The good news is that these probabilities, each tiny on its own, must be multiplied together to calculate the overall risk. Since all the fractional chances stacked up here are extremely small, the multiplied total giving the overall probability of a lethal impact is minuscule. The practical risk could be reduced still further if we have forewarning of an impact.
Asteroid 2004 MN4 – whose notoriety duly earned it a proper name, Apophis – is bigger than the meteorite responsible for the geological feature known as Meteor Crater in Arizona and far bigger than the one that exploded in 1908 with the force of a thousand Hiroshima bombs in the air above Tunguska, razing thousands of square kilometres of Siberian forest.
So why were there not desperate headlines at the time warning of our impending destruction? Because the danger passed almost immediately. With the odds at one in 300, the NASA scientists seemed strangely keen not to alert the world to the danger but to offer reassurance. ‘These odds are likely to change on a day-to-day basis as new data are received,’ they announced. ‘In all likelihood, the possibility of impact will eventually be eliminated as the asteroid continues to be tracked by astronomers around the world.’3
Now, ‘in all likelihood’ is hardly a phrase of scientific precision. What did they mean? The newspapers were certainly puzzled. ‘Asteroid impact alert for 2029? Perceived danger may go down as studies continue’, the Seattle Times repeated dubiously. In fact, as we know, the odds rapidly shortened. But even then, the scientists remained apparently blasé: ‘the odds against impact are still high, about 60-to-1, meaning that there is a better than 98 percent chance that new data in the coming days, weeks, and months will rule out any possibility of impact in 2029.’4 This was a little bit different. But why should new data lean this way? Mightn’t they equally be found to suggest that a collision is more likely?
After all, this does not happen for other statistics, although we might wish that it would. If, in a certain city, you have a one-in-a-hundred chance of being shot, that risk does not disappear as a gunman approaches you. A better analogy is one that omits human malevolence, such as emerging from a junction on to a main road in your car and having to cross traffic going the other way. You can risk the turn when you see another car approaching if that car is going to turn off the main road onto your road. As the car gets closer, you gather more data about it – you see it slow down, indicate, the wheels turn slightly, until at a certain point you are sufficiently sure it won’t hit you to make your manoeuvre. A risk that once seemed great is in this way shown to be less.
Scientists estimate an asteroid’s future trajectory based on observations of its orbit around the sun. Because of observational inaccuracies and limitations in the computer models they use, this path is not a fine line but a three-dimensional swathe of space. Where that swathe overlaps the Earth’s orbit, there is a finite possibility that the asteroid will hit us. But as more data are obtained, the swathe can only become narrowed, and as this happens the likelihood that it now includes the Earth is reduced.
In the case of Apophis, somebody found some archived photographic plates of the asteroid dating from before its ‘discovery’. Measurements from these promptly reduced the risk to zero, although closer examination later revealed a bias in the measurements which meant that the ‘all clear’ should not have been sounded at all. Two months later, the danger was finally eliminated with new data from the Arecibo radiotelescope.
Apophis is not beaten yet, however. Its orbit crosses ours again in 2036 and it is currently given a 5,000-to-one chance of hitting us. This led the popular television astronomer Patrick Moore to predict, in an article on space exploration milestones for the twenty-first century, that in 2028 as the asteroid approaches the Earth for the first time we might send up a nuclear device to deflect it from its course so that it does not score a hit second time around.
Asteroids are a new fear. Until recently, we simply did not know enough about them to worry. Two recent discoveries have changed our perceptions. The first was the scientific confirmation obtained in 1990 that an asteroid strike at Chicxulub in Mexico was the most likely cause of the extinction of the dinosaurs 65 million years ago. The second was the dramatic footage of the comet Shoemaker–Levy 9 breaking up and pummelling the planet Jupiter in 1994. At the same time, improved astronomical observation is enabling us to spot many more, especially smaller asteroids – and realize that they pass very close to Earth. Compare the 3,000 ‘near-Earth asteroids’ known now to only eighteen known in 1981. Methods developed in order to evaluate the impact on human populations of nuclear weapons meanwhile allow us to estimate the damage that would be done if an asteroid did hit.
Now that we are learning more, the impact risk is apparently both rising (as we find more asteroids) and falling (as we discover, one by one, that they are not after all on a collision course with Earth). There has been a large drop in the estimated interval between globally catastrophic strikes. In the nineteenth century, this was put at 281 million years. In 1958, the pioneer asteroid researcher Ernst Öpik (Lembit Opik’s grandfather) concluded that an object 500 metres in diameter – enough to trigger the end of civilization – could be expected every 590,000 years. This has altered to 5–10,000 years today.
These are still low probabilities of destruction, but there remains a disproportionate public fascination in them which may be explained by a number of other factors. Here is a natural hazard with no limit to the scale of its destruction – unlike more familiar terrestrial dangers of earthquake, volcanoes or tsunamis. ‘They are the only credible natural threat to human civilization,’ according to John Lewis.5
Where public alarm is far out of proportion to actual risk, it is hard to judge the effort that should be made to address the risk. Media coverage seldom helps. In 1999, BBC News warned that the Earth is ‘due’ to be struck by a ‘giant asteroid’ and that we must: ‘Invest to avert armageddon’. The piece quoted Lembit Opik, whose humble aim was for the UK to contribute £500,000 towards a global initiative to obtain better astronomical data. ‘If we saw an asteroid hurtling towards us,’ he said, ‘we would get 20 seconds and that’s not even long enough for the Lord’s Prayer. If we make this investment then we would get anything from two years’ notice of an impending impact and that’s long enough to divert the object.’ On the first working day of the new millennium, the British government announced that it would fund a task force to look into the threat, while the then science minister Lord Sainsbury soothed: ‘This is not something that people should lie awake at night worrying about.’6 The major outcome was to set up the so-called Near Earth Objects Information Centre.
Meanwhile, astronomers’ top priority is to log the thousand-plus objects a kilometre or more in size that their calculations tell them must be orbiting within the solar system, even though one-third of them are strictly ‘undiscovered’. Smaller objects are more numerous, and so it is more likely that one will hit the Earth, but the damage they do is less, and of course it is harder to spot them. The chance of any meteorite, even a small one, hitting you personally can be estimated by considering the fraction of the area of the planet’s surface you occupy. The Earth’s surface area is 500 million square kilometres. Seen from above, you take up, let us say, an area about 0.5 metres square. This gives a chance of one in 2 million billion that any meteorite hits you (or the roof above your head), and a chance of one in 300,000 or so that it hits someone somewhere. Perhaps 50,000 meteorites a year reach the Earth weighing 10 grams or more. We would therefore expect one human life to be lost to meteorite strikes every six years on average. Why don’t we hear more about these astonishing injuries and deaths? According to Lewis, the reason is that the death is often erroneously put down to more plausible natural mishaps or explained by superstitious beliefs.
Suppose the worst, and a big asteroid is found that really does have our name on it. Even then, the risk ‘can be mitigated in much more concrete ways than is true of most hazards,’ according to Clark Chapman of the Southwe
st Research Institute in Boulder, Colorado. ‘An impact can be predicted in advance in ways that remain imperfect but are much more reliable than predictions of earthquakes or even storms.’7 With ample warning, people could be moved away from the area of impact.
Launching a nuclear bomb into space to deflect an asteroid from its course is an option under serious consideration. But this carries its own risks. Some regard the supporters of this technological fix as fanatics. In 1994 Carl Sagan warned against the diversion ‘through error or madness’ of a premature nuclear bomb space mission ‘for other, nefarious, purposes’.8 The question we should ask ourselves is this: is the risk of our destruction through such misuse greater than that due to the undeflected asteroid?
An even greater danger, according to Chapman, comes not from a real asteroid but from panic spread by misleading reports of observations or predictions. News of a near-miss by a small asteroid given at short notice would be sure to stoke public apprehension of a real impact, for example. Reports of a scientific prediction (which later proves wrong or to have been misreported) that an impact will occur at a particular time and place would cause intense panic until (and perhaps after) the report was denied.
In the past, such false alarms have been avoided because scientists have kept apparently bad news to themselves until they had information to say that it was not news at all. In future, it is increasingly likely that these alerts will leak out, and we will have to learn to make our own judgements. It is perhaps worth noting, therefore, that at the time of writing, all asteroids known to NASA rank as zero on the Torino scale.9
A Sceptic’s Toolkit
For those not inclined to credulousness, it is easy to be cynical about the media in its presentation of stories involving statistical or scientific information. We would rather encourage scepticism. With this in mind, we offer this toolkit for the interpretation of data or information that come our way:
• Vested interest: ask yourself who has made a particular statement. Why might they have done this? Are we being told the whole story?
• Weasel words: should ring alarm bells – especially emotive ones such as ‘plague’, or ones that put us on a one-way trip to disaster such as ‘inevitable’ and ‘overdue’. It is inevitable that night follows day, but it is not inevitable that there will be a terrorist attack. You can be overdue for a meeting that started an hour ago, but a volcanic eruption, an earthquake or an outbreak of disease is only ever overdue based on arguments of probability. Other words may not have the obvious meaning. Government surveys of the ‘work force’ count anyone who has worked one hour or more in a week, so a boost in the numbers working could be down to children babysitting or students spending an evening behind a bar. Is this what you consider work?
• Surveys: who conducted it? Are they credible? Do they have an obvious motive? Who paid them? Whole fields of study can become unhealthily dependent on funds from one source, whether that source is commercial, governmental or charitable. Were the questions neutrally worded? How big is the sample? Too small, and the result may be skewed. Too big, and the authors may be trying to use sheer weight of numbers to persuade you. Is the sample size and margin of error shown? When a pet food manufacturer says that four out of five cats prefer their product, did they only feed five cats? How were the data collected?
• Figures: try to compare figures. Look at as many of the effects of a change as possible, not just one. Compare the present with the past. Compare one country with another. If the data aren’t there to make the obvious comparison, ask yourself what is being obscured.
• Percentages and actual numbers: people with a story to tell will choose the more impressive way of putting things.
• Anecdote and statistics: fears are spread by word of mouth, press and television reports based on harrowing individual stories; authorities frequently counter these with broad statistics. Meaningful comparison between the two is hard. Both may be ‘true’.
• Graphs and charts: like words and figures, these may be subject to error or deliberate distortion. Don’t automatically believe them because they look technical.
• Timeframe: this is an important factor that words like ‘inevitable’ gloss over. Sea levels are rising, but over a longer period than housing planning cycles, so there is time to adapt. Many data series have a long-run trend, a shorter cyclical variation and then (often erratic) individual data points. Be aware of each so as not to be tricked.
• Why now: ask yourself why the story is appearing now, and whether it would be equally newsworthy at another time. Global warming stories appear more in the summer. Travel fears play well as people set off on their holidays. Sex surveys are often released in time for St Valentine’s Day.
• Defeatism: be wary when told there is nothing we can do about something. Why then are we being told about it? Is it merely to alarm us, or to put us in a state of fear?
• Scare snobs: distrust scares where an elite is trying to deny others advantages they already enjoy, for example environmental and health crises exacerbated by cheap flights, exotic food, private modes of transport, choice in medicine and education.
• Scenarios: many economic and scientific studies model a range of future scenarios. Make sure that the outcome described is not just the worst-case scenario.
• Accentuate the positive: don’t discount the possibility that even if some things are getting worse, others may get better – which negative newspaper stories make it their business to do. It will get warmer in 100 years, but what might human ingenuity have devised by then? New energy sources? Genetically modified human metabolism? Improved photosynthesis? Science fiction, you might say, and so it is – for now. But think what has been achieved over the last 100 years.
• The big picture: it’s bad if 100 people die of bird flu, but in a country of 50 million, this is very few. How many died of everything else?
• A sense of proportion: try to keep one, even if the top brass won’t. Ian Blair, the Commissioner of the Metropolitan Police, insists not only that Islamic terrorism poses a greater danger to Londoners than the IRA ever did, but also that it represents a ‘far greater threat’ than that faced during the Second World War. Does this seem remotely credible, or is somebody just bigging himself up?
During the real war, it’s perhaps worth adding, a government poster advised: ‘KEEP CALM AND CARRY ON’.
Notes
Introduction
1. Andrew Marr, My Trade: A Short History of British Journalism (London: Macmillan, 2004).
2. Charles Mackay, Extraordinary Popular Delusions and the Madness of Crowds (Ware, Herts.: Wordsworth Editions, 1995), p. 214.
3. www.psandman.com.
4. John Allen Paulos, Innumeracy: Mathematical Illiteracy and Its Consequences (London: Viking, 1989), pp. 51–2.
5. According to the quotations expert Nigel Rees, wwwic.btwebworld.com/quoteunquote/p0000149.htm.
6. The Times, quoted in RSS News, June 2006.
7. http://en.wikipedia.org/wiki/GeorgeCarlin.
8. ‘Living dangerously: a survey of risk’, The Economist, 24 January 2004, p. 8.
9. ‘Age of terror scaring Australian children’, The Age, 26 September 2006.
10. Mary Douglas and Aaron Wildavsky, Risk and Culture: An Essay on the Selection of Technical and Environmental Dangers (Berkeley and London: University of California Press, 1982), p. 9.
11. Mackay, op. cit., p. xv.
Chapter 1. Sex, Marriage and Children
THE BIRTH DEARTH
1. ‘Italian women shun mamma role’, www.bbc.co.uk, 27 March 2006.
2. Donella H. Meadows, Dennis Meadows, Jorgen Randers and William Behrens, The Limits to Growth: A Report for the Club of Rome’s Project on the Predicament of Mankind (New York: Potomac Associates, 1972).
3. Paul Ralph Ehrlich, The Population Bomb (London: Ballantine, 1968).
4. ‘World population prospects’, www.un.org.
FAMILY BREAKDOWN
1. ‘Parents l
ive apart to cash in on benefits system’, Daily Telegraph, 16 December 2005.
2. ‘19 Minutes’, Daily Mail, 19 July 2006.
3. ‘A nation of unhappy families’, The Times, 26 February 2007.
4. UNICEF, Child Poverty in Perspective: An Overview of Child Well-being in Rich Countries, UNICEF Report Card 7, 14 February 2007 (UNICEF Innocenti Research Centre, 2007), available at www.unicef-icdc.org/presscentre/presskit/reportcard7/rc7eng.pdf.
5. ‘Marriage rates fall to lowest on record’, www.statistics.gov.uk, 21 February 2007.
6. ‘Mamma’s boys’, Observer, 12 November 2006.
7. ‘Do divorcing couples become happier by breaking up?’, Journal A, Royal Statistical Society, March 2006.
8. ‘How do you keep your teenagers out of trouble?’, Daily Telegraph, 3 November 2006.
9. ‘Marriage maketh man’, The Times, 1 March 2007.
10. See for example www.caci.co.uk and www.experian.co.uk.
THE MARRIAGE SQUEEZE
1. ‘A good man is harder to find’, Newsweek, 2 June 1986.
2. ‘Marriage by the numbers’, Newsweek, 5 June 2006.
3. ‘An iconic report 20 years later’, Wall Street Journal, 25 May 2006.
4. Home Alone?, Unilever Family Report 2005, www.ippr.org.uk, 27 October 2005.
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