Climate change may make civil wars much more common

As the mercury rises, so too will a tide of human violence, according to a new analysis that puts a fresh spin on the phrase .

Indeed, if societies respond to future warming in the same way as they have responded to historical surges in temperature, the frequency of civil wars could increase by more than 50 per cent by the middle of the century.

But this provocative attempt to quantify the influence of climate on human conflict is itself setting off clashes among researchers who study the issue. "I would take their projections with a huge grain of salt," says Halvard Buhuag of the Peace Research Institute Oslo in Norway.

The new study is by economists at the University of California, Berkeley, who sought to make sense of a recent explosion of research into the relationship between climate and conflict. Marshall Burke and his colleagues used a meta-analysis of multiple studies, combining the different findings to try to find definitive answers.

Broad net

The Berkeley researchers cast a broad net, looking at studies of many types of violence – from crimes such as murder and assault, to riots and civil wars – over a broad sweep of human history. They then narrowed the focus to include only studies that used rigorous methods to study the relationship between violence and surges in temperature or changes in rainfall. Where possible, they reanalysed the original data to help studies clear this bar, generating a cohort of 60 studies.

Their results suggest that warming and extremes of rainfall – both drought and deluge – are associated with upswings in violence. The relationship seems stronger for conflicts between groups of people than acts of violence between individuals.

The researchers were also able to estimate the size of the effect. For each standard deviation of warming – a statistical measure of variation from average conditions – they calculate that the frequency of conflicts between groups rises by 14 per cent. Given that inhabited regions could warm by between two and four standard deviations from the current norm by the middle of the century, an alarming surge in conflict could be in store.

Conclusions disputed

Those conclusions are controversial, however. Unlike in medicine, where meta-analyses combine well-controlled experiments conducted using common methods, the Berkeley team crunched numbers from a wide variety of studies that rely on observations of how patterns of violence shift with changing temperature and rainfall.

Given this chequered background, the exact criteria the team used to include or exclude studies may affect the conclusions drawn, critics suggest. "I have some concerns about the selection," says Buhaug, who has previously crossed swords with Burke over an earlier study suggesting that global warming will cause a surge in civil wars in Africa.

What's more, the Berkeley team's conclusions come from analysing the consequences of relatively brief departures from average conditions. It doesn't necessarily follow that sustained warming in the coming decades will have the same effect.

"I'm optimistic," says Cullen Hendrix, a conflict specialist at the College of William and Mary in Williamsburg, Virginia. "Unlike glaciers, humans have remarkable adaptive capacity," he says.

Conflict in decline

Trends over the past few decades reinforce this encouraging message, says Idean Salehyan of the department of political science at the University of North Texas, Denton. "We've seen rising temperatures, but there's actually been a decline in armed conflict." That is probably due to factors including economic growth in developing countries and a spread of democracy.

Also under discussion is the mechanism by which warming could give rise to an increase in violence. One leading idea is that extreme conditions cause economic disruptions that drive people into conflict. Burke hopes that the new meta-analysis will prompt further research. "If we can understand it, then we can really think about adaptation and how to help societies respond," he says.

Journal reference: Science, DOI: 10.1126/science.1235367

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Today on New Scientist

Asteroid pinpointed as likely source of Russian meteor

The parent of the Chelyabinsk meteor, which exploded over Russia earlier this year, may have been a known rock cluster that could pose a future threat

What are the options for right-to-die campaigners?

This week, two severely paralysed men received the verdicts in their right-to-die cases at the UK's Court of Appeal. New Scientist unpicks the issues

Super-supernovae spell trouble for dark energy

Some obscenely bright stellar explosions are undermining our attempts to work out why the universe is accelerating

Any cellphone can be traced by its digital fingerprint

Slight differences in cellphone components give every handset an unalterable secret signature – that offers a simple way to track them

Giant clouds of lead glimpsed on distant dwarf stars

A lead balloon is a metaphor for something unpopular, but giant clouds of the heavy metal are helping to boost a theory of star evolution

Earth in miniature: Tour a mini-world under glass

Back in the 1980s, Biosphere 2 was created in Arizona as a trial Mars colony and to study several of Earth's ecosystems. Visit the site on our virtual tour

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Coral mappers reach Caribbean waters

(Image: Coral Reef Photos/Catlin Seaview Survey)

Coral reefs teem with a diverse array of life and colour, but in many places around the world, their future is uncertain. The Caribbean, where this vibrant moray eel was shot by an advance party for the mappers, is having a particularly bad time of it.

Over the past 50 years, 80 per cent of the coral reef cover there has been lost to a perfect storm of pollution, overfishing, rising temperatures and ocean acidification. Researchers worry that others could soon be in a similar state.

More detailed, comparable information on how reefs are faring around the world is vital if we are going to be able to protect them.

One group attempting to do this is the Catlin Seaview Survey. They have already photographed the length of the Great Barrier Reef, and yesterday they announced they are now expanding their efforts into the Caribbean and Bermuda. The pictures and footage they take will be made publicly available and will provide a baseline snapshot that researchers can refer to when looking at how corals have responded to future climate change.

The survey relies on several specialised panoramic cameras, capable of taking multiple pictures at a time every three seconds. The cameras are attached to a motorised scooter steered by a diver, which drives the camera forward.

The camera set-up is 16 times faster than other similar technologies at cataloguing data, says project director Richard Vevers. "We're hoping that it will allow us to map all the world's main coral reefs over a three year period."

Globally, it is estimated that coral reefs help support half a billion people through tourist revenue as well as protecting the shoreline from erosion and storm surges.

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Food stamps could help US trim obesity epidemic

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Interactive graphic: the growth of food stamps

This is the San Francisco that the tourists never see: the Alice Griffith housing project in the neighbourhood of Bayview-Hunters Point is as distressing an example of urban decay as you'll witness anywhere in the US. Housing units are boarded up; broken bottles crunch underfoot; police cars rumble by.

I'm here in the south-east corner of the city with Dana Andrews, who worked as a nutritionist for the local YMCA until a couple of months ago, when multiple sclerosis forced her to quit. Today, like many of her former clients, she has to rely on the federal Supplemental Nutrition Assistance Program (SNAP) for her basic needs. "If I didn't have it, I don't know where I would be," she says.

As the US Congress wrangles over legislation to renew funding for SNAP – generally known as "food stamps" – deep cuts seem likely that will hit these streets especially hard.

Political spin

Listen to some of the political rhetoric, and you would imagine that the cost of feeding nearly 48 million food-stamp recipients is dragging the US economy into the mire. In fact, research by the US Department of Agriculture (USDA) suggests that SNAP stimulates as much as $9 of economic activity for every $5 it spends – knock-on effects that are especially important in depressed neighbourhoods like Bayview-Hunters Point.

What's more, public health advocates say the current political acrimony has obscured a big opportunity: using SNAP to experiment with solutions to the US's wider problems of poor nutrition and obesity.

Because junk food is cheaper than fruit and vegetables, poverty and obesity tend to go hand-in-hand. But even after controlling for this association, some research suggests that recipients of food stamps are more likely to be obese. In a 2010 analysis, for example, Charles Baum of Middle Tennessee State University in Murfreesboro estimated that, for women, receiving food stamps boosts the prevalence of obesity by 13.5 per cent.

This does not mean that SNAP can be blamed for the US obesity epidemic, which is so huge that any increase linked to food stamps would be hard to detect. But it does indicate that there's scope for experimenting with the way in which benefits are delivered to improve the health of the country's poorest citizens.

One simple idea is to give the benefits every two weeks, rather than monthly. This would smooth out a cycle in which people load up on high-calorie food when the payments come in, then go hungry towards the end of the month – a pattern known to cause weight gain. Such a monthly cycle may explain findings like Baum's.

Fruit boost

But most attention is focused on efforts to provide incentives to buy fruit and vegetables, or restrict purchases of junk food. A pilot project delivered promising results last month. Over 14 months to December 2012, 7500 households receiving food stamps in Hampden, Massachusetts, were given an extra 30 cents for every dollar spent on fruit and vegetables. Surveys run four to six months into the study show that their consumption of fruit and vegetables was 25 per cent higher than for people on regular food stamps.

Sanjay Basu of Stanford University in California has studied how changes in food prices affect what people put in their shopping baskets. His work suggests that banning food-stamp purchases of unhealthy foods, or increasing their price, should be even more effective (Medical Decision Making, doi.org/nbf).

But the idea of restricting people's choice is controversial, and influential lobby groups oppose any such change. These include the Food Research and Action Center, the main non-profit group campaigning against hunger in the US, and the Grocery Manufacturers Association, whose members make billions of dollars from purchases made under SNAP. Against this background, the USDA, which backed the Hampden study, has so far denied requests to experiment with restricting purchases of junk food.

Fast food habit

My trip to Bayview-Hunters Point exposed further difficulties. Andrews took me to meet Christine Drummer, who helps run a food pantry in the Alice Griffith Housing Project. She distributes packages of fresh food to local residents – many of them seniors who cannot walk to the nearest supermarket, a mile or so away. Drummer, who lives nearby, is frustrated that more local residents are not making use of the pantry service. "People around here don't know how to cook well," she laments.

That's in large part a consequence of the neighbourhood's long-standing status as a "food desert" – where fast food joints and convenience stores are the main suppliers of food. "If a kid's used to eating fast food, then they're going to adapt to this habit of bad nutrition," Drummer says. Her comments echoed in my mind later as we visited a nearby corner store, when a child who asked Andrews for money to buy a soda turned down her offer of an apple.

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Asteroid pinpointed as likely source of Russian meteor

Who's been taking potshots at Earth? A new study shows how a 200-metre-wide cluster of rocks, first spotted by scientists in 2011, could have spawned the Chelyabinsk meteor which exploded over Russia earlier this year.

If correct, that means we may need to watch out for further impacts from other fragments of the cluster, which are still at large, in orbit around the sun.

The meteor that exploded over Russia on 15 February, scattering debris across the Chelyabinsk region and injuring hundreds , came as a complete surprise. Since then researchers have traced it to the Apollo asteroid family, but no one had matched it to a particular member of the group.

Now Carlos de la Fuente Marcos and his brother Raul, both of the Complutense University of Madrid, Spain, are pointing the finger at asteroid 2011 EO40. Roughly 200 metres wide, it is a rock – or cluster of rocks – previously listed as potentially hazardous by the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts.

Rubble pile

First the pair used a computer simulation to create hypothetical orbital paths around the sun that would have intersected with Earth at the time that the meteor hit. Then they searched a database of known asteroids for ones that could have produced rocks that follow those orbits . The closest match was with 2011 EO40.

Most asteroids aren't solid rocks but rather rock clusters that have been gradually fragmenting for eons. "Most asteroids are rubble piles, very fragile," says Carlos. So the brothers also simulated the disintegration of an object the size of 2011 EO40 and showed that it could fragment to produce a Chelyabinsk-size object that would impact with Earth at the correct time.

Future observations of 2011 EO40 could help confirm it as the Chelyabinsk parent. Analysing the light bouncing off it would let us match its composition to fragments of the meteorite collected in Russia. Sending a probe to bring back samples of the asteroid is the only way to be sure, but that is a hugely expensive mission that is unlikely to happen. "The cheap but not fully conclusive approach will have to suffice for the time being," says Carlos.

Asteroid census

If 2011 EO40 really is Chelyabinsk's parent, future observations should also help us predict if Chelyabinsk has any siblings still in orbit that might also pose a threat to Earth, says Carlos. "Having a precise census of this population can help us predict similar impacts in the future."

Jorge Zuluaga of the University of Antioquia in Colombia, who traced the Chelyabinsk meteor to the Apollo asteroid family, cautions that EO40 2011 has yet to be confirmed as the parent. And even it is, he is not too worried about it spawning further impacts.

"I don't think this particular asteroid is more hazardous than others in the MPC list," he says. He also points out that the asteroid itself isn't on a direct collision course with Earth, in any case.

Meanwhile, other researchers are working to piece together the orbit of the Chelyabinsk meteor by different methods. One recent study by Simon Proud of the University of Copenhagen, Denmark, unearthed satellite pictures that show what the meteor looked like from space as it streaked through our atmosphere (see image).

Journal reference: Monthly Notices of the Royal Astronomical Society Letters, in press

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What are the options for right-to-die campaigners?

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This week two severely paralysed men, Paul Lamb and another known only as Martin, received the verdicts in their right-to-die challenges at the UK's Court of Appeal. The family of the late Tony Nicholson were also in court, appealing the 2012 decision that he did not have the right to ask a doctor to end his life. New Scientist examines the issue of euthanasia and some of its ethics in more detail.

First of all, how are euthanasia and assisted suicide defined?

Euthanasia means "good death" in Greek. It can be subdivided into several categories.

Active euthanasia occurs when someone ends another person's life to relieve their suffering, for example, by injecting them with lethal drugs. Passive euthanasia is when something keeping a person alive is withdrawn or withheld, such as food and water or turning off a life-support machine. If the person concerned is able to give their consent, this is known as voluntary euthanasia.

In non-voluntary euthanasia, a person is unable to give consent, perhaps because they are too young or in a minimally conscious state. Involuntary euthanasia occurs when someone able to give consent is killed against their will, but this is almost always classified as murder. The legal and moral issues surrounding these two forms are usually more clear-cut than for voluntary euthanasia.

Complicating matters further is assisted suicide. This is when a person carries out their own suicide, helped by someone else. An example of this would be handing a person lethal sedatives that they then take.

What is currently allowed under UK law?

Passive euthanasia is legal, active euthanasia is not. "It's legal to withdraw food and water from someone and let them starve or dehydrate, but illegal to actually administer anything that actively kills them," says Richy Thompson of the British Humanist Association. Assisting a suicide is also illegal.

How does this affect Paul Lamb?

Lamb, who was paralysed in car crash in 1990, could refuse food and water and his subsequent death would leave his family in the clear. This was what Nicholson did in 2012 after he lost a High Court case to allow doctors to end his life. But such a drawn-out death is obviously unattractive.

Lamb wanted the court to rule that any medical professional who helped him end his life would not be charged with murder. Yesterday the Court of Appeal rejected this challenge, saying that Parliament, not High Court judges, should decide whether or not to change the law on euthanasia. Lamb now has the right to appeal.

What does Martin want?

Like Nicholson, Martin suffers from locked-in syndrome, which means his mind functions but his body is completely immobile. Martin sought to clarify whether a healthcare professional would be prosecuted if they took him abroad to end his life. His family have said they don't want any involvement.

Currently the laws for healthcare professionals travelling to countries where assisted suicide is legal are ambiguous, and yesterday the High Court agreed that they needed clarification.

Martin's case is similar to that of Debbie Purdy, who has multiple sclerosis and whose 2009 case forced a clarification of the laws for family members who took their relatives abroad to end their lives via assisted suicide. To date, no one who has taken a relative to die abroad has been prosecuted.

What is the law in other countries?

Active voluntary euthanasia is legal under strict guidelines in Belgium, the Netherlands and Luxembourg, but only for residents of those countries. Assisted suicide is legal in Switzerland and in the US states of Oregon, Washington and Vermont.

Why can't Martin go to Dignitas, the Swiss group that helps people carry out assisted suicide?

Martin is still able to swallow so in theory he could visit Dignitas, as he would be able to take the last step that leads to his death. This means the act is classed as assisted suicide rather than active euthanasia, which not legal in Switzerland. A paralysed person who couldn't swallow could not be treated at Dignitas. But existing UK laws mean any healthcare professional who accompanies Martin to Switzerland could potentially be prosecuted.

What is next for Lamb?

Lamb has already been granted the right of appeal in the UK Supreme Court. He has a further option, too, should he be unsuccessful. "It is possible for him to go to the European Court of Human Rights to fight his case," says Jonathan Robinson of Bindmans LLP, the law firm assisting him. What might happen if that tactic also fails is uncertain.

What are the arguments for and against euthanasia and assisted suicide?

Organisations such as the British Humanist Association argue that a person's life is theirs to do with as they wish, and that those such as Paul Lamb who are incapable of taking their own lives still deserve a dignified death.

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Super-supernovae spell trouble for dark energy

WHEN Andy Howell announced what he had found, a gasp filled the lecture hall. "Nobody saw it coming," he says.

That was in Prague in 2006. Howell, now at the University of California, Santa Barbara, was at a meeting of the International Astronomical Union presenting his team's latest observations of the exploding stars known as type-1a supernovae. We think we know what makes these stellar bombs tick – and a lot rides on us knowing it. Above all, they detonate with a similar brightness, a fact that allows us to calibrate distance in the universe. Observations of type-1a supernovae led 15 years ago to one of the landmark discoveries of modern cosmology: that the expansion of the universe is accelerating, fuelled by a shadowy agent since dubbed dark energy.

Except if what Howell was saying was right, things weren't that simple. He and his colleagues had seen ...

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Any cellphone can be traced by its digital fingerprint

Tech-savvy criminals try to evade being tracked by changing their cellphone's built-in ID code and by regularly dumping SIM cards. But engineers in Germany have discovered that the radio signal from every cellphone handset hides within it an unalterable digital fingerprint – potentially giving law enforcers a simple way of tracking the handset itself.

Developed by Jakob Hasse and colleagues at the Technical University of Dresden the tracking method exploits the tiny variations in the quality of the various electronic components inside a phone.

"The radio hardware in a cellphone consists of a collection of components like power amplifiers, oscillators and signal mixers that can all introduce radio signal inaccuracies," Hasse says. A phone's resistance, for instance, can vary between 0.1 and 20 per cent of its stated value depending on the quality of the component.

The upshot of these errors is that when analogue signals are converted into digital phone ones, the stream of data each phone broadcasts to the local mast contains error patterns that are unique to that's phone's peculiar mix of components. In tests on 13 handsets in their lab, the Dresden team were able to identify the source handset with an accuracy of 97.6 per cent.

"Our method does not send anything to the mobile phones. It works completely passively and just listens to the ongoing transmissions of a mobile phone – it cannot be detected," Hasse says.

Their research, funded by the EU and the German government, was performed on 2G phones. But "defects are present in every radio device, so it should also be possible to do this with 3G and 4G phones," Hasse says.

The novel method is welcome but technically demanding, say forensics specialists.

"Serious criminals are extremely adept in using single-use phones and dumping SIM cards so new capabilities like this would certainly help law enforcement," says Nick Furneaux of forensics security company CSItech in Bristol, UK.

"Identifying a phone from its radio frequency fingerprint is certainly not far-fetched. It is similar to identifying a digital camera where the image metadata does not provide a serial number. From underlying imperfections in the lens, which are detectable in the image, the source camera can be identified," Furneaux says.

William Webb, CEO of the UK-based Weightless Special Interest Group , which is engineering ways to use unused TV frequencies for broadband transmission, says the method is plausible but boosting the handset recognition rate to 100 per cent will be the team's overarching challenge. "If they can't do this it could lead to hundreds of thousands of mis-tracked calls, privacy invasions and wrongly disconnected mobiles," he warns.

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Giant clouds of lead glimpsed on distant dwarf stars

A lead balloon may be a metaphor for something unpopular, but real life clouds of lead glimpsed in the atmosphere of two stars are having the opposite effect. The giant clouds – thought to be 100 kilometres thick – are helping to boost a theory of stellar evolution.

Although lead is one of heaviest of the naturally occurring elements, clouds of the stuff were predicted to exist as part of a theory about the origins of a type of star called a hot subdwarf. These stars are about half as massive as our sun, and, unlike our sun, which fuses hydrogen to form helium, burn helium in their cores.

Astronomers think that they form when bloated old red giant stars are stripped of the outer layers of their atmosphere, possibly because of interaction with a lower-mass companion star or even a planet.

What's left behind in the immediate aftermath should be an extremely hot star whose outer layers are rich in helium.

Floating lead

The idea is that the helium, and other light elements heavier than hydrogen, then sink towards the core. And as part of this process of rearrangement, something strange happens to heavy elements. Depending on the star's temperature, ions of heavy metals, including lead, can interact with the light streaming out of the star, causing them to rise to the surface.

"Different ions will experience different forces from light and will float up and down," says Simon Jeffery of the Armagh Observatory in the UK. "Everything starts to sort itself into layers and those layers will migrate up and down depending on the temperature."

The trouble was that until now the only hot subdwarfs glimpsed seemed to be at the end of this process – their atmospheres were made of hydrogen and had only traces of helium or heavy metals.

That changed when a team led Naslim Neelamkodan of the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan, which included Jeffery, glimpsed hot subdwarfs much earlier on in their evolution.

Missing link

When the team examined 134 hot subdwarfs in data collected by the Very Large Telescope in Chile, they found layers of heavy metals in two – one 800 light years from Earth and the other 1000 light years away, and both about seven times hotter than the sun. They discovered the metals by looking at the spectra of light from these stars. For example, the lead ions in the stars' atmospheres were absorbing light, leading to a telltale signature.

The astronomers calculated that lead is 10,000 times more abundant in the atmosphere of these two stars than in the sun's atmosphere. They estimate that the layer of lead is about 100 kilometres thick and weighs 100 billion tonnes.

It wasn't just lead, though. One of the stars also had smaller layers of the heavy metals zirconium and yttrium, which is also predicted by the hot subdwarf theory.

Because the stars' atmospheres are also relatively rich in helium, the team say that they represent a key transition phase between being a red giant to being a normal hot subdwarf, in which most of the helium has settled in the core and the lead clouds have diffused throughout the star. "These stars present a missing link," says Jeffery. That strengthens the theory of subdwarf evolution.

Such stars can collectively be called heavy metal subdwarfs, the team suggests. If only stars could form rock bands.

Journal reference: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stt1091

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Earth in miniature: Tour a mini-world under glass

11:23 01 August 2013

In the late 1980s, in a patch of desert north of Tucson, Arizona, a group of environmentalists built a self-contained miniature world under glass which became home to researchers for a two-year experiment. Called Biosphere 2, it was designed to serve as a trial Mars colony and to enable the researchers to study ecosystems in their entirety. Plants and animals from around the globe were brought in to populate six different biomes, which still exist today. Tiffany O'Callaghan gives us a tour of the site – now open to visitors – which is still being used to gain insight into the original biosphere, Earth.

Read more: "Reality bites: the lessons of Biosphere 2"

Image 1 of 8

When planning Biosphere 2, engineers realised that large temperature swings from day to evening would alter the air pressure inside, and that this could crack the glass enclosure. To cope with the problem, they created two large "lungs" with vast rubber bladders that expand and contract with the changing air pressure.

(Image: David Kadlubowski/Corbis)

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