We can thank our clouds for saving us from a fate worse than Venus's

Clouds are essential as they reflect and scatter sunlight back into space - but nobody knows how hot the planet can become before the clouds no longer help us.

No one wants to think about cloudy skies in August but if they’re up there, be grateful. According to research published in Nature Geoscience on 28 July, we can thank clouds for saving us from a fate worse than Venus’s.

Venus – a barren, hot planet – suffered from the “runaway greenhouse effect” when its temperature rose past a critical point. That, it seems, arose from having too much thermal insulation resulting from the heat-storing greenhouse gases in the planet’s atmosphere.

On Venus, as on earth, carbon dioxide was an important contributor. Our planet is wet and heating it creates a lot of water vapour, a far more potent insulator than carbon dioxide. The more water vapour there is, the faster warming occurs.

Once you hit the point of no return at which the runaway effect starts, it would take only a few thousand years for life on earth to become untenable.

The recently published calculations show that the Venus effect could happen here – if it weren’t for clouds. They look white and fluffy to us because they scatter light. The tops of the clouds do the same, scattering and reflecting sunlight back into space before it has the chance to warm the earth and take it into the runaway scenario.

There’s still some uncertainty in the calculations, however: we don’t know exactly how hot we can let the planet become before the clouds can no longer help us. Unfortunately, uncertainty in other areas is pushing us in the right direction to find out.

The Intergovernmental Panel on Climate Change (IPCC) will publish its fifth assessment report next year. A draft report of some of its data, leaked to the Economist, suggests that increasing carbon-dioxide levels won’t warm the atmosphere as much as we had previously thought. In 2007, the IPCC stated that concentrations of between 445 and 490 parts per million (ppm) of carbon dioxide were likely to result in a rise in temperature of 2° to 2.4° Celsius above the temperatures before the Industrial Age. The new data suggests that 425 to 485ppm would give a rise of 1.3° to 1.7° Celsius.

The Economist threw in plenty of caveats (“The two findings are not strictly comparable”; the data comes “from a draft version of the report, and could thus change”) but evidently felt the burden of reducing carbon emissions is not as onerous as it once seemed. “It is clear,” the paper declared, “that some IPCC scientists think the projected rise in CO2 levels might not have such a big warming effect as was once thought.”

As it turns out, it’s not just carbon dioxide that we need to worry about. US researchers have been mapping the gas leaks from pipelines in urban areas. Boston has more than 3,000 leaks in the pipelines that deliver gas to homes and industries. Preliminary data from Washington, DC indicates that the capital is just as prone to leaks. It’s of huge concern because methane is 25 times more potent as a greenhouse gas than carbon dioxide. If similar figures apply to every other major city with an ageing gas infrastructure, perhaps the chances of earth slipping into a runaway greenhouse effect need revising upwards.

We can be sure those figures won’t be in the IPCC report, however. As for the ones in the Economist, we’ll just have to wait and see. In many ways, it doesn’t matter: the numbers are out there now and will be put to work by those keen to make sure we don’t punish carbon emitters. Such a leak is not going to make governments feel inclined to do something about the problem – they can just keep their head in the clouds.

Sunset over Tiananmen Square after a day of heavy pollution in Beijing. Photograph: Getty Images.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 12 August 2013 issue of the New Statesman, What if JFK had lived?

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Theresa May raises UK terrorist threat level to "critical"

A further attack may be "imminent" and armed soldiers will be deployed on the streets. 

After last night's horrific attack in Manchester, Theresa May has announced that the terrorist threat level has been increased from "severe" to "critical" - meaning a further attack may be imminent. The Prime Minister, following the advice of the independent Joint Terrorism Analysis Centre, said in a statement from No.10 Downing Street: "The work undertaken throughout the day has revealed that it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack."

The new threat level, the highest available and last imposed in 2007, means that up to 5,000 soldiers will be deployed on the streets to replace armed police, guarding sensitive points such as parliament and railway stations. The intelligence services are likely to have been troubled by the relative sophistication of the Manchester Arens attack, a nail bomb, which murdered 22 people and injured 59 others.

May added: "This morning I said that the Joint Terrorism Analysis Centre, the independent organisation responsible for setting the threat level on the basis of the intelligence available, was keeping the threat level under constant review. It has now concluded, on the basis of today’s investigations, that the threat level should be increased for the time being from severe to critical. This means that their assessment is not only that an attack remains highly likely, but that a further attack may be imminent.”

Operation Temperer - allowing military personnel to take to the streets - had been enforced, May announced. “This means that armed police officers responsible for duties such as guarding key sites will be replaced by members of the armed forces, which will allow the police to significantly increase the number of armed officers on patrol in key locations. You might also see military personnel deployed at certain events such as concerts and sports matches, helping the police to keep the public safe.” 

The terrorist threat level was last raised to "critical" in June 2007 following the attempted bombing of a Tiger Tiger night club in London and the Glasgow airport attack. It was also increased after the failed 2006 Heathrow bomb plot. On both occasions, the "critical" status remained in place for less than a week. 

May will chair another meeting of the government's emergency Cobra committee at 9:30am tomorrow. The Conservatives and Labour have suspended all national and local election campaigning until further notice.

In her concluding remarks, the Prime Minister emphasised: "I do not want the public to feel unduly alarmed." She continued: "We have faced a serious terror threat in our country for many years and the operational response I have just outlined is a proportionate and sensible response to the threat that our security experts judge we face. I ask everybody to be vigilant and to co-operate with and support the police as they go about their important work.

"I want to end by repeating the important message I gave in my statement earlier today. We will take every measure available to us and provide every additional resource we can to the police and the security services as they work to protect the public.

"And while we mourn the victims of last night’s appalling attack, we stand defiant. The spirit of Manchester and the spirit of Britain is far mightier than the sick plots of depraved terrorists, that is why the terrorists will never win and we will prevail." 

George Eaton is political editor of the New Statesman.

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