Home Object Activities Contact Who's who How to join NSF How to support NSF What's on Resources Nature and Society Editorial How much faith should we place in mathematical modelling? This question came to mind recently when, in reply to the Garnaut enquiry interim report, climate change minister Penny Wong said that the Government would stick with its election promise to reduce greenhouse gas emissions by 60% by 2050. This cut, let it be said, was a far better target than anything the previous Government had agreed to, but Garnaut had said that bigger cuts were needed, and more urgently. Further, he said that in the interests of equity, Australia should aim to reduce emissions by ninety-five per cent. In general it is a good thing for governments to keep their election promises, but they also need to consider new information. Wong had defended the promised cuts by saying they agreed with the latest IPCC modelling of the climate change situation. Mathematical modelling by the IPCC has improved greatly from one IPCC report to the next one. But it has been pointed out many times that the IPCC itself is hampered by having to get agreement from all the scientists involved and from their governments. It tends to have to lean towards the least worst case, and omit findings that upset the various governments and their agencies. The process takes time, so that by the date of issue reports have often been superseded by new data. Any modelling can only be as good as its inputs. Although the models get continually refined, there is no way we can ever know whether every relevant factor has indeed been included, or that its effects have been accurately foretold. In medicine we are often reminded of the synergistic effects of various medicines when taken together, and the complications lifestyle choices can introduce, leading to unexpected results. Cocktails of pollutants added to the environment can also lead to drastic and unexpected effects. So it is with climate. Many scientists are now openly stating that climate shifts are happening much more quickly than expected. Feedback loops are accelerating as they interact and new ones appear. Instead of relying on the predictions of climate models we need to go back to basics. It is now recognised (though not by everyone) that we cannot go on with impunity digging up fossil fuels, carbon stored underground over millions of years of earth’s history, and put it into the atmosphere without upsetting the balance. Similarly we cannot go on destroying the remaining forests without serious consequences. These things will undoubtedly change the climate. You do not need numbers to understand this point. Numbers are, however, very important when really understood. It is well known that statistics can quite properly be presented in different ways, one that will, say, maximise the risk and another that will minimise it in the public perception. Neither is deceitful, per se, yet the choice can be made to mislead. So statistics and modelling are very useful, but often misunderstood and often relied on too heavily. Luckily the most useful maths needed to understand our current predicament is much simpler, yet it too surprises most people. Take any number and double it and double again, then look at the result. If you start with one, doubling gives you two, then four. Four you can easily see, is greater than the sum of one and two. Try again: take five, ten, twenty, forty. Forty is greater than the sum of five, ten and twenty. Whatever number you choose, each doubling adds more than the sum of all that have gone before. This simple exercise can explain why we must stop the increase in population, resource consumption, pollution. Earth is finite, it cannot cope with ever increasing numbers of people, it cannot grow ever increasing quantities of food, it cannot absorb ever more pollution. What is the problem, some may ask. We are not doubling, just growing by small amounts, one, two, three per cent, maybe. Such low growth in population, or the economy, worries some analysts. Look again: growth of one per cent leads to doubling in seventy years. A growth of two per cent means a doubling in thirty five years. Growth of five per cent reduces doubling time to fourteen years. We do have a problem and it is growth. People who think growth is necessary worry because the birth rate in most countries has gone down, and in some is now below replacement level. This is actually good news for the planet, and should be encouraged. No mention is made of our greatly increased lifespan that means population stabilisation requires lower birth rates. The world is already overpopulated by people and we keep increasing our demands, leaving too few resources and too little space for natural systems to cope effectively. If we want to keep earth as the pleasant, habitable planet it is, then we must give up our obsession with material growth. To keep the planet habitable for humans and their ilk we must aspire to a lifestyle and social organisation that recognises that enough is enough, that we cannot have every material thing we might fancy. As many an old folktale tells us, he who goes on asking for more eventually finds that he has lost everything. That is why our lack of biosensitivity, combined with a lack of understanding of some very elementary maths, is endangering us. We are in danger of losing everything. Jenny Wanless April - May 2008 edition accessible here Back to top ________________________________________________________________
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