Wednesday, April 18, 2007

Read this. Read this.

In the London Review of Books a lucid and cogent (it's the LRB darling, things can't merely be clear and well argued) essay on climate change. Not just the science, not just the potential consequences, not just the politics, but also the psychology. Very interesting. Not to mention terrifying, in that long dark shadow that is just beginning to fall kindof way.


We deeply don’t want to believe this story. The fourth report of the IPCC makes it clear that we are right not to want to. The Summary for Policymakers is a strange document, one which bears out a comment Norman Mailer once made to the effect that ‘form is the record of a war.’ In this case, the war is that between science and the politics of global warming, which is powerfully present in every line of the SPM, mainly in the form of its total absence. The way the SPM works is that the scientists write a report, and then are put together in a room with representatives of the world’s governments, and between them they agree a text that has full support, the idea being that there is nothing left that can be contested: that the SPM has the full support of all the relevant scientists and their governments. Since the governments in question include the administrations of George W. Bush, King Abdullah, John Howard and Hu Jintao, this is not a straightforward process; in fact there is something heroic about the firm stand the SPM manages to take. The price for this is that the SPM makes no policy recommendations of any kind, a fact which has drawn some negative comment; but the consensus on the basic facts is so remarkable that we can live without the unenforceable policy advice.

The first crucial component of the scientific consensus concerns a figure called the ‘climate sensitivity’. This is the amount by which the climate will grow warmer if the amount of CO2 in the atmosphere doubles. It is not a straightforward figure to calculate because many of the values change as the temperature changes; water vapour, for instance, is an important greenhouse gas, and as the oceans warm, water vapour in the atmosphere increases both in amount and in its greenhouse properties. Arrhenius thought that it would take three thousand years for our activities to double the level of CO2, which in 1750, before the Industrial Revolution, was about 280 parts per million (ppm). By now the level is 379ppm and rising sharply. As the Chinese and Indian economies take off and global levels of CO2 begin to rise even more quickly, it seems a racing certainty that we will achieve that level of doubled emissions some time this century; at which point the ‘climate sensitivity’ will become the most important number in the world. So the fact that according to the IPCC ‘an assessed likely range’ for climate sensitivity can now be given ‘for the first time’ is of more than academic interest. That figure is likely – between 66 and 90 per cent probable – to be between 2 and 4.5ºC. The best estimate is for climate sensitivity to be 3ºC. ‘Values substantially higher than 4.5ºC cannot be excluded.’

The consequences of this are listed pretty dryly in the report: cold days and nights will be warmer and fewer, hot ones hotter and more frequent – this is ‘virtually certain’, i.e. more than 99 per cent probable. Increased frequency of heatwaves and ‘heavy precipitation events’ is ‘very likely’ – 90 to 95 per cent. That means that a greater proportion of rain will come in the form of downpours. There will be more and bigger droughts, more and bigger tropical storms, and more and bigger floods – all ‘likely’, 66 to 90 per cent. The sea level will rise between 18 and 59 centimetres, mainly as a result of the ocean expanding as it warms. Increased melting in the Greenland and Antarctic is not included in these figures because there is not enough of a consensus to include its effects in the modelling. That isn’t reassuring. The Greenland ice sheet holds enough water to raise global sea levels by seven metres – which would mean the end of, for instance, London, Miami, the Netherlands and Bangladesh.

What does the picture painted by the SPM mean? The short answer is that no one knows. Although we know more about many aspects of the climate than we once did, the fact is that we are entering a period of climatic change outside the experience of recorded human history, without a confident sense of what those changes will entail. If the events listed above are the whole of the story it doesn’t seem too bad: hotter days and nights, storms and droughts, sound like things we should be able to endure. The trouble is that the global climate is a system of such complexity that we can’t model in sufficient detail what the effects are. The last time CO2 levels were as high as they are today, in the last interglacial 125,000 years ago, sea levels were between four and six metres higher than they are today – a figure which we can take as a proxy for changes which in most respects are beyond imagining. What would happen if the harvest failed all across Europe or the US or Africa? What would happen if it failed again the next year, and the year after that? What would happen if the rain-and-meltwater pattern in the Yangtze valley, the core of Chinese agriculture, changed? What would happen if the glacial run-off from the Himalayas, which supplies most of India with its water, were to change? What would happen if the behaviour of El Niño were to become so unpredictable that agriculture in the Southern Hemisphere became unsustainable at current population levels? What would happen if those glaciers were to melt away? What would happen if the Gulf Stream (the Atlantic’s ‘meridional overturning circulation’, as it is scientifically known) were to shut down suddenly – the Day after Tomorrow disaster scenario? The prediction is that Western Europe would become 8ºC cooler, about the temperature of Canada. But Canada produces enough food to feed 30 million people and enough grain to feed 60 million. Western Europe has a population of about 450 million. So what would they eat?[†] Hurricane Katrina gave us a glimpse of how quickly a meteorological event can destroy a city in the richest country in the world. We may be moving towards a future in which events like that come to seem commonplace. Anything in the paper today, darling? Not much – oh, all the Dutch drowned.

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