A few days ago I listened to a radio replay of the Kenneth Meyer lecture given recently at the Australian National Library by Dr Tim Flannery (webcast here). The topic was, of course, climate change. Flannery has been one of the most persuasive and articulate leaders of the international public discourse on climate change over the past several years. His book The Weather Makers, published in 2005, was one of the first to assemble the scientific evidence on climate change and present it to the general public. In retrospect it is a little shocking to realise first, how long it took for such an account to appear, given what is now becoming clear of the scale and impacts of climate change; and second, how much more critical the picture is now, only three years later.Flannery is well situated to educate the general public on the emerging scientific consensus about climate change. His academic training as a palaeoecologist places him at the centre of the many disciplines required to make sense of the complex scientific data and analysis. His gifts as a speaker and writer are considerable: he is able to present for the general audience the main lines of scientific evidence and its key ideas and findings with clarity and power. A review of The Weather Makers described it as “the Silent Spring of our time.” The reference is appropriate, both in presentation style and in content. After a battering by the scientific critics Carson’s book eventually became the first authentic statement of the modern environment movement, and is still one of its standard-bearers. Flannery’s work on climate change is still in the battering mode, under attacks by a new generation of scientific critics and commercial interests. One can only hope that he, too, with colleagues like the American James Hansen, will ultimately prevail. The alternatives don’t seem to bear thinking about.

Flannery, however, does think about them, explicitly and unblinkingly. It’s not easy to tread the line between realism and hyperbole, and there would be those who would observe some swerving and exploration of blind alleys by Flannery over the past few years. Last year, appointed Australian of the Year by John Howard, in a quixotic (or calculated) political moment, appeared difficult for Flannery, caught between a government fixed on denying climate change and the serious implications of the newly emerging scientific evidence: his public statements mirrored his shock and desperation, as governments around the world continued to dither. Now, however, free of the title and its constraints, and perhaps having had time to assimilate the confronting scientific evidence, he seems to have found his public voice again. This was a fine lecture, important in the public discourse, for both its realism and purpose. On the side of realism, I am reminded of Jack Welch’s business dictum, “See the world the way it is, not the way you want it to be.” That is not to discount the power of vision and imagination but to recognise that we can only start from where we are. And where we are in terms of climate change, Flannery pointed out, is considerably more serious than had been thought even two years ago. The world (or at least that part of it which has concluded that climate change is real and worth worrying about) has been relying for its scientific appraisal on the modelling and projections of the UN International Panel for Climate Change (IPCC). The IPCC has been subjected to sustained attacks by those who believe it has vastly overstated the dimensions and risks of climate change, particularly anthropogenic climate change. Its work is now, Flannery observed, under new challenge, this time by new evidence from present and past events, and not for overstating but for understating. Climate change appears to be happening much faster than any of the IPCC scenarios had contemplated, moving the timetable for urgently required action forward by many decades.

Flannery highlighted two new pieces of evidence in support of this conclusion, one from the present and one from the past. From the present comes the dramatic acceleration of the melting of the Arctic ice. Because of the concentration of the effects of temperature rise at the Poles, the Artic ice, much less extensive than the Antarctic ice, was always predicted to exhibit early warning signs of global warming. The diminishing boundary of summer ice has been observed for at least a decade. The trend, however, accelerated markedly in 2005-2006, and in 2007 jumped to a level that the IPCC models predicted would not occur for some decades. That level has been reached again this year, with the North-West and North-East Passages open and joined for the first time in human history. It now appears likely, from a scientific point of view, that the Arctic ice has crossed the much-anticipated tipping point, where the lower albedo of open water allows the absorption of so much more heat that the winter ice must reform a smaller and smaller scales until it disappears. There now seems to be no intervention that can reverse this feedback mechanism, and the disappearance of the Arctic ice is predicted in a matter of years, not decades. The range of impacts this remarkable event will have on the earth’s biophysical system is still largely unknown.

In a general sense this unpredicted warning points to the central problem of the IPCC modelling, one which the modellers themselves have always recognised. The world climate system is large and immensely complex and operates at the largest scale of global systems. Modelling even the mainly linear evolution of these systems is associated with wide-ranging uncertainties. The non-linear elements of these systems are even more difficult to identify and model. It had always been supposed that there were many more feedback mechanisms operating in the global climate system than had be captured in the IPCC models. In addition, unidentified linkages between sub-systems almost certainly exist. It now appears that these hidden factors are much more widespread and important than had been assumed. The feedback mechanisms seem to be overwhelmingly positive; that is, strengthening of trending directions. The Arctic ice is a graphic demonstration of the need to reconfigure the IPCC models to account for more powerful and accelerated effects.

The second new piece of evidence assembled by Flannery comes from the work of James Hansen and his colleagues, associated with the NASA/Goddard Institute for Space Studies, New York. Hansen, as those who have followed climate change for the past two decades will remember, was the first climate scientist to draw attention to the scale and risks of anthropocentric global warming in his 1988 testimony to Congress. As is also well known Hansen was one of those scientists singled out for attention by the successive Bush administrations in their attempt to diminish the impact of the emerging scientific consensus of the reality and seriousness of anthropocentric climate change. In June of this year Hansen and his colleagues published a paper out of the NASA/Goddard Institute entitled “Target atmospheric CO2: where should humanity aim?” The paper examines the climatic history of the earth over the past 65.5 million years. It conclude that the climate system is more sensitive to CO2 accumulation than had previously been thought. Critical to the analysis are ‘slow’ climate feedback processes that are not included in most climate models, but which profoundly affect predictions. These are such processes as ice sheet disintegration, vegetation migration, and greenhouse gas release from soils, tundra or ocean sediments.

Until now an upper limit of 2 degrees centigrade of global warming has been generally thought adequate to limit its impact. Hansen has argued for an upper limit of 1.7 degrees centigrade to avoid irreversible ice sheet and species loss. This has implied a maximum CO2 level of 450 parts per million. Currently we sit at 385 parts per million. The indication of this analysis has been that, although serious and urgent, there is still time to act to prevent the tipping point being reached and seeding dangerous climate change.

The remarkable and challenging conclusion reached by Hansen and his colleagues in the June 2008 study is that, due to the slow feedback impacts, these numbers are probably not right. The evidence from their study of paleoclimatic systems is that 350 parts per million of CO2 seems likely to be closer to the upper limit of safety, if irreversible ice sheet and species loss, with all their attendant impacts on humanity, are to be avoided. At that figure the global system is already in the dangerous zone—past the tipping point. The first critical question is now for how long this post-tipping point level can be maintained before becoming irreversible. The second is not now only how to slow emissions growth, the target adopted by most of the world’s nations who have recognised the need to set emissions policy, for under Hansen’s analysis this must lead to inevitable disaster. It is how to take existing CO2 out of the atmosphere, as fast as possible, while limiting the current net CO2 balance to zero. The stakes, to indulge in severe understatement, have been raised, for the continued well-being of humanity, and of the species who share the planet with us.

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