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Ice sheets may have already passed point of no return

On the edge <i>(Image: Christophe Boisvieux/Hemis FR/Getty Images)</i>

THE cracks are beginning to show. Greenland’s ice sheets slid into the sea 400,000 years ago, when Earth was only a little warmer than it is today. That could mean we are set for a repeat performance.

The finding, along with data from Antarctica, suggests both of Earth’s big ice sheets may have already passed a crucial tipping point, condemning them to collapse – either melting, or sliding into the ocean. That will mean sea levels rising by as much as 13 metres, leading to massive coastal flooding. So how fast will the ice collapse, and can we stop it?

Rising seas are an inevitable consequence of global warming as warmer water expands. But the big risk comes from the ice sheets of Greenland and Antarctica, which contain enough ice to force the oceans up by tens of metres if they melt completely. The Intergovernmental Panel on Climate Change has estimated that sea levels could rise by a metre this century, and that will just be the start.

The obvious danger is that low-lying coastal areas will be gradually swamped. That includes many major cities, such as New York, London and Rio de Janeiro. In the long run, we will have to choose between protecting them with elaborate sea defences or abandoning them to move inland. But long before that, rising seas will make coastal flooding worse. The deluge that swept through New York when superstorm Sandy struck in 2012Movie Camera was worsened by sea level rise, as were the floods caused by typhoon Haiyan in the Philippines last year.

Now a team led by Alberto Reyes of the University of Wisconsin-Madison has evidence that the southern Greenland ice sheet melted during a relatively warm spell that interrupted the ice age. If they are right, the planet may already be warm enough to unleash a collapse.

Short of a time machine, we cannot see how big the Greenland ice sheet was in the past. But ice sheets grind away the rock they sit on, dumping sediment into the sea. So Reyes’s team studied a sediment core that had been drilled out of the Eirik Drift, a sandy hummock in the sea south of Greenland. The core contained sediments laid down over 440,000 years that chemical analysis showed came from Greenland. But hardly any sediment was deposited around 400,000 years ago, for a period of about 10,000 years, suggesting that at this time there was no ice sheet on Greenland to break up the rocks (Nature, DOI: 10.1038/nature13456).

“Our study provides the first evidence that the southern Greenland ice sheet has collapsed in the geologically recent past,” says team member Anders Carlson of Oregon State University in Corvallis.

Indirect evidence suggested the ice sheet shrank considerably back then, but there was always a question mark, says Richard Alley of Penn State University in University Park. “I would probably take the question mark off now.”

This is the latest in a flurry of work suggesting that Greenland’s ice is vulnerable. For instance, better mapping of the bedrock has revealed that the valleys in which the glaciers sit extend further inland, and deeper below sea level, than previously thought. That means warm sea water can creep many kilometres inland, melting the glaciers from beneath (Nature Geoscience,

All this means Greenland’s ice may be on course for full-scale melting. But it is difficult to pin down the temperature tipping point when a collapse becomes inevitable. “We might pass it before we know,” says Alley. We don’t know how much warmer Earth was 400,000 years ago. “It may have been as little as 1 °C warmer than present,” Carlson says.

News from the other end of the planet is no better. While most of Antarctica’s ice appears to be safe, the western fringes may have already passed a point of no return. Several west Antarctic glaciers have retreated by tens of kilometres (Geophysical Research Letters, If west Antarctica’s ice sheet does collapse, it will mean metres of sea level rise.

“We can only hope it takes a long time to happen,” says Tim Lenton of the University of Exeter, UK. The word “collapse” implies a sudden process, butin human terms ice sheets disappear slowly. In the case of Greenland, it will probably take centuries, says Alley. That’s because friction with the underlying rock slows ice flow into the sea, setting speed limits.

But Antarctica’s sheets may melt faster. Its valleys open out into much wider canyons than those in Greenland, so the ice feels less friction. “There remains a chance that west Antarctica doesn’t listen to the speed limits,” says Alley.

Can we stop the ice sheets collapsing? Some suggest cooling the planet by reflecting sunlight back into space, a controversial idea known asgeoengineering. But it might not help the ice, says Lenton, as much of the melting is caused by warm sea water and that takes a long time to cool.

The best option is to stop emitting greenhouse gases, and then start removing them from the atmosphere, says Lenton. “We might be able to get back under the threshold in a couple of centuries,” he says. “Even if you can’t stop the meltdown you could slow it.” That might sound like admitting defeat, but every year we postpone the meltdown is another year in which to get ready for it, he says.

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Monster collision in space: Four clusters of galaxies are smashing into each other

BOSTON — A galactic pileup is underway 5 billion light-years from Earth. The colossal collision is spewing charged particles. And this fountain is huge. It’s jetting particles at nearly the speed of light some 2.5 million light-years into intergalactic space. One might think of the event as building a powerful particle accelerator — one up to a million times as strong as Earth’s mightiest (the Large Hadron Collider).

Astronomers reported the intergalactic fireworks at the American Astronomical Society meeting, here, on June 3. They observed the smashup in new images compiled by two telescopes. NASA’s Chandra X-ray Observatory, a satellite system, eyed the event from an altitude of 139,000 kilometers (86,500 miles) above Earth’s surface. A radio telescope, the Very Large Array, homed in on the collision from the ground. Its 27 antennas are splayed out across the New Mexico desert.

And the source of all the commotion? Four clusters of galaxies are crashing into each other. Together, they involve a mass equal to 3 million billion suns.

Galaxy clusters are the largest structures in the universe that are linked by gravity, notes Reinout van Weeren. He works at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Large clusters can house thousands of galaxies. Astronomers think these built up over billions of years as smaller clusters merged. 

The newly imaged jet sits at the heart of “the most complex cluster collision known,” van Weeren says. Chandra images show gas between the galaxies has been squeezed and heated to 100 million degrees Celsius. Radio maps from the Very Large Array reveal the particle fountain within the hot gas. That jet could provide information about how such large clusters are built.

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First mega-Earth found

The giant exoplanet, Kepler-10c, doesn’t play by the rules. It has as much mass as Neptune — yet it’s made of rock, just like Earth. Astronomers are now calling it a “mega-Earth.” Our solar system’s massive planets, such as Jupiter and Saturn, are made from gas. And scientists used to think any planet that massive must also be made primarily of helium and hydrogen. But Kepler-10c is now forcing experts to throw such assumptions out the window.

Kepler-10c is one of two planets orbiting a sunlike star 564 light-years away. It sits in the constellation Draco. Although as massive as Neptune, this heavyweight is only 2.5 times as wide as Earth. (Neptune’s diameter, for comparison, is 22.4 times that of Earth’s.) So Kepler-10c is dense and its gravity exceptionally strong — about three times stronger than Earth’s, explains David Latham. He’s an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Latham shared his team’s findings June 2 at an astronomy meeting in Boston.

All that mass would give the exoplanet extreme gravity, the researchers note. Kepler-10c also orbits close to its star — so close that it completes an orbit in only 45 days. This proximity to its sun means the planet’s climate also should be brutally hot. (A companion planet, called Kepler-10b, orbits even closer and faster. Earth, by comparison, takes a little more than 365 days to complete one orbit of the sun.)

Kepler-10c was one of the first exoplanets found by the Kepler space telescope. The robotic space mission has been searching for planets beyond our solar system since 2009. Astronomers measured the size of Kepler-10c three years ago. But until now, they didn’t realize its heft.

To measure the mass of an exoplanet, astronomers focus on its sun. A star’s gravity keeps a planet moving in orbit, like Earth moves around our sun. But a planet’s gravity also tugs on the star — and causes the star to wobble. The more mass a planet has, and the closer it is to the star, the more it makes that star wobble. By measuring this stellar wobble, scientists can estimate a planet’s mass. That’s what Latham and his colleagues did with Kepler-10c.

Once they had measured its mass and size, the scientists determined the planet’s density. Density is calculated by dividing mass by volume. Rocky planets are dense: They pack a lot of stuff into a small space. Gas giants aren’t: They are large and fluffy. Latham and his team have now determined that Kepler-10c has the density of rock.

The planet weighs 17 times as much as Earth. Astronomers used to think that planets with at least 10 times the mass of Earth had to be gas giants. As Kepler-10c now shows, that’s not always true. Astronomers have no idea how the rule-breaking planet formed.

Even though Kepler-10c is the only mega-Earth known, it’s probably not the only one out there.

“When one type of planet is found, that’s usually the tip of the iceberg,” says Sara Seager. She’s an exoplanet hunter at the Massachusetts Institute of Technology, in Cambridge, who did not work on the new study. “There are probably many, many more of them,” she says of mega-Earths.

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Seeing red: North’s CO2 hits new peak

April 2014 was the first month in recorded history where average carbon-dioxide levels across the northern half of the world measured at least 400 parts per million (ppm) in air. A United Nations agency reported the new record on May 26.

High above Earth’s surface, carbon dioxide acts as what physicists call a greenhouse gas. The term gets its name from the fact that like the window on a greenhouse, this gas allows sunlight to pass through to the lower atmosphere and ground, where it heats things up. All of that heat, which radiates in the form of infrared energy, would then bounce back into space — except that greenhouse gases trap much of it near to Earth’s surface. This helps keep the planet from being freezing cold, year-round. But there can be too much of a good thing. And the growing excess of carbon dioxide has led to a slowly growing fever, what scientists call global warming.

Climate scientists first recorded the troubling high in carbon dioxide in the Arctic in 2012. Then Hawaii registered a similar peak last year. But until now, the rest of the globe had yet to consistently hit the high mark, notes the United Nation’s World Meteorological Organization, or WMO. The 400 ppm level is largely symbolic. Nothing magic happens at that value. It simple represents a troubling milestone. This CO2 value is nearly 50 percent higher than before the Industrial Revolution, almost two centuries ago. More importantly, the WMO points out, the planet has not seen CO2 levels this high in more than 800,000 years.

And scientists expect CO2 levels to continue rising. One reason: Once a molecule of this gas makes it high into the atmosphere, it will remain there for an average of 100 years. Many other greenhouse gases, by contrast, have far shorter lifetimes. They tend to persist only days to perhaps as long as 12 years.

As such, the Northern Hemisphere’s month-long record CO2 high should sound an alarm about addressing emissions, the WMO contends. From 2002 to 2012, it notes, CO2 was responsible for 85 percent of the total increase in the atmosphere’s heat-trapping ability. 

“If we are to preserve our planet for future generations, we need urgent action to curb new emissions of these heat trapping gases,” said WMO Secretary-General Michel Jarraud. “Time is running out.”

Researchers now expect that within a year or two, the entire globe will experience CO2 levels averaging 400 ppm or higher.

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Explainer: How a fossil forms

Most times, when a living thing dies, it just rots. It leaves no trace that it was ever there. But when the conditions are just right, a fossil may form.

For this to happen, the organism typically must first become quickly buried in sediment on the floor of the sea or some other body of water. Sometimes it may even land in something like a sand dune. Over time, more and more sediments will pile atop it. Eventually compressed under its own weight, this growing accumulation of sediment will transform into hard rock.

Most organisms buried in that rock will eventually dissolve. Minerals may replace any bone, shell or once-living tissue. Minerals also may fill in the spaces between these hard parts. And so a fossil is born.

Some of these fossils contain important information about how an animal lived or died. Or they might even provide clues to ancient climate.


Geologist Julie Codispoti holds a rock containing fossilized Glossopteria leaves. This Antarctic find is part of the Polar Rock Repository — a special lending library on the Ohio State University campus in Columbus.


Fossils come in other forms, too. They can be any trace of an ancient living thing. For instance, scientists consider ancient, preserved footprints and burrows to be fossils. For these trace fossils to form, the impression they make on sediment has to quickly harden or get buried in sediment and remain undisturbed until it can be transformed into rock. Even animal poop can form trace fossils, called coprolites.

Most people associate fossils with animals. But plants and other types of organisms also can leave preserved traces. And they tend to form in much the same way as animal fossils. A special type of fossil is called petrified wood. It forms in the same way as do fossils of dinosaurs or other creatures. They often look similar to real wood, though. In this case, colorful minerals have moved in and replaced tree tissue.

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China battles to be first ecological civilisation

SO YOU want to live in a country that is guided by a philosophy of “ecological civilisation”, run by people with the vision to implement policies that will benefit their children even if it costs more in the short term? Move to China.

Smog gets in your eyes <i>(Image: Aly Song/Reuters)</i>

Not convinced? Last week, news circulated that China is considering limiting its greenhouse gas emissions so that they peak in 2030, followed by an orchestrated fall.

It was one man’s view, expressed at a Beijing conference, not an official announcement. But He Jiankun is chairman of China’s Advisory Committee on Climate Change, and his words are in line with actions China is now taking to address global warming.

“China is already doing a lot,” says Fergus Green of the London School of Economics. “They are probably making the most progress of any country, given that they are starting from a position that is far more challenging.”

“Things are changing very, very fast,” says Changhua Wu of The Climate Group think tank in Beijing.

To be clear, China is still the biggest emitter of carbon dioxide. Cities like Beijing are plagued by smog, and efforts to clean them up may just move the pollution elsewhere. But there is a huge push for change.

Water scarcity and awareness that China will suffer from global warming are factors, but it is health concerns that loom large. The air in many cities is dangerous to breathe, the water is toxic and there are often food health scares. “People are fed up,” says Wu.

Premier Li Keqiang has declared a “war on pollution”. His leadership has drawn up a philosophical framework called ecological civilisation. It aims to “bring everything back to the relationship between man and nature”, says Wu, and is driving major changes.

Prompted by the idea that used resources must be paid for, China has launched carbon trading schemes in six areas. There, companies must pay to pollute, and abide by a cap on overall emissions. A seventh scheme should start within weeks. They will form the world’s second largest carbon trading scheme, after Europe’s. A national programme should begin this decade.

China has set targets to make more wealth using less energy and it is on course to meet them. It contributes one-fifth of global investment in renewables, more than any other nation, has more installed wind power than anywhere else and in 2013 doubled its solar capacity.

The smog is turning people off dirty power. Construction of coal-fired power stations peaked in 2007 (see graph), and smaller power stations are being switched off. According to the London-based think tank Carbon Tracker, 10 out of 30 provinces have cut their coal use, and wind capacity is growing twice as fast as coal. “The coal-fired power plants that China is building are some of the most high-tech and efficient available,” says Carbon Tracker’s Luke Sussams. There are also schemes in place to make people who pollute water pay those who suffer as a result.

Environmentalists have pushed policies like these for years. But while Western nations debate them, China is testing them and rolling out those that work.

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‘Angry alien’ in packing puzzle shocks mathematicians

When it comes to packing, you can’t beat a mathematician. Centuries of work has gone into finding the most efficient ways to pack identical objects into the densest possible arrangements. But the latest experiment shows that a surprising amount of chaos lurks within our attempts to create order.

Easier packing <i>(Image: Sipa Press/Rex)</i>

Sharon Glotzer at the University of Michigan in Ann Arbor and her colleagues started with three distinct shapes: a cube, a 12-sided dodecahedron and a 4-sided pyramid, or tetrahedron. First they created variations of each by slicing off corners, edges or both, until they had more than 55,000 shapes. “We wanted to look at a large enough set of shapes that we could start to see some trends that you can’t get from looking at a couple of shapes,” says Glotzer.

The team then used computer simulations to create identical copies of each new shape and pack them in the most efficient way possible. Finally, they displayed the results for the three shape “families” as three-dimensional landscapes, with changes in height corresponding to packing efficiency.

The team thought small changes to a shape would only gradually affect how it packs, meaning each landscape should be made up of gentle hills. That is the case for the dodecahedron family, but the landscape is bumpy and chaotic for variants of cubes and tetrahedrons. The 3D tetrahedron landscape, shown below from multiple angles, is so weird that the researchers nicknamed it the angry alien, seen best at the bottom left.

(Image: Elizabeth R. Chen, Daphne Klotsa et al)

Real-world objects are likely to have minor defects that change their shapes in similar ways. That means a better understanding of packing variations could be important for nanotech materials built from small particles, or for pharmaceuticals in which the density of a drug matters.

“I believe this research has tremendous value for designing new materials based on nanoparticles,” says Oleg Gang at Brookhaven National Laboratory in Upton, New York. “It gives us a complete understanding of how particles of different shapes pack in larger-scale organisations. Many practical applications, from catalysis to batteries, depend on particle packing.”

Tomaso Aste at University College London also thinks the results could prove useful, but he adds that they need to be double-checked. Packing is a difficult problem, he says, and different computer simulations might find better or worse packing densities for particular shapes, which could alter the landscape.