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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Sadiq Khan gives Jeremy Corbyn's supporters a lesson on power

The London mayor doused the Labour conference with cold electoral truths. 

There was just one message that Sadiq Khan wanted Labour to take from his conference speech: we need to be “in power”. The party’s most senior elected politician hammered this theme as relentlessly as his “son of a bus driver” line. His obsessive emphasis on “power” (used 38 times) showed how far he fears his party is from office and how misguided he believes Jeremy Corbyn’s supporters are.

Khan arrived on stage to a presidential-style video lauding his mayoral victory (a privilege normally reserved for the leader). But rather than delivering a self-congratulatory speech, he doused the conference with cold electoral truths. With the biggest personal mandate of any British politician in history, he was uniquely placed to do so.

“Labour is not in power in the place that we can have the biggest impact on our country: in parliament,” he lamented. It was a stern rebuke to those who regard the street, rather than the ballot box, as the principal vehicle of change.

Corbyn was mentioned just once, as Khan, who endorsed Owen Smith, acknowledged that “the leadership of our party has now been decided” (“I congratulate Jeremy on his clear victory”). But he was a ghostly presence for the rest of the speech, with Khan declaring “Labour out of power will never ever be good enough”. Though Corbyn joined the standing ovation at the end, he sat motionless during several of the applause lines.

If Khan’s “power” message was the stick, his policy programme was the carrot. Only in office, he said, could Labour tackle the housing crisis, air pollution, gender inequality and hate crime. He spoke hopefully of "winning the mayoral elections next year in Liverpool, Manchester and Birmingham", providing further models of campaigning success. 

Khan peroration was his most daring passage: “It’s time to put Labour back in power. It's time for a Labour government. A Labour Prime Minister in Downing Street. A Labour Cabinet. Labour values put into action.” The mayor has already stated that he does not believe Corbyn can fulfil this duty. The question left hanging was whether it would fall to Khan himself to answer the call. If, as he fears, Labour drifts ever further from power, his lustre will only grow.

George Eaton is political editor of the New Statesman.