A team of scientists led by a British academic has solved a long-standing enigma to explain how up to half the clouds in the sky are formed. And in finally cracking the problem of how planet-cooling clouds are conjured from what might seem to be thin air, the researchers found that humans play a significant role. It is a discovery that could fundamentally change our understanding of climate change, and may even mean experts have underestimated just how warm the planet will get over the next century.
The mystery was that many clouds appeared in the sky even though there were no "seeds" – often just specks of dust – that must be present for water droplets to form in the air. But, writing in the journal Nature last week, researchers from the Cern laboratory in Switzerland described for the first time how a chemical soup of gas vapours can react to form the necessary tiny particles.
To do so they had to build a chamber of "unprecedented cleanliness" at Cern in order to ensure they could work out exactly what was going on in the atmosphere.
"This is the first time that atmospheric particle formation has been reproduced with complete knowledge of the participating molecules," said Professor Jasper Kirkby, leader of the research team. "This is an important step forward, but we still have a long way to go before we fully understand the processes of aerosol formation and their effects on clouds and climate."
The research showed that gases called amines – produced in large quantities as a result of farming cattle and other animals – can help form the seed particles when combined with sulphuric acid in the air. Breathe in air from a farm and it is likely you are getting a lungful of amines, as they come from the breakdown of proteins and can be found in animal slurry. Rotting fish gives off a particularly concentrated dose.
Professor Kirkby, originally from Manchester, stressed it was possible that clouds could be produced in a similar way with sulphuric acid but with different kinds of vapours than amines. He said this newly discovered process would have to be factored into climate change models used by the Intergovernmental Panel on Climate Change (IPCC).
The lack of knowledge about aerosols – particles suspended in the atmosphere – and their effect on clouds is widely recognised as the major source of uncertainty in predictions about global warming. "We have to understand how clouds have been changed by human activity or natural activity if we are to understand climate change in the 20th century and therefore have reliable projections in the 21st century," Professor Kirkby said.
The global average temperature on land and sea rose by 0.85C from 1880 to 2012, the IPCC said in a major report last month. The fact that amines are produced by animal husbandry means that humans are responsible for a previously unknown cooling effect on the planet. So the overall man-made "forcing" of the climate – once greenhouse gases are taken into account – may actually be less than thought.
And that could be bad news because, Professor Kirkby said, it suggested "the climate may be more sensitive than previously thought". "If there's been more cooling from aerosols than thought at the moment then this temperature rise will have resulted from a smaller forcing – or change – than previously thought," he said. "That would mean the projected temperatures this century for a doubling of carbon dioxide may be bigger than current estimates."
In its report the IPCC said that temperatures could increase by between 0.6C and 4C by 2100 depending on carbon emissions. The latter figure would cause sea levels to rise substantially and increase the frequency of storms, droughts and other hazardous weather. A temperature rise of more than 2C above pre-industrial levels is seen as the point at which the effects become dangerous.
The study suggests a possible way scientists could create clouds to help cool the Earth, although such geo-engineering is controversial. Amines are also used in carbon-capture at power stations and factories, so this might be a spin-off benefit.
Gerald North, professor of atmospheric sciences and oceanography at Texas A&M University in the US, welcomed the research, saying that aerosols had been "really very poorly understood". He described the idea that climate models may have been underestimating global warming over the next century as "very interesting", but also warned of the need for more research on the subject.
Professor North suggested the discovery might offer some form of hope for the planet. "We don't know if these amines are increasing the same way that carbon dioxide is increasing," he said.
"If they were increasing at the same rate, maybe everything would be fine! But we don't know."
Piers Forster, professor of physical climate change at Leeds University, said people had previously tried to work out the cloud-making process, speculating about ammonia, cosmic rays and other factors.
"If you get amines being produced in parts of the world that are very pristine, this could have a direct effect on clouds," he said. While the research would help improve climate models, he said he doubted it would alter temperature projections significantly.