The Southern Ocean has lost its appetite for carbon dioxide, and now it appears that the ozone hole could be to blame.

In theory, oceans should absorb more CO2 as levels of the gas in the atmosphere rise. Measurements show that this is happening in most ocean regions, but strangely not in the Southern Ocean, where carbon absorption has flattened off. Climate models fail to reproduce this puzzling pattern.

The Southern Ocean is a major carbon sink, guzzling around 15 per cent of CO2 emissions. However, between 1987 and 2004, carbon uptake in the region was reduced by nearly 2.5 billion tonnes – equivalent to the amount of carbon that all the world's oceans absorb in one year.

To figure out what is going on, Andrew Lenton, from the University of Pierre and Marie Curie in Paris, France, and his colleagues created a coupled ocean and atmosphere climate model, to investigate carbon absorption in oceans. Crucially, they included changes in the concentration of stratospheric ozone since 1975.

By running their model with and without the ozone depletion since 1975, Lenton and his colleagues were able to show that the ozone hole is responsible for the Southern Ocean's carbon saturation.

The effect could be down to the way decreasing stratospheric ozone and rising greenhouse gases are altering the radiation balance of the Earth's atmosphere. This has been predicted to alter and strengthen the westerly winds that blow over the Southern Ocean.

"We expected this transition to a windier regime, but it has occurred much earlier than we thought, seemingly because of the ozone hole," says Lenton.
'Unexpected effect'

Stronger surface winds enhance circulation of ocean waters, encouraging carbon-rich waters to rise from the deep, limiting the capability of surface water to absorb carbon from the atmosphere. Furthermore, the higher carbon levels in surface waters make them more acidic – bad news for many forms of ocean life, such as coral and squid.

"This result illustrates how complex the chain of cause and effect can be in the Earth system. No one would ever have predicted from first principles that increasing CFCs would have the effect of decreasing uptake of ocean carbon dioxide," says Andrew Watson, from the University of East Anglia, UK.

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No one knows the identity of Conficker's "patient zero" computer, or precisely when it was infected. It was probably a machine that the hackers already controlled. Once installed, the software set to work, surreptitiously scanning the internet for other vulnerable machines to send itself to.

The new worm soon ran into a listening device, a "network telescope", housed by the San Diego Supercomputing Center at the University of California. The telescope is a collection of millions of dummy internet addresses, all of which route to a single computer. It is a useful monitor of the online underground: because there is no reason for legitimate users to reach out to these addresses, mostly only suspicious software is likely to get in touch.

The telescope's logs show the worm spreading in a flash flood. For most of 20 November, about 3000 infected computers attempted to infiltrate the telescope's vulnerable ports every hour - only slightly above the background noise generated by older malicious code still at large. At 6 pm, the number began to rise. By 9 am the following day, it was 115,000 an hour. Conficker was already out of control.

That same day, the worm also appeared in "honeypots" - collections of computers connected to the internet and deliberately unprotected to attract criminal software for analysis. It was soon clear that this was an extremely sophisticated worm. After installing itself, for example, it placed its own patch over the vulnerable port so that other malicious code could not use it to sneak in. As Brandon Enright, a network security analyst at the University of California, San Diego, puts it, smart burglars close the window they enter by.

Conficker also had an ingenious way of communicating with its creators. Every day, the worm came up with 250 meaningless strings of letters and attached a top-level domain name - a .com, .net, .org, .info or .biz - to the end of each to create a series of internet addresses, or URLs. Then the worm contacted these URLs. The worm's creators knew what each day's URLs would be, so they could register any one of them as a website at any time and leave new instructions for the worm there.

It was a smart trick. The worm hunters would only ever spot the illicit address when the infected computers were making contact and the update was being downloaded - too late to do anything. For the next day's set of instructions, the creators would have a different list of 250 to work with. The security community had no way of keeping up.

No way, that is, until Phil Porras got involved. He and his computer security team at SRI International in Menlo Park, California, began to tease apart the Conficker code. It was slow going: the worm was hidden within two shells of encryption that defeated the tools that Porras usually applied. By about a week before Christmas, however, his team and others - including the Russian security firm Kaspersky Labs, based in Moscow - had exposed the worm's inner workings, and had found a list of all the URLs it would contact.

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POSSIBLY the clearest skies on Earth have been found - but to exploit them, astronomers will have to set up a telescope in one of the planet's harshest climates.

Michael Ashley of the University of New South Wales in Sydney, Australia, and his colleagues wanted to find the best sites for astronomy on the Antarctic plateau. Combining observations from satellites and ground stations with climate models, they evaluated different factors that affect telescope vision, such as the amount of water vapour, wind speeds and atmospheric turbulence.

The team found that the plateau offers world-beating atmospheric conditions - as long as telescopes are raised above its frozen surface. The ice makes the lowest layers of air on the plateau much colder than those above, forming an "inversion layer" that, together with the strong local winds, can lead to severe turbulence. This would blur a telescope's images.

The team's analysis showed the inversion layer is only about 20 metres thick, however. If a telescope was mounted above it, its view would be affected by far less turbulence than at other world-class observatory sites, says Ashley. "It's drier than Mauna Kea [in Hawaii] by a long way and drier than the Atacama desert [in Chile]," he says.

Such conditions would be good for studying star birth. Normally, water vapour in the atmosphere blocks telltale emissions from molecular clouds in star-forming regions of the Milky Way. But the air above the high area known as Dome A is so dry that a ground-based telescope there could observe stellar nurseries - something that's impossible anywhere else on Earth.

So far as Ashley's team know, Dome A seems the best site for astronomy (see map). China has already built a summer station there, with a small robotic observatory. Next best is Dome F, the site of a Japanese station.

But conditions may prove much better about 150 kilometres south-west of Dome A, at Ridge A (www.arxiv.org/abs/0905.4156). "We won't know until we make measurements there," says Ashley.

Life on the plateau isn't easy for telescopes, though. One problem is that ice can form on lenses and mirrors. Marc Sarazin of the European Southern Observatory's offices in Munich, Germany, says the harsh conditions demand the kind of approach used for space missions: "They will be single-purpose, short-lifetime instruments answering a precise scientific question," he says. General-purpose telescopes are best built in temperate latitudes like Chile's, he adds.

Ashley thinks the biggest difficulty lies elsewhere. "The main problems in Antarctica aren't so much the engineering," he says. "It's more convincing people that it is not as scary as it sounds."

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Hospitals in Greece have identified H1N1 swine flu in two students who had no contact with known cases of the virus and had not been in countries with widespread infection. The infections were discovered even though the students should not have been tested for swine flu under European rules. The Greek authorities say this shows the rules must change.

Indeed, an investigation by New Scientist earlier this month showed that the EU rules would exclude exactly such cases and could make H1N1 appear much less widespread in Europe than it is.

Takis Panagiotopoulos of the Hellenic Centre for Disease Control and Prevention in Athens and colleagues reported on 28 May in Eurosurveillance, a weekly bulletin published by the European Centre for Disease Prevention and Control (ECDC) in Stockholm, Sweden, that two Greek men returning home from Scotland had tested positive this week for H1N1 swine flu.

The two go to university in Edinburgh and had attended term-end parties at the end of last week. Both developed coughs and fevers at the weekend before flying back to Greece, where one went to hospital in Athens on Tuesday.

"The examining physician decided to take a pharyngeal swab, which was tested at the National Influenza Reference Laboratory for Southern Greece, although the patient did not meet the European Union and national criteria for the new influenza A (H1N1) testing," the team reports.

The swab was tested with a kit for H1N1 distributed by the US Centers for Disease Control and Prevention (CDC), and was positive for swine flu. The student in Athens warned the second student, who was now in Thesaloniki. He also tested positive. Both cases were mild.

Contacts of the two in Greece and Scotland and on the flights are being traced.

The Greek cases are "community acquired", meaning they have no contacts with known cases or countries with swine flu. The ECDC guidelines adopted by most EU countries, including Greece, recommend testing for H1N1 only when people have such contacts, excluding community acquired cases.

"It is of concern that with the present EU [testing criteria] we are by definition going to miss cases infected locally in the event of established community transmission," the Greek team warns. "It is probably necessary to modify the present EU definition … to also include clusters of patients with influenza-like illness, irrespective of travel history," they say, especially as the tourist season is getting under way.

Officially, swine flu has increased very slowly in Britain, even though the virus appears to be as contagious as ordinary flu. John Oxford of the University of London says the UK may have tens of thousands of mild, untested cases. The US CDC says there could be 100,000 cases in the US, even though only a few thousand, mostly severe, cases have been tested.

Finding community acquired cases outside the Americas is a requirement for declaring H1N1 swine flu an official pandemic, which the WHO has not yet done.

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Pinned prominently on Orion's shoulder, the bright red star Betelgeuse hardly seems like a wallflower. But a new study suggests the giant star has been shrinking for more than a decade.

Betelgeuse is nearing the end of its life as a red supergiant. The bright, bloated star is 15 to 20 times more massive than the sun. If it were placed at the centre of the solar system, the star would extend out to the orbit of Jupiter.

But the star's reach seems to be waning. New observations indicate the giant star has shrunk by more than 15 per cent since 1993. This could be a sign of a long-term oscillation in its size or the star's first death knells. Or it may just be an artefact of the star's bumpy surface, which may appear to change in size as the star rotates.

Betelgeuse is enshrouded by vast clouds of gas and dust, so measuring its size is difficult. To cut through this cocoon, Charles Townes of the University of California, Berkeley, and colleagues used a set of telescopes that are sensitive to a particular wavelength of the star's infrared light.

The team used these instruments to measure the size of Betelgeuse's disc on the sky. Over a span of 15 years, the star's diameter seems to have declined from 11.2 to 9.6 AU (1 AU, or astronomical unit, is the distance from the Earth to the sun).

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