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Cloud feedback could accelerate global warming

Low-level clouds are involved in a positive feedback mechanism that could exacerbate global warming — according to a study of cloud and temperature records from the north-eastern Pacific Ocean. Scientists in the US have found that low-level cloud cover decreases when the sea surface gets warmer. Fewer clouds mean that more sunlight reaches Earth’s surface, leading to further warming.

Understanding how climate change is affected by low-level clouds is one of the key challenges facing climate scientists. Such clouds are known to have a net cooling effect — so if rising temperatures lead to more low-level clouds, this negative feedback mechanism could mitigate global warming. But if higher temperatures lead to fewer clouds, the feedback is positive and global warming could be enhanced.

Observational data linking low-level cloud cover and temperature are scarce and the formation and dissipation of clouds is notoriously difficult to model and integrate into global climate simulations.

Now, Amy Clement and Robert Burgman of the University of Miami and Joel Norris of the University of California-San Diego have done a statistical analysis of 55 years of cloud cover and temperature observations for the north-eastern Pacific Ocean. Their study provides the best evidence yet that low-level cloud cover decreases as temperature increases — that the feedback mechanism is positive.

Wrong type of clouds

When temperatures are higher, Clement believes that water rises higher into the atmosphere to create upper-level clouds at the expense of low-level clouds. These higher clouds, however, have a net greenhouse effect and therefore their creation could further boost the positive feedback.

The team compared their findings with feedback predictions made by 18 leading climate models. Only two models predicted a positive feedback and one of these — HadGEM1 from the UK’s Hadley Centre — was particularly good at reproducing the observed relationships between cloud cover, atmospheric circulation and temperature.

Clement believes HadGEM1 performed well because Hadley scientists have “spent a lot of time looking at the lower kilometre of the atmosphere”.

Clement told physicsworld.com that the strength of the positive feedback is in the upper range of that predicted by the Intergovernmental Panel on Climate Change (IPCC). An important consequence of this is that global warming could be worse than many scientists had anticipated. Indeed, HadGEM1 predicts a 4.4° average global temperature increase when carbon dioxide is doubled — compared to the 3.1° median of the 18 models.

A perfect ‘laboratory’

The team focused on the north-eastern Pacific Ocean because the average temperature in the region fluctuates significantly on a ten-year timescale — and because comprehensive cloud-cover observations have been made over the years by satellites as well as by the many ships that sail through the region. This makes it a perfect “laboratory” for studying the relationship between clouds and temperature.

Clement says that it is possible that the observed feedback is specific to the north-eastern Pacific and may be different in other parts of the world where there is significant low-level cloud cover. To test this, the team is now doing a similar study of data from the south-eastern Pacific.

Matthew Collins of the Hadley Centre said that the result sheds significant light on the role of clouds and will be used to evaluate and improve the performance of climate models. However, he cautions that cloud feedback is only part of the picture — and the type of clouds studied by Clement and colleagues are significant only in certain parts of the globe.

This research appears in the latest edition of Science.

Moonrockin' the Science Museum

Universal hit: Apollo astronauts took country music into space Credit: Nasa

By James Dacey

Question: What do David Bowie, U2, Coldplay and London’s Science Museum have in common?

Answer: They’ve all been given the “Eno treatment”.

Since quitting the art-rock group Roxy Music in the early 1970s the English musician / musical theorist / political commentator has become one of the most revered names in pop music, collaborating with some of the biggest names in the business. Brian Peter George St. John le Baptiste de la Salle Eno — as his extended name goes — is well-known for consistently pushing the boundaries of music. Many of his albums are fused with the concepts and ideals of minimalist art and his name has become a by-word for pretty much any interesting electronic music.

In 1980 Eno worked with his brother Roger and Canadian guitarist Daniel Lanois to create the ambient album Apollo. Inspired by hearing that some of the astronauts on the Apollo missions had taken recordings of country music with them into space, Eno set out to record a concept album of “zero-gravity country music”. My own ears have never been treated to this ambient delight but my muso colleague describes it as “alien noise that perfectly captures the spirit of the Apollo missions”.

Now, to celebrate the 40th anniversary of the Apollo 11 Moon landing, Eno has collaborated with South Korean composer Jun Lee to perform a special arrangement of the album at the London Science Museum. The shows took place on Monday and Tuesday and the music was accompanied by original footage of the Moon landings assembled by director Al Reinert projected onto the giant screen of the Science Museum IMAX cinema.

It’s not yet clear if Eno will be repeating this show in any other venues but I will keep my ears to the ground for any ambient murmurings and let you know…

Newfound order in the valleys

If you have ever gazed out of the window when flying over particularly barren landscapes you will have noticed that ridges and valleys seem to crop up at remarkably uniform spacing. This feature of the Earth’s surface has long since been recognized by geographers but they have always struggled to identify the underlying physical factors that control the distribution of these landforms. Now, however, a team of researchers in the US and Switzerland have developed the first general theory to describe and predict the mechanics of this natural phenomenon.

Taylor Perron at Massachusetts Institute of Technology (MIT) and his colleagues argue that ridge spacing represents a fundamental balance in nature between the slow “creep” of soil and the branching of water channels over the Earth’s surface. To verify their theory, the MIT scientists compared figures from their numerical model with high resolution images taken of the Earth from above. The researchers believe that a quantitative understanding of valley evolution could also yield valuable information about the nature of localized climates throughout Earth history.

Historical landscapes

Some of the early work on landscape morphology from the late 19th century was already focusing on the segmentation of landscapes into ridges and valleys. But until recently, most studies have remained qualitative, largely because we have lacked the topographic maps with sufficient resolution. Another barrier to developing numerical models is that erosion acts very slowly — just a tenth of a millimetre per year on average — and often in fits and starts, so it’s almost impossible to measure directly.

Perron and his team have overcome the mapping problem by using a relatively new technology called LiDAR, which combines GPS with aircraft-mounted lasers. This has been used to produce digital topographic maps covering large areas with resolutions of 1 m per pixel. Another useful feature of LiDAR is it can filter out the laser signals returned from vegetation, and keep only the ones that hit the exposed ground. “We can virtually deforest the landscape, and measure the ridge-valley wavelengths that were previously obscured by trees,” Perron told physicsworld.com.

The researchers have also managed get around the difficulty of measuring erosion rates in order to confirm the river incision and creep parameters in their equations. They achieved this by developing a new technique for calibrating those parameters using only the topography, so we were able to directly compare the wavelength that emerges in model landscapes observed in the field.

Shared geography

The researchers focused on regions that are soil-covered and “low relief”. These landscapes are relatively free of vegetation and the vertical height of the ridges and valleys is not too large relative to their horizontal dimensions. “Basically, this is a disclaimer that our model does not apply to landscapes that are so steep that landslides and debris flows occur frequently,” said Perron. The study was based on sites mostly in the western US but these landscapes are also common in many other regions of the world including the north-eastern US and the UK.

The purpose of collecting these images was to compare them with a numerical model put forward by the same researchers last year. To their delight the MIT scientists found strong agreement between the two sets of data and this led them to a non-dimensional quantity that gauges the balance between soil creep and channel incision — a trade-off that governs the size of ridge spacing. Their model also confirms the long-held rule of thumb that drier climates and weaker rocks are associated with closely spaced valleys in which river incision dominates over creep.

What’s more these findings could help earth scientists to develop historic climate records. “We evaluate how the time-averaged climate has varied among regions by comparing their wavelengths,” said Perron. “By comparing the topography with independent climate records, we can also start to approach the question of which aspects of a variable climate have the strongest effect on long-term erosion and sediment transport,” he added.

Kelin Whipple, an earth scientist at Arizona State University believes the impact of this research will be felt across a range of disciplines. “I think this study of ridge-valley spacing will drive further and deeper analysis of the relations among climate, climate change, and landform morphology in general.” However, he also cautions against viewing this as a key to understanding the full details of past climates. “It is certainly part of the puzzle in trying to determine how climate and climate history is reflected in the shape of landforms — there is promise here, but it’s a complex problem and not fully resolved.”

This research was published in the latest edition of Nature.

How a bat got its big nose

A typical horseshoe bat (left) and Bourett’s horshoe bat

By Hamish Johnston

Most biologists believe that the giraffe’s long neck evolved to allow the creature to munch on leaves not accessible to other grazing animals. But are such extreme biological features always “optimal adaptations” to specific environmental conditions? In other words, is the giraffe’s neck simply the best possible solution for reaching those tasty treetop morsels? Or did its design come about from a complicated array of evolutionary factors, some of which had nothing to do with finding dinner?

This is an important question for evolutionary biology because the study of extreme features that are true optimal adaptations could help scientists to better understand the forces that drive evolution.

Now a physicist, biologist and mechanical engineer have joined forces to show that the unusually long nose of the Bourett’s horshoe bat is the optimal size for focusing a beam of ultrasound — which the bat uses to navigate.

Native to the rain forests of south east Asia, the bat has a nose that’s about 9 mm long — which is about twice the length of a typical horseshoe bat.

The team used a computer model to calculate the acoustic properties of the “noseleaf” — a structure that protrudes from the bat’s nose and is made of made of folded skin called “sella”

You can read their paper in Physical Review Letters.

They looked at a number of different nose lengths and “By predicting the width of the ultrasonic beam for each of these nose lengths with a computational method, we found that the natural nose length has a special value”, explained team-leader Rolf Mueller of Virginia Tech. in the US.

“All shortened noses provided less focus of the ultrasonic beam, whereas artificially elongated noses provided only negligible additional benefits. Hence, this unusual case of a biological shape can be predicted accurately from its physical function alone.”

So that’s how Bourett’s horshoe bat got its big nose.

Film review: Hawaiian Starlight

The CFHT dome at night. Credit: Jean-Charles Cuillandre

By Margaret Harris

We’ve received several more physics-related films in the months since the film review series that appeared on physicsworld.com earlier this year, so we’ve decided to run a new batch of reviews over the next couple of weeks. First up: Hawaiian Starlight by Jean-Charles Cuillandre.

With its sweeping panoramas of galaxies, nebula and the cluster of telescopes perched atop Hawaii’s Mauna Kea volcano, Hawaiian Starlight is the ultimate astronomy screen-saver. At least, that’s how it comes across if you watch it on a computer screen in a brightly-lit office. On a big screen in a dark room — perhaps with a drink, and the right group of friends — I suspect it would be a near-spiritual experience. Throughout the film’s 43-minute running time, images of interstellar objects alternate with time-lapse footage of the telescopes that took them. And that’s it. There is no voice-over, no gesturing science “personality” to ram home the significance of what you’re watching, nor even much text. It is just you, the stars, the scopes, and a curiously hypnotic soundtrack borrowed from the Halo video game series. It’s marvellous.

Part of the marvel is the sheer dedication of filmmaker Jean-Charles Cuillandre, an astronomer at the Canada-France-Hawaii Telescope who spent seven years collecting footage of telescopes and the Mauna Kea landscape. The resulting time-lapse movies make up the bulk of the film, and range from simply beautiful to delightfully whimsical. At 1000 times normal speed, a telescope dome opening and closing bears a striking resemblance to Pac-Man, and “cute” is really the only word for a sequence in which three sub-millimetre telescopes twitch in time with the music.

But for the most part, this film inspires wonder rather than giggles. We all know the official reasons for placing telescopes on remote mountaintops: clear skies, thin atmosphere, and low light pollution make for better images. Watching Hawaiian Starlight, however, one wonders whether more subtle factors could play a role: the awesome environment of Mauna Kea’s summit must surely encourage its scientific visitors to think deeply about the universe.

Asking the big questions in London

Trivial matters: Subir Sarkar sets up for his dark energy demolition job

By James Dacey

People often ask me – usually in bewildered tones – what is was that could possibly have appealed to me about physics, let alone convinced me it was a good idea to go study this baffling subject at university.

So it goes… I normally find myself agreeing with them that school physics could be intensely dull, inaccessible, and completely disconnected from everyday life. “But“, I tell them, it was the big ideas that got me in the end – the sense that I was grappling with some of the most profound questions we could ever ask. More recently, I have developed an interest in some of the more “mundane” areas of the subject – particularly the pursuit of sustainable energy innovations – but it is still the bigger picture stuff that really feeds my passion.

I was reminded of all this last night when I popped along to Imperial College in the heart of London town to attend a public debate on “The Fate of the Universe”. The two speakers tackling this small topic were Imperial’s own Andrew Jaffe – an astrophysicist who you may know through his blog Leaves on the Line and Subir Sarkar – a theoretical physicist from the Rudolf Peierls Centre at Oxford.

Jaffe was up first and he introduced the idea of dark energy. He is a firm believer in the stuff and pitched the model as a means of explaining why the rate of expansion of the universe is speeding up when really it should be slowing down under the attractive force of gravity. The American physicist argued that, whilst not perfect, dark energy is the best model we have to fit the data.

(more…)

Cold war tourism hotspot

By Hamish Johnston

Is it cold and rainy where you are?

Then why not pack your bags for Hanford, Washington, where the forecast calls for blazing sunshine and temperatures in the mid-30s (90s in old money) for the rest of the week.

While in town you could take a guided tour of the famous “B Reactor” at Hanford, where much of the plutonium for the Manhattan project was made. Some of this material ended up in the “Fat Boy” bomb that detonated over Nagasaki.

After fuelling many a cold-war weapon, Hanford B was shut-down in 1968 — but instead of being “entombed” like its neighbours, the reactor was designated a National Historic Landmark last year.

The plan is to turn the reactor into a museum and the Department of Energy is gearing up by offering occasional guided tours of the site — and the BBC’s Rajesh Mirchandani boarded the tour bus for what was a front line in the Cold War. You can watch his report here.

But don’t bring the kids — tourists must be at least 18 — and wear sensible shoes.

Hanford guide Michelle Gerber

Remaining tours for this year are on July 25, August 8, 15, 22, and 29
and September 5, 12, 19, and 26. Hanford’s online booking system says the tours are fully booked, but suggests you check back occasionally in case anyone has dropped out.

And if Hanford B is like most defunct reactors worldwide, it will be there for a very, very long time — so you’ll get your chance to see it eventually!

Controversy bubbles over particle physics prize

The European Physical Society (EPS) has defended its handling of its 2009 prize for high-energy and particle physics, despite complaints that the awarding committee has overlooked a vital scientific contribution to the prize-winning work. The biennial CHF5000 award, presented yesterday at a conference in Kraków, Poland, went to collaborators on the Gargamelle experiment at CERN for their 1973 discovery of the weak neutral current — one of the ways in which the weak nuclear force is mediated between fundamental particles. However, the award did not formally recognize the “leptonic” evidence for neutral currents, without which some particle physicists say the discovery could not have been made.

I am amazed and appalled that the leptonic neutral-current channel will not be recognized in the EPS prize Alan Michette, King’s College London

Several Gargamelle collaborators have contacted the EPS with their objections, with Alan Michette of King’s College London and Don Perkins of Oxford University requesting that their names be removed from the prize list. “I am amazed and appalled that the leptonic neutral-current channel will not be recognized in the EPS prize,” Michette told physicsworld.com. “In my opinion this is a historical and scientific error that is being committed in the face of all expert advice to the contrary.”

Smoking gun of unification

Alan Michette

The discovery of weak neutral currents put the nascent standard model of particle physics — namely electroweak theory — on solid experimental ground. Until then, all known weak processes involved a rearrangement of electric charge (so called charged-current reactions) and historically could be described as taking place at a single point. But by the early 1970s a better theory of the weak force had emerged in which charged-current interactions are mediated by a charged particle called the W boson and a new interaction, mediated by a neutral particle called the Z boson, was predicted. The theory required that the Z particle would “mix” with the photon (the mediator of electromagnetism) such that the weak and electromagnetic forces were unified in a single theory.

The Gargamelle results allowed physicists to estimate the ratio of the masses of the W and Z particles, which were directly observed at CERN in the early 1980s and then studied in detail with the lab’s Large Electron Positron collider. That machine has since made way for the Large Hadron Collider, which should unearth the mechanism (widely expected to involve the Higgs boson) responsible for breaking the electroweak force into the two entities we perceive in the low-energy universe today.

Gargamelle, which was a bubble chamber that now stands outside on display near CERN’s main restaurant, recorded the first neutral-current event in December 1972. Filled with 12,000 litres of dense liquid in which charged particles leave trains of tiny bubbles, an electron (a type of particle called a lepton) appeared to have been kicked by an incoming neutrino, which leaves no bubble trace. Soon afterwards, the Gargamelle team had observed many more neutral-current events, this time when an incoming neutrino struck a proton (a type of particle called a hadron).

Vital confirmation

While there were many more “hadronic” events than there were “leptonic” ones, it was harder to pick them out from the bulk of background events that produced a similar signature, and it took a year for the Gargamelle results to be fully accepted. (In fact, an experiment at Fermilab in the US turned out to have already seen hadronic neutral-current events yet had put them down to neutrons). Since the electroweak theory made firmer predictions for the leptonic channel than it did the hadronic channel, largely because protons are not elementary particles, Gargamelle physicists say that the single-electron event was vital in confirming the neutral-current prediction.

Gerard ‘t Hooft of the University of Utrecht, who shared the 1999 Nobel physics prize for his theoretical work on electroweak interactions, says both the leptonic and hadronic contributions were important in the discovery of neutral currents, but that they were also rather different discoveries. “Now, of course, it’s obvious that there is a single weak interaction, but in those early days it was far from clear,” he said. “Having neutral currents among leptons doesn’t necessarily mean there are neutral currents among hadrons, and vice versa.”

Decision stands

James Pinfold

The two Gargamelle results were published in September 1973: one paper reporting the leptonic event and the other the hadronic analysis. The controversy over this year’s EPS prize stems from the decision to award it only to authors of the hadronic paper, leaving four authors of the leptonic paper — Charles Baltay of Yale University, Michel Jaffre of IN2P3-CNRS in Orsay, Jacques Lemonne of Vrije Universiteit in Brussels and James Pinfold of the University of Alberta — out in the cold.

The leptonic channel was at least as important as the hadronic channel in confirming the discovery of neutral currents with Gargamelle James Pinfold, University of Alberta

“The leptonic channel was at least as important as the hadronic channel in confirming the discovery of neutral currents with Gargamelle,” says Pinfold, who wrote to the chair of the EPS High Energy and Particle Physics Division Board, Per Osland, on behalf of all four affected authors requesting that the board amend the prize accordingly. “My request was rebuffed,” he says.

In defence of its decision, the EPS cites the titles of the two neutral-current papers. “The Gargamelle collaboration did a variety of measurements and published many papers with a variety of authors,” Osland said. “The board decided to give the prize for the ‘observation of the weak neutral current interaction’, so it was then natural to point to the ‘Observation…’ paper, where observation was actually claimed, rather than the ‘Search for…’ paper, which presented the leptonic event but did not claim observation of the neutral current.” Osland added that the EPS can not remove names from the list of winners because that would amount to tampering with the list of authors of a paper published 36 years ago.

Michette, however, puts events down to bureaucratic intransigence. “The EPS decided to ignore the voices of a number of members of the Gargamelle Collaboration,” he said. “Simply put, the committee couldn’t admit that it had made a big mistake.”

Listen to Heisenberg compare Sommerfeld, Born and Bohr

Martin Schwarzschild being interviewed in 1977

By Hamish Johnston

If you’d like to listen to Werner Heisenberg compare the physics prowess of Arnold Sommerfeld, Max Born, and Niels Bohr , just click here and you will be taken to the new online Oral Histories section at the Niels Bohr Library & Archives.

The American Institute of Physics — which runs the library — has unveiled a vast online archive of interviews with some of the 20th century’s most prominent physicists.

The archive includes pioneers of quantum theory such as Heisenberg and Max Born, Paul Dirac, Niels Bohr and Eugene Wigner.

The list of histories reads like a Who’s Who of physics. The earliest interviews were done in the 60s and the latest — including NASA’s James Hansen were done quite recently.

Most of the histories are available as written transcripts, but a few voice clips are also available — including Heisenberg, Hans Bethe, George Gamov and Steven Weinberg.

A word of warning about the site: I found that many of the links didn’t work — and I could not actually listen to Heisenberg and company (this could be a problem with my browser). But it’s worth persevering.

Is this the ‘Article of the Future’?

I can’t believe they used to print these things out!

By James Dacey

Do you relish the challenge of ploughing through online abstracts in search of the article’s “bottom line”?
Do you still print out all your papers before going at them with the fluorescent pen?
Do you still love the arcane language and the classic layout: intro – method – results – images – discussion?

Well, your habits could be about to change with the launch of a new initiative by a leading scientific publisher. The Article of the Future project by Elsevier has set out with a modest aim to “redefine how a scientific article is presented online”.

One of the key features of the new format is a kind of web-based filing system in which different aspects of the research – i.e. intro, images, discussion – can be “taken out” and viewed separately.

Intros are different – including a bulleted article highlights section and a graphical abstract. Multimedia is present throughout such as interviews with the authors. If interested, you can see a couple of prototypes of the new format here.

Elsevier say the project is intended to promote interdisciplinary scholarship and help readers identify more quickly which papers are most relevant to their interests.

So how will this new format go down in the physics community?

I reckon pretty well, though I’m sure some purists – especially the theoreticians – will argue that you can’t always reduce the subtlety of their arguments to a few bullet points.

What’s more, if this does catch on with other publishers, it will be interesting to see how the bloggers respond. Because it seems to me that a large aspect of their job at present is to trawl through the piles of paper and pick out the highlights from their field. But if the journal publishers have already done this… what then?

One outcome is that they become more critical. The bloggers will – once and for all – move away from just cheerleading for their chosen specialism. We might see a new form of blogging in which the key players start championing / laying into research with a new-found vigour.

Well, whatever happens I reckon this is another key development in an interesting transitionary period for both the publishing and media sectors.

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