperature. The proposed explanation may portend a future period of rapid global warming
as solar input rises and as China installs scrubbers that remove aerosols from coal-fired boilers, according to the authors.
"Reconciling anthropogenic climate change with observed temperature 1998?2008," by Robert K. Kaufmann, Heikki Kauppi, Michael
L. Mann, and James H. Stock
10.1073/pnas.1102467108
[Abstract]
Childbearing and educational achievement
A study finds that the correlation between low birth rate and a woman?s education level may reflect the increased tendency
of childbearing women to leave school or avoid time-intensive higher education. Joel Cohen and colleagues used life-history
information from more than 26,000 Norwegian women, aged 17-39, to model the effects of childbearing on education and, conversely,
the effects of education on childbearing. The researchers estimated the probabilities of an additional birth, a change in
education level, and of academic enrollment in the coming year for a given fertility history, attained education, and enrollment
history. Using a simple model, the researchers found that childbearing impeded education much more than education impeded
childbearing. The researchers caution that childbearing decisions are more complicated than assumed in the model, and that
the results might have varied if other influencing factors were taken into account. The authors suggest that the results,
if confirmed elsewhere, may encourage policymakers to encourage educational gains by informing potential mothers of the educational
impacts of childbearing or by reducing the cost of child care for student mothers.
"Childbearing impeded education more than education impeded childbearing among Norwegian women," by Joel E. Cohen, ?ystein
Kravdal, and Nico Keilman
10.1073/pnas.1107993108
[Abstract]
Gut tells brain to overeat
fatty foods
Researchers may have identified a key component of the brain?s reward circuitry that hardwires mammals to overeat fatty foods,
according to a study. Most mammals have evolved an innate preference for fat-rich foods, which are nutritionally essential
but scarce in most natural habitats. The predilection helps animals survive in the wild, but this gorging contributes to obesity,
diabetes, and cardiovascular disease in industrialized societies, where humans have unrestricted access to fatty foods. Daniele
Piomelli and colleagues conducted a study to determine
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whether neurotransmitters produced in the gut, known as endocannabinoids, help regulate dietary fat intake. According to the
authors, rats that
were allowed to consume, but not digest, a fatty meal had higher levels
of endocannabinoids in their guts, compared with rats fed sugary and high-protein meals. Oral receptors, the authors report,
stimulate the production of endocannabinoids in the gut, which in turn reinforce positive feedback in the brain that can lead
to overeating. The findings suggest that drug therapies designed to curb endocannabinoid activity in the gut can potentially
reduce the desire to preferentially consume fat-rich foods, and help prevent the cascade of health problems that can stem
from obesity, according to the authors.
"Endocannabinoid signal in the gut controls dietary fat intake," by Nicholas V. DiPatrizio,
et al.
10.1073/pnas.1104675108
[Abstract]
Bananas? road to domestication
The first stages in the domestication of many bananas consumed today likely occurred in New Guinea, according to a perspective.
Tim Denham and colleagues combined genetic, archaeological, and linguistic data to trace the domestication and spread of bananas
in the Musa family, which includes plantains and the classic yellow bananas found in supermarkets. The authors' genetic analysis showed
that bananas in the islands around Southeast Asia and western Melanesia hybridized into subspecies that could not have formed
without human intervention. Some of those hybrids then likely paired with other subspecies to create sterile varieties ideal
for farming. To trace the spread of those newly emerged bananas, or cultivars, the authors evaluated the microscopic remains
of banana seeds and leaves at archaeological sites in New Guinea and Cameroon and found evidence for banana cultivation. They
then paired the genetic and archaeological data with linguistic information to identify the spread of specific varieties.
Introduced cultivars often retain all or parts of the word used to identify them from the previous locale, so the authors
looked at 1,100 banana descriptors in Southeast Asia and Melanesia. They isolated four key cognates, or linguistic derivations,
each suggestive of a different dispersal trajectory. Bananas remain a staple crop throughout the world, and tracing their
route to domestication could help today?s farmers breed more resilient crops, the authors suggest.
"Multidisciplinary perspectives on banana (Musa spp.) domestication," by
Xavier Perrier, et al.
10.1073/pnas.1102001108
[Abstract]
Also of Interest
Communicating to combat climate change
Researchers use a public goods game to show how early communication strategies could mitigate the inequalities between rich
and poor nations when attempting to combat climate change.
"Inequality, communication, and the avoidance
of disastrous climate change in a public goods game," by Alessandro Tavoni, Astrid Dannenberg, Giorgos Kallis, and Andreas
L?schel
10.1073/pnas.1102493108
[Abstract]
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