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or acid rain, but as something that affects everything we do. It is not just an issue which will change how we live in the future, but how we live today.

Increasing evidence has transformed climate change from a potential, long-term issue of uncertain consequences, to an immediate issue of food production, heatwaves, hurricanes, water shortages and the loss of iconic landscapes such as alpine glaciers or species such as polar bears. Indeed, in the latter case we are in an unprecedented historical situation where we for the first time know that a species is probably in effect already extinct; what is left is the endgame as polar bears die out during the next 30-40 years, as the climatic impacts of emissions already produced reap their damage.

The anxiety associated with these events has been reinforced by the growing drip-feed of news stories which appear to confirm our sense that something has irrevocably changed. Each year there is a new piece of evidence. Even just regarding hurricanes, we have a new first almost every year - 2004 giving us the first hurricane ever in the southern hemisphere, 2005 giving us Katrina, the most destructive in modern history, 2007 the first year with two category 5 storms in the same year.

While no individual event can be attributed to climate change, extreme weather events provide timely reminders of what we can expect in a world of accelerated climate change. It may not be sensitive to say so, but it is probably true that unprecedented floods in the UK in 2007, which wreaked havoc across the country, including several deaths, brought home the severity of the issue to people normally protected from the effects of climate change. Certainly more so than the floods in Mozambique the same year, which, while shocking, were ultimately less visible to those in the rich North. Of course, the floods in Mozambique displaced many more than in the UK (the 2007 floods killed around 30 people, while earlier flooding in 2000 killed around 700). But while the rich can protect themselves better from the effects of climate change, they are less and less immune from its effects.

The pressure to recognise the seriousness of the climate crisis has also been built by a flurry of books and films which have summarised recent research and information on the subject for a broad public (and provoked increasingly hysterical responses from climate deniers such as Margaret Thatcher's former Chancellor of the Exchequer Nigel Lawson). With titles like Fieldnotes from a Catastrophe, The Weathermakers, Six Degrees and Heat, such books have deepened the already existing broad consensus for action on climate among public opinion (in rich countries at least), moving it centre-stage in political debates.1 Al Gore's documentary An Inconvenient Truth has been the highest profile of these,2 reflecting the dominance of screen over print in contemporary culture as well as Gore's particular profile as almost US President, long-time campaigner on environmental issues and co-recipient with the UN's Intergovernmental Panel on Climate Change (IPCC) of the Nobel Peace Prize in 2007.

These books and Gore's film summarise the ever-strengthening scientific consensus, but also put in place a number of key pieces in the puzzle that help us realise the severity of the situation. They more or less all talk about the slow-down of the Gulf stream (of course dramatised in the wildly exaggerated climate disaster movie The Day After Tomorrow), changes in El Niño patterns, the acceleration in the collapse of the Greenland ice sheet, melting of permafrost and rapidly diminishing Arctic ice (the cause of the extinction of the polar bears). The latest addition to this list has been the acidification of oceans, an issue which emerged on the scene in 2009. These sorts of changes, occurring more rapidly than anyone thought possible, have given credence to the concern that climate change may indeed make human life on the planet extremely tenuous. The polar bears may be the least of our worries.

To bolster this sense that climate change threatens human civilisation, these books also follow Jared Diamond's lead in re-investigating a series of civilisational collapses that can be associated with changes in climate - the failure of Vikings in Greenland, the collapse of the Akkadians of Sumeria or the Mayan civilisations, the Justinian plague from AD 536 onwards, among others. What is striking here is that all of these historical collapses occurred as a result of (among other things) climate changes significantly less serious than those we are currently in the early stages of. During the century after 1340, global average temperatures declined by only 0.2 °C - this was enough to force the hardy Norse to abandon Greenland. This shift is insignificant compared to the temperature increases already experienced in the twentieth century (around a 0.6 °C rise) and an order of magnitude

1 N. Lawson, An Appeal to Reason: a Cool Look at Global Warming (London: Gerald Duckworth & Co., 2008); E. Kolbert, Fieldnotes from a Catastrophe (London: Bloomsbury, 2007); T. Flannery, The Weathermakers (Toronto: HarperCollins, 2006); M. Lynas, Six Degrees (London: HarperCollins, 2007); G. Monbiot, Heat (London: Penguin, 2007).

2 Though at the time of writing the independently produced film The Age of Stupid, which takes a far more critical look at climate politics, is a success on the independent cinema circuit.

Climate change: from threat ... 5

smaller than those projected for the twenty-first century (between a 1.5 and 4.5 °C rise, according to the IPCC).

The figure of 2 °C higher than pre-industrial temperatures has been widely talked about as a target for the maximum temperature change that human societies might be able to tolerate. The European Union (EU) has even made it a formal aim in its negotiations for the agreement to replace the Kyoto Protocol - the international community's main treaty to date designed to reduce emissions, agreed in 1997 - and they were joined in 2009 by the G8 declaration which said that 'global average temperature above pre-industrial levels ought not to exceed 2 °C'.3 Despite its various weaknesses, the 'Copenhagen Accord', produced at the UN Climate Change negotiations in December 2009, also affirmed this goal.

Two things here are sobering. First, unless you make the most optimistic assumptions about the sensitivity of climate to CO2 changes, this threshold is basically already passed - to achieve this would require CO2 concentrations in the atmosphere which are lower than current levels.4 The organisation 350.org was set up precisely to campaign for policies that aim to reduce overall concentrations to that level, 350 parts per million (ppm). If you make less optimistic assumptions about climate sensitivity and demanding but plausible emissions scenarios, then it's hard to avoid the conclusion that we are likely to be headed for more like 4 °C or even more.

Second, the last time the climate was 2 °C higher than the present was around 129,000 years ago (palaeoclimatologists call this the 'Eemian interglacial period'). At that point, sea levels were 5-6 metres higher than at present, much higher than the 60 cm increase that the IPCC's 2007 report suggested would be the likely maximum.5 So even

3 'World powers accept warming limit', BBC News, see http://news.bbc.co.uk/1/hi/ world/europe/8142825.stm, accessed 9 July 2009.

4 An excellent short explanation of the logic here can be found in A. Dessler and E. Parson, The Science and Politics of Global Climate Change (Cambridge: Cambridge University Press, 2006), pp. 155-8. Briefly, the logic is this: according to IPCC models, to achieve a maximum temperature rise of 2 °C, you can have a maximum CO2 atmospheric concentration 510 ppm if you assume low climatic sensitivity to CO2 concentrations, 370 ppm with a mid-range sensitivity assumption, and only 270 ppm if climate is highly sensitive to CO2 levels. Given that CO2 concentrations are currently at around 380 ppm, we are already past that threshold unless climate only has a lower sensitivity. That we don't yet have the temperature changes is because of the delays in how the atmosphere-ocean system responds to the CO2 increases.

5 See Mark Lynas' summary of this evidence in M. Lynas, Six Degrees: Our Future on a Hotter Planet, (London: 4th Estate, 2007), pp. 71-3.

if we manage to limit temperature increases to 2 °C, we may be in serious trouble. At 4 °C higher, even on the conservative IPCC assessments of a 60 cm sea-level rise (their minimum projected increase for that temperature rise), large areas of cities like London, Boston, New York, Alexandria, Mumbai and Shanghai will be inundated. But in the longer term (the only question is how quickly), with this amount of warming, sea level will rise by between 6 m and 25 m as the Greenland and Antarctica ice sheets melt (the variation depends on how much of Antarctica melts at this temperature). At a 6 m rise, London's flood defence experts suggest that much of London can no longer be defended. But again, the last time the world was 4 °C warmer than today (around 40 million years ago), there was no ice at either pole, and sea levels were more like 50 m higher than today's.6 This is the science-fiction world of J. G. Ballard's 1962 novel The Drowned World, where Greenland is the most habitable part of the planet. The novel is set in London where the spire of St. Paul's Cathedral just manages to peak out above the water level.7

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