MM 2001: Too hot to handle

As Britain floods, polar ice melts and droughts desiccate great swaths of land, Steve Farrar asks if such global chaos is due to climate change and, if it is, what are we doing about it?

Forest fires and droughts are punctuated by storms and flooding. Another chunk of Antarctic ice the size of Wales makes a bid for freedom from the flanks of the frozen southern continent.

The grim litany of global warming's effects is apparently being visited upon us. Scientists are exploring the wonders of our environment, from volcanic eruptions to bizarre ocean-bed life forms, but one item dominates the environmental agenda - climate change.

This time, society cannot make scientists the scapegoat. How much global warming is due to natural climate cycles and how much to the emission of greenhouse gases is unknown, but the first forest fire was not lit with a Bunsen burner and few lumberjacks sport a lab coat. Instead, society has to look to the scientists it so often lambasts to help deal with the mess others have inflicted upon the planet.

While the task ahead is enormous, elements of the equation are coming together, and significant advances have been made. This is not just a matter of discovering the intricate interrelation of different scientific processes, but of weaving these discoveries into policy issues such as urban planning, fuel pricing, land use and population control. Environmental scientists are switched on as never before to the realities of the modern world, with all the moral dilemmas that entails.

The earth has endured many different climates. During the Cretaceous period, there were no ice caps and dinosaurs roamed Antarctic forests, while just 12,000 years ago, ice sheets covered much of the British Isles. Scientists have probed relics of the past to try to discover what lay behind such extremes. When an international team brought a 3.6km core of ice to the Antarctic surface at the Vostok station in 1998, its delicate layers contained a remarkably detailed record of 420,000 years of temperatures and atmospheric concentrations of the greenhouse gases carbon dioxide and methane covering four ice age cycles.

While this is proving invaluable to climatologists, Paul Pearson, Royal Society university research fellow at Bristol University, says the study's most startling finding was that current levels of these gases seems unprecedented. "When put alongside the modern carbon dioxide rises and the projected increase for this century, it gives very serious cause for concern," he says.

Similar detective work has reconstructed past climates from sediment cores and tree rings. These data enable scientists to theorise about links between shifts in temperature, humidity and sea level and natural processes such as changing ocean currents or the interaction of life with the atmosphere.

A central process is the seemingly eternal exchange of carbon between the living and non-living parts of the global ecosystem. This involves the capture of carbon dioxide in the atmosphere by photosynthesis and its subsequent release through decomposition and respiration. It is carbon dioxide's role as an atmospheric greenhouse gas that is thought to be driving global warming as mankind clears forests and burns fossil fuels.

New facets of the organic carbon cycle and its inorganic counterpart, involving the burial and dissolution of limestones and chalks, are constantly being discovered. One of the more exciting recent discoveries is of iron's role as a key nutrient in the oceans and hence, ultimately, as a mediator in the absorption of carbon dioxide by marine life.

The palaeoclimatologists' data and the analysis of complex systems feed into another key element - climate modelling. At the Hadley Centre for Climate Prediction and Research at Bracknell, supercomputers have enabled scientists to study the influence of factors believed to control climate change while making predictions for the future. Such calculations draw on vast quantities of data on the interaction of ocean and atmosphere to generate their various scenarios.

More flexible though less powerful modelling at Germany's Potsdam Institute for Climate Impact Research has allowed experts to construct scenarios for the impact of different climate changes. A recent Potsdam study by Stefan Rahmstorf focused on past abrupt shifts in the north Atlantic climate, linked to fluctuations in the Gulf Stream. It is possible that global warming could turn down this natural hot tap so that Western Europe cools even as the earth heats up.

So what is likely to happen?

Sea levels have been rising globally as higher temperatures melt the ice caps, making future temperature a crucial area of study. Scientists are also looking at how weather patterns are being altered by climate change and what we might expect - in the United Kingdom this could mean hot dry summers in the south and stormy, wet winters in the north. The provision of clean water to the world's population is yet another issue increasingly influenced by projections of future warming.

How will climate change affect the non-human life on earth? The distribution of some plant and animal populations is shifting in response to changing climate, but man's fragmentation of natural habitats poses an enormous barrier to this.

Robert Meese, a biodiversity expert at the University of California, Davis, United States, predicts that species-level conservation efforts, such as the bid to save the giant panda, will give way to efforts to restore entire imperilled communities. "To lose a community or ecosystem is to lose many, rather than one or a few species," he says.

Just how mankind should respond to the possible ravages of climate change is not a question for policy-makers alone. The ethical debate has many aspects: do we preserve biodiversity out of moral obligation or because mankind needs it, and how can developing countries modernise their economies without being held back by the environmental concerns of richer nations?

However, a cursory glance at the latest publications of the Intergovernmental Panel on Climate Change, where so much of the international scientific output is pooled, clearly shows that the broader ethical picture is not being ignored in the process. It is the task of the scientist to uncover facts without taking sides.

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