The uncertainty surrounding climate change argues for action, not inaction. America should lead the way

FOR most of the Earth's history, the planet has been either very cold, by our standards, or very hot. Fifty million years ago there was no ice on the poles and crocodiles lived in Wyoming. Eighteen thousand years ago there was ice two miles thick in Scotland and, because of the size of the ice sheets, the sea level was 130m lower. Ice-core studies show that in some places dramatic changes happened remarkably swiftly: temperatures rose by as much as 20°C in a decade. Then, 10,000 years ago, the wild fluctuations stopped, and the climate settled down to the balmy, stable state that the world has enjoyed since then. At about that time, perhaps coincidentally, perhaps not, mankind started to progress.

Man-made greenhouse gases now threaten this stability. Climate change is complicated and uncertain, but, as our survey this week explains, the underlying calculation is fairly straightforward. The global average temperature is expected to increase by between 1.4°C and 5.8°C this century. The bottom end of the range would make life a little more comfortable for northern areas and a little less pleasant for southern ones. Anything much higher than that could lead to catastrophic rises in sea levels, increases in extreme weather events such as hurricanes, flooding and drought, falling agricultural production and, perhaps, famine and mass population movement.

The heat is on

Sep 7th 2006
From The Economist print edition

Global warming, it now seems, is for real. Emma Duncan (interviewed here) examines the nature of the problem, and possible solutions

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THE world's climate has barely changed since the industrial revolution. The temperature was stable in the 19th century, rose very slightly during the first half of the 20th, fell back in the 1950s-70s, then started rising again. Over the past 100 years, it has gone up by about 0.6°C (1.1°F).

So what's the fuss about? Not so much the rise in temperature as the reason for it. Previous changes in the world's climate have been set off by variations either in the angle of the Earth's rotation or in its distance from the sun. This time there is another factor involved: man-made “greenhouse gases”.

When the sun's energy hits the Earth, most of it bounces back into space. But carbon dioxide and around 30 other greenhouse gases, such as methane, help create a layer that traps some of the heat from the sun, thus warming the planet. And, because of the burning of fossil fuels, which contain the CO₂ that the original plants breathed in from the atmosphere, levels of CO₂ have increased from around 280 parts per million (ppm) before the industrial revolution to around 380ppm now. Studies of ice cores show that concentrations have not been so high for nearly half a million years. At the current rate of increase, they will have reached 800ppm by the end of this century. Given that CO₂ being emitted now stays in the atmosphere for up to 200 years, getting those concentrations down will take a long time.

The first person to spot the connection between temperature and human activity was a 19th-century scientist called Svante Arrhenius. He speculated that emissions from industry could double CO₂ levels in 3,000 years, thus warming the planet. Being a Swede, he thought that was just fine. In 1938 a British engineer called Guy Callendar gave a talk to the Royal Meteorological Society in which he claimed to have established that the world was warming, but he was regarded as an eccentric. The idea of global warming seemed bound for the intellectual dustbin.

Chill out

If interest in climate change was lukewarm in the first half of the 20th century, it went distinctly chilly in the second half, for the good reason that the world was getting cooler. In 1975 Newsweek magazine ran a cover story entitled “The Cooling World” that gave warning of a “drastic decline in food production—with serious political implications for just about every nation on Earth”—a prediction repeated with understandable glee by those who suspect the current worry is just another such scare.

The mid-20th-century blip turns out to have been the consequence of another by-product of human activity: sulphur and other airborne particles that bounce back sunlight before it can hit the Earth, thus offsetting the greenhouse effect. By the late 20th century, efforts to control that sort of pollution were having an effect. The particulate content of the atmosphere was falling, and the world began to heat up once more. The idea of global warming was retrieved from the bin and turned into one of the biggest arguments of our time.

The debate involves scientists, economists, politicians and anybody interested in the future of the planet. It is charged by the belief on one side that life as we know it is under threat, and by the conviction on the other that scientists and socialists are conspiring to spend taxpayers' money on a bogey. It is sharpened by a moral angle—the sense, deep at the heart of the environmental movement, that the consequence of individual selfishness will be collective doom: the invisible hand is a fist, and original sin an SUV.

The argument is peopled by big characters: James Lovelock, a British scientist who believes that mankind has fatefully unbalanced the delicate mechanisms of a world he calls Gaia; Bjorn Lomborg, a hyperactive Danish statistician who believes that scientists are twisting figures to scare people; Arnold Schwarzenegger, the governor of California, whose mission is to terminate climate change; and James Inhofe, chairman of the environment and public works committee in America's Senate, who says it is all nonsense.

Unfortunately, the argument is also fuelled by ignorance, because nobody knows for sure what is happening to the climate. At a macro level, modelling what is one of the world's most complex mechanisms (see article) and projecting 100 years ahead is tricky. At a micro level, individual pieces of data contradict each other. One shrinking glacier can be countered by another that is growing; one area of diminishing precipitation can be answered by another where it is rising.

Ignorance and fear have spawned an industry. Governments, international bureaucracies and universities are employing many thousands of clever people to work out what is going on. Foundations are pouring money into research. Big corporations now all have high-level climate-change advisers with teams of clever young things scurrying around to find out what the scientists are thinking and what the politicians are planning to do.

The establishment of an Intergovernmental Panel on Climate Change under the auspices of the UN was designed to silence the arguments and give policymakers an agreed line on what the future holds. But given how little is known about either the climate's sensitivity to greenhouse-gas emissions or about future emissions levels, that proved difficult. Not surprisingly, the IPCC's latest report, published in 2001, offers a wide range of predicted temperature rises, from 1.4°C to 5.8°C by the end of this century.

This huge range limits the usefulness of the IPCC's findings to policymakers. Nor has the panel's existence quietened the debate. Scepticism about its science and especially its economics has led a number of people to disagree with its findings. Some challenge the evidence that climate change is happening; others accept that it is happening, but argue that it isn't worth trying to do anything about it.

Since that IPCC report five years ago, the science has tended to confirm the idea that something serious is happening. In the 1990s, satellite data seemed to contradict the terrestrial data that showed temperatures rising. The disparity puzzled scientists and fuelled scepticism. The satellite data, it turned out, were wrong: having been put right, they now agree with terrestrial data that things are hotting up. Observations about what is happening to the climate have tended to confirm, or run ahead of, what the models predicted would happen. Arctic sea ice, for instance, is melting unexpectedly fast, at 9% a decade. Glaciers are melting surprisingly swiftly. And a range of phenomena, such as hurricane activity, that were previously thought to be unconnected to climate change are now increasingly linked to it.

This survey will argue that although the science remains uncertain, the chances of serious consequences are high enough to make it worth spending the (not exorbitant) sums needed to try to mitigate climate change. It will suggest that, even though America, the world's biggest CO₂ emitter, turned its back on the Kyoto protocol on global warming, the chances are that it will eventually take steps to control its emissions. And if America does, there is a reasonable prospect that the other big producers of CO₂ will do the same.

But first, to the science, and some of the recent findings that have sharpened people's worries.

This survey, which generated about 118 tonnes of carbon dioxide from flights, car journeys, paper production, printing and distribution, has been carbon-neutralised through the Carbon Neutral Company. The cost was £590; the money was spent on capturing methane from an American mine.