September 2, 2011 10:46 pm

Where do clouds come from?

An experiment disproves the assumption that just sulphuric acid, ammonia and water can account for nucleation

The formation of clouds is the greatest of all the uncertainties in the scientific debate over climate change. Cloudiness cools the Earth by reflecting solar radiation back into space but the factors – natural and manmade – that encourage water droplets to condense remain largely unknown.

Particularly puzzling is the role of “atmospheric aerosols”, tiny liquid or solid particles that provide a nucleus around which droplets can form when the air is saturated with moisture. Without this seeding, water remains an invisible vapour in the air. Now, an experiment at Cern, the European particle physics centre near Geneva, is starting to shed light on the mystery.

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The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment studies the complex factors responsible for cloud formation in a large ultra-clean chamber. Under highly controlled conditions scientists introduce the gases believed to generate aerosol particles, together with ultraviolet radiation to simulate sunlight and high-energy particles from an accelerator, which simulate the cosmic radiation believed to play a role in cloud formation. Initial results, published in the journal Nature, include two significant findings.

One is that cosmic rays – high-energy particles reaching Earth from outer space – can indeed increase aerosol formation under some conditions, by ionising the gases in the atmosphere. This will please those who hold the controversial view that variations in cosmic radiation, related to cycles of solar activity, are an important driver of climate change.

Waste not

Lemurs play a vital role in maintaining the rainforests of Madagascar, by dispersing seeds through their droppings, researchers at the University of Roehampton have shown.

But Jasper Kirkby, head of the experiment, warns: “It is very premature to conclude that variation in cosmic rays is responsible for climate change.” He points out that the aerosols generated by simulated cosmic rays in CLOUD have been far too small to seed real clouds in the lower atmosphere.

The second and potentially more interesting result disproves the assumption in current climate models that just three gases – sulphuric acid, ammonia and water – can account for cloud nucleation.

“It was a big surprise to find that aerosol formation in the lower atmosphere isn’t due to sulphuric acid, water and ammonia alone,” says Kirkby. “Now it’s important to discover which additional vapours are involved, whether they are natural or of human origin, and how they influence clouds. This will be our next job.”

Although the precise identity of these “additional vapours” is still a mystery, Kirkby says that, by the process of elimination, they must be volatile organic (carbon) compounds. One example would be the terpenes given off by pine forests, which are responsible for natural haze.

Portions of snus©AFP

Portions of snus

The tobacco that can help smokers give up

Sweden is campaigning for the European Union to lift its ban on snus, the country’s popular smokeless mouth tobacco. Snus, which comes in little sachets that users tuck behind their upper lip, is banned outside Sweden on health grounds. But its supporters maintain that snus can help smokers give up cigarettes, which are far more harmful; they attribute the low rates of tobacco-related disease among Swedish men to their use of snus rather than cigarettes.

Now, in an attempt to inject some evidence into the debate, Swedish Match, the largest snus manufacturer, has sponsored a clinical study to show that the product can indeed help people smoke less. It was carried out in Serbia, where there is no tradition of oral smokeless tobacco.

The randomised, placebo-controlled, double-blind trial involved the researchers using a placebo pouch, based on a mixture of cocoa bean and oat seed fibres, which looked and tasted like snus but contained no tobacco or nicotine. The 319 participating smokers were divided at random into snus and placebo groups (it wasn’t divulged who was in which group).

The results, published in Harm Reduction Journal, show that the snus takers were more successful at stopping smoking – or drastically cutting their cigarette consumption – than the placebo group.

Although the trial was not large enough to give statistically powerful results, its organiser, Lars Erik Rutqvist of Swedish Match, says more data will be published shortly from a similar study in the US and combined with the Serbian data through the technique of meta-analysis.

The aim, he says, is to show that modern research methodology could produce objective evidence about the health benefits of snus. Whether Sweden’s EU partners can be convinced remains to be seen.

An Iberian lynx

An Iberian lynx

Lynx disproves need for genetic diversity

One of the biggest worries for animal conservationists, when a remnant population becomes very small, is its lack of genetic diversity, which can cause inbreeding and reduced ability to adapt to environmental change. But this may not always be a problem, according to a surprising genetic study of the Iberian lynx, Europe’s most endangered carnivore.

An international research team analysed ancient DNA from fossilised teeth and bones of Iberian lynx as far back as 50,000 years. They found remarkably little genetic variation throughout the period, suggesting that the cats survived in small numbers for tens of millennia with a level of DNA diversity that might previously have been regarded as unsustainably low.

“To see so little genetic diversity over such a long period of time indicates that population sizes were moderate,” says University College London’s Mark Thomas, a co-author of the study published in the journal Molecular Ecology. “But if small populations can exist for so long and with so little genetic diversity then this must say something about the survivability of similar endangered species today.”

The Iberian lynx was once found across Spain and Portugal. It is now restricted to two isolated groups, numbering around 250 animals in total, in southern Spain.

“These results show that low genetic diversity in the Iberian lynx is not in itself an indication of a population in crisis,” says Love Dalén from the Swedish Museum of Natural History.

Vibrio cholerae

Researchers have traced the origins of the current world cholera pandemic back to the 1950s

Cholera outbreak traced back to 1950s

The current global pandemic of cholera – the seventh to have swept the world over the past two centuries – originated in the Bay of Bengal in the 1950s and acquired antibiotic resistance 30 years later, according to a powerful piece of genomic detective work published in the journal Nature.

An international team, led by the Wellcome Trust Sanger Institute near Cambridge, analysed the genomes of cholera samples taken from 154 patients across the world during the past 40 years. By tracking changes in the DNA of the Vibrio cholerae bacteria, the researchers mapped the pandemic back to its roots in the Indian subcontinent and discovered the overlapping waves of transmission from there across the globe.

The El Tor strain, as it is called, started moving away from the Bay of Bengal in the 1960s. A key development came in 1982 when it gained antibiotic resistance by acquiring a new genetic region, SXT.

“Looking at the past 40 years of transmissions from continent to continent, we found that the Bay of Bengal acts as a reservoir for cholera, where it can thrive and spread,” explains Nicholas Thomson from the Sanger Institute. “By tracking how the disease is spread, our maps of transmission could influence future decisions on how to tackle this disease.”

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