Month: September 2013

Population Control

The jury is out on whether the global population will reach 10 billion though there seems little doubt that our planet cannot sustain the current population, never mind 10 billion, with a Western life style.  Maybe some of you saw Stephen Emmott’s show ‘Ten Billion’ at London’s Royal Court Theatre last year; I didn’t but you can read his book of the same title.  As you will probably have guessed from the title, he thinks we are headed for a global population of 10 billion and that radical social and political action is needed because science and technology cannot avoid the impended disaster.  Erle C. Ellis does not believe that overpopulation is problem because he subscribes to Ester Boserup’s theory that population growth drives land productivity.  He suggested in the New York Times last week (13th September 2013) that we have transformed ecosystems to sustain ourselves in the past and will continue do so.

This idea could be extended to suggest that the human society or population is self-controlling that has parallels with the Gaia principle that the planet is self-regulating system in which organisms co-evolve with their environment.  The UN low-fertility model offers some evidence of self-regulation of the human population being to operate because it predicts the global population reaching a maximum of 8.34bn in 2050 and declining to 6.75bn by 2100.  At those levels engineering solutions could probably manage the rest and avert disaster.  Danny Dorling in his book ‘Population 10 Billion: The Coming Demographic Crisis and How to Survive It’ provides further evidence by pointing out that the global average family size has never been so small with the norm being less than one child per woman for more than half the planet and immigration to wealthier countries leading to further declines in birth rates.  If the UN low fertility model is right then perhaps we will be able to avoid overpopulation but  scientists and engineers will still need to redouble their efforts to provide sustainable goods and services.  Progress is being made but mainly through incremental improvements that many of us take for granted perhaps in part due to our ignorance of science and engineering or at least of the advances in living standards that it are being delivered to billions of people who previously did not access to the internet, mobile phones and medicines.


‘Overpopulation is not problem’ by Erle C. Ellis in the New York Times on September 13, 2013 (

‘Crowded Planet’ by Clive Cookson in the Financial Times on July 13/14, 2013

‘Population 10 Billion: The Coming Demographic Crisis and How to Survive It’ by Danny Dorling, published by Constable

’10 Billion’ by Stephen Emmott published by Penguin,,9780141976327,00.html

‘Damn the cynics and embrace the positive’ by Luke Johnson in the Financial Times on August 14th, 2013 or

Stonemasons and skateboards

skateboardWalking through campus last week I saw a stonemason carving small chamfers every 30cm or so around the edge of plinth being prepared to receive a new sculpture.  A few days later there were metal tabs fitted in the chamfers, presumably to discourage skateboarders from using the plinth for acrobatics.  These metal tabs are becoming as common in our public places as the skateboarders they are designed to discourage.  I can understand old people being worried by fast moving youngsters on skateboards, but the speed and freedom of movement is part of the attraction for young people.  As a teacher of engineering, I see the skateboard as another everyday example of engineering with which to liven up the classroom and grab students’ attention.  Try riding a board into class to engage attention!

Below is a ‘5E’ lesson plan for beam bending theory based around a skateboard.  For more on Everyday Examples in Engineering ‘Bridging Cultures’ on June 12th, 2013; and ‘Disease of a Modern Age’ on June 26th, 2013.


Teaching stress

ipodDuring my trip to the US (see post entitled ‘Detroit’, on 21st August, 2013), my earphones for my IPod broke.  This seems to be a common occurrence, perhaps a case of the planned obsolescence I wrote about on May 1st, 2013 under the heading ‘Old is Beautiful’.  Nothing very beautiful or repairable about broken earphones, they are just part of our disposable culture.  However, I collect them and use them when teaching engineering students about stress and strain.  Students have all experienced such a failure and so it is an everyday example of engineering that can be used to teach the principles of stress and strain in a familiar context.  A suggested 5E lesson plan for doing this is provided at the bottom of this post.

The lesson plan deals with the stresses in the earphone cable when the ipod is dangled from them and the discussion in class can be extended to include the stresses induced by spinning the earbuds on the end of the cable or the effect of repeated bending of the cable leading to possible fatigue failure (like when you bend your old credit card back and forth to snap it in half).

For more on Everyday Examples in Engineering ‘Bridging Cultures’ on June 12th, 2013; and ‘Disease of a Modern Age’ on June 26th, 2013.


Risky predictions


Risk is a much mis-understood word.  In a technical sense, it is the probability of something happening multiplied by the consequences when it does [see post on Risk Definition, September 20th, 2012].  Tight regulation and good engineering could reduce the probability of earthquakes induced by fracking and such earthquakes tend not to produce structural damage, i.e. low consequences, so perhaps it is reasonable to conclude that the risks are low because two small quantities multiplied together do not produce a big quantity [see last week’s post on ‘Fracking’, 28th August, 2013].

The more common definition of risk is the probability of a loss, injury or damage occurring, i.e. severity is ignored.  Probability is used to describe the frequency of occurence of an event.  A classic example is tossing a fair coin, which will come down heads 50% of the time.  This is a simple game of chance that can be played repeatedly to establish the frequency of the event.  It is impractical to use this approach to establish the probability of fracking causing an earthquake, so instead engineers and scientists must simulate the event using computer models.  One approach to simulation is to generate a set of models, each based on slightly different set of realistic conditions and assumptions, and look at what percentage of the models predict earthquakes, which can be equated to the probability of a fracking-induced earthquake.  When the set of conditions is generated randomly, this approach is known as Monte Carlo simulation.  Weather forecasters use simulations of this type to predict the probability of rain or sunshine tomorrow.

The reliability of a simulation depends on the model adequately describing the physical world.  We can test this (known as validating the model) by comparing predicted outcomes with real-world outcomes [see post on 18th September, 2012 on ‘model validation’].  The quality of the comparison can be expressed as a level of confidence usually as a percentage.  Crudely speaking, this percentage can be equated to the frequency with which the model will correctly predict an event, i.e. the probability that the model is reliable, so if we are 90% confident then we would expect the model to correctly predict an event 9 out of 10 times. In other words, there would be a 10% ‘risk’ that the model could wrong.

In practice we cannot easily calculate the probability of a fracking-induced earthquake because it is such a complex process. Validating a model of fracking is also a challenge because of the lack of real examples so that establishing confidence is difficult.  As a consequence, we tend be left weighing unquantified risks in a subjective manner, which is why there is so much debate.

If you made it this far – well done and thank you!   If you want more on weather forecasting and extending these ideas to economic forecasting see  John Kay’s article in the Financial Times on August 14th, 2013 entitled ‘Spotting a banking crisis is not like predicting the weather’ [ ].