The heat is on: how global warming could suddenly tip over and ignite calamity

Scientists at Nasa, instead of staring into the skies, have been using satellites to look down at the world and track how it is changing. Within a year, the US space agency disclosed this week, an area of sea ice “the size of Texas” had been lost from the Arctic.

Data pieced together by Nasa showed that Arctic perennial sea ice, which normally survives the summer melting season, abruptly shrank by 14 per cent between
2004 and 2005. The report found: “Perennial ice can be 10 or more feet thick. It was replaced by new, seasonal ice only one to seven feet thick that is more vulnerable to summer melt.”

The disappearance of Arctic ice, the retreat of glaciers from the Himalayas to Peru, earlier springs and hotter summers – all these effects have been recorded by climate scientists in recent years. They form the basis of Al Gore’s polemic on climate change, An Inconvenient Truth, in which the former US vice- president describes huge cliffs of ice breaking apart, glaciers dropping suddenly into the sea, and polar bears found drowned because they cannot swim between ice floes as they used to.

This, as everyone knows, is global warming. Even those sceptical about whether the warming is caused by fossil fuel combustion accept that world temperatures have risen and look set to continue upward. Mr Gore’s film, which has been showing in the US since May – grossing $23m (£12m, €18m) – and opens in the UK today, has raised American awareness about climate change in the face of the federal government’s stance against the Kyoto protocol, designed to curb it.

US state governments and businesses are beginning to take action of their own to avert global warming by reducing the greenhouse gas emissions under their control. These measures, repeated across the globe, may by some estimates allow the world to stabilise emissions by the middle of the century.

But will that be soon enough? A growing body of scientific opinion suggests the world may be about to experience not a gradual rise in temperatures over several decades but a wild careering into climate chaos.

That is because some of the changes triggered by warming temperatures create a “feedback” effect of their own. These feedbacks can cause the warming trend to accelerate further or bring serious disruption to regions of the world (see box).

In this view, the rising proportion of carbon dioxide in the atmosphere, by creating feedbacks, is pushing the earth’s climate through a series of thresholds or tipping points that threaten to bring cataclysmic consequences. Those could include a much more rapid melting of the Arctic ice and the Greenland ice sheet than previously predicted, the accelerated melting of permafrost, the cessation of the Indian monsoon, a rapid dying back of forest in the Amazon and a halting of the sea currents that help bring warm weather to Europe.

The most obvious of these magnifier effects is in the Arctic, where the world’s warming has been much more pronounced than the average across the globe. Why? Sea ice – because it is bright white – reflects back much of the sun’s rays, in effect cooling the planet, Mr Gore’s film explains. But melting ice leaves more of the darker sea exposed, which then absorbs more heat, which causes more ice to melt, thus exposing more sea – a spiral of warming that quickly takes on a momentum of its own.

The Nasa report appears to confirm this feedback loop.

There is more apparent confirmation in a study last month in Science, journal of the American Association for the Advancement of Science, that found the speed at which the Greenland ice sheet was melting had risen threefold in the past two years compared with the previous five.

Peter Smith, special professor in sustainable energy at Nottingham University, told the British Association science festival last week: “We could reach the tipping point within 15 to 20 years from now, which would give us just 10 years in which to determine the destiny of our planet.” Jay Gulledge, senior research fellow at the Pew Centre on Global Climate Change, says climatologists “have dramatically under-estimated how responsive the climate is to warming”.

The world’s current attempts to cut emissions, such as the Kyoto protocol and the Asia-Pacific Partnership on Clean Development and Climate, a collaboration between developed and developing countries, presume a slowdown over decades of the rate of increase in the world’s output of greenhouse gases. But Myles Allen of Oxford University, one of the leaders of a project that predicted up to 11 degrees of warming, says: “The danger zone is not something that we are going to reach in the middle of this century. We are in it now.”

“It is not too late to save the Arctic, but it requires that we begin to slow CO2 emissions this decade,” says James Hansen, director of Nasa’s Goddard Institute for Space Studies.

Talk of feedback effects and tipping points is still controversial among scientists, however. Tim Lenton, reader in earth systems analysis at the University of East Anglia, is conducting a review of the science of feedbacks and tipping points. He says: “There has been quite a lot of hyperbole around this.”

He says of fears that the Siberian permafrost is melting: “A lot of people are saying there is a positive feedback, which is true, but quite how strong is the feedback? The impression is being given that it’s quite strong but actually it’s quite weak.”

Myron Ebell of the US Competitive Enterprise Institute, a prominent sceptic on global warming, adds: “I don’t think [tipping points are] a scientific concept. It’s a popular cliche that is being used by the alarmists to increase alarm. Mr Gore’s slide show, movie and book use it.”

He continues: “The radiative forcing [temperature- raising] effect of CO2 is not linear but logarithmic. Each increment [of CO2] added will have less effect than the previous increment. Another way of putting this is that each doubling of CO2 results in the same increase in forcing.”

The idea of tipping points has helped galvanise political opinion. Just as climate change itself appears to be gathering momentum, so does the political response. Robert Wyman of Latham and Watkins, a US law firm, says Mr Gore’s film and recent action to curb emissions at state level have had a big effect on public opinion.

To this he adds the effect of “new significant scientific analyses” and “incremental but significant additional political support in the US Senate”, as well as an increasing awareness of energy thanks to high fuel prices. Hurricane Katrina, which devastated New Orleans last year, also seems to have had an impact.

Action on emissions seems to be picking up. Later this month governor Arnold Schwarzenegger will usher in the mandatory curbs on emissions from energy-intensive industries just approved by the California legislature. Seven north-eastern states have agreed a separate initiative to cap emissions from power stations in 2009 and reduce them by 10 per cent by 2019. Some think the federal government may have to follow. Greg Gordon, an analyst at Citigroup, says: “The political will to regulate CO2 emissions in the US is gaining momentum. Federal legislation is likely in the next few years.”

Outside the US, concern over tipping points is also intensifying pressure. In November, the signatories of the United Nations’ Framework Convention on Climate Change – parent treaty to the Kyoto protocol – will gather in the Kenyan capital Nairobi. They will be assailed by non-governmental organisations urging tougher action on emissions after the current provisions of the protocol expire in 2012.

One of the main topics of informal discussion at the meeting will be the fourth assessment report, due out next year, of the Intergovernmental Panel on Climate Change, the scientific study that underpins Kyoto. The draft version of the report suggests that the notion of tipping points and positive feedbacks will play a minor role. It is likely to predict an average global warming of 3 degrees Celsius by 2100.

Though some warn against overstating the feedback effect and the near approach of tipping points, most climate scientists accept the possibility that the climate will change abruptly rather than warm gradually. But this is not adequately taken into account at the highest levels of politics. Mr Lenton, describing this as a serious omission, says the climate is subject to “highly non-linear change”.

He elaborates: “The curve is not smooth, in other words. But the typical economic approach has smooth curves. This is a conceptual shift, from a smooth curve to stepped rises, that if policy-makers could get hold of could transform the way we think about this.”

Copyright The Financial Times Limited 2006

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