Back-of-the-envelope; overview; wood-for-the-trees; read-a-landscape: all merely variations of a basic design, invaluable as a check or guide on direction.
As Niels Bohr was reputed to have said, during one of the less-than-formal gatherings at his Institute of Theoretical Physics: the washing-up water gets a bit grubby in the process, but we seem to get clean dishes in the end – much the same with our physics.
The ability to keep the necessary sophisticated elements of a process within bounds of more far-sighted awareness is essential for society. And what a pity it is that our predominant groups in politics, economics, society, religion, do not currently have that.
We live in a finite world, yet: politicians the world over ignore statesmanship in favour of their return at the next election. Economists advise governments from a model built upon the foundation of that impossibility - growth forever. Society is blinded by “savings”, and during “bargain sales” buy items not needed – and, like Amory Lovins, view what are no more than marginal improvements as solutions. Religions are keen to increase their own in a 2 millennia battle for numbers, in disregard for the pain it causes to individuals and to the ability of “God’s Earth” to continue with adequate support for humanity.
Without some back-of-the-envelope viewing of society at large, Homo sapiens is leaning towards oblivion.
A quarter billion of us at 1000AD; 0.8 billion at 1800; 1.5 billion at 1900; 6.5 billion by 2000 ---.
Our total pressure upon earth systems to provide clean product for, and to cope with waste from, our species has not remained static, but increased in parallel with energy useage.
World water supplies –especially underground supplies which underpin agriculture - are in rapid decline for needs/wants of 6.5 billion people. What will they be like in 2050 catering for the 9+ billion demographers envision? Atmospheric pollution (GHW problems), soil fertility decline, --- continue to escalate while population continues to increase – until it crashes.
It is high time for our blind captains of ships-of-state to take a back-of-the-envelope approach.

Exceptionally good article. I'm 100% with the author on using simple maths rules of thumb (espc from stats) to carve through the bulldust propagated by spin doctors of all persuasions.

It's a shame they don't teach kids the pragmatic application of probability and some elementary game theory to school kids. Most handy at everything from playing cards or the stockmarket to building bridges.

Although I must say that I hadn't heard it expressed as a Fermi problem, the technique described is virtually essential in all sorts of life situations.
I have spent some time trying to explain the approximation technique re large number calculations to my children, and later my grandchildren - an absolute necessity when one notes the reliance on push button calculators. Unless the operator has a ball park idea of the answer, one slip can and often does produce the most outrageous results which simply go unchallenged.

I agree that Fermi type thinking must permeate discussions in the near future. The pressing example is that of ongoing economic growth in a finite world. Optimists appeal to the power of the human spirit while self styled realists say the physics dictates otherwise. The archetypal question was that of the non-visit of super smart aliens from other galaxies; the physical task may just not be achievable. See http://en.wikipedia.org/wiki/Fermi_paradox section 4.2.

I'd go so far as to suggest Howard's political demise is due in part to widespread disbelief in some of his scenarios.

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once , I did a calculation to size a conduit for a liquid , got the optimum diameter to four decimal points ,
an old engineer looked at it and told me that in engineering there is only two sizes to choose from

... too big or too small

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colin, you've got the point, from the engineer's perspective. but you missed it completely from the political aspect. politician's are 'maximising' their command of their environment, while using policies which are bad for clients, us. as long as policy is set by a small group, it will favor the well-being of that small group. this is the fundamental law of life, the biological imperative.

if you want the policies of a society to be directed toward the well-being of the society in general, the society in general must set the policies. that's called 'democracy', my theme song.

the pollies will never work for all of us, any more than hyenas work for wildebeest. when you try to pass the responsibility for your welfare to others, you will be disappointed. no pollie loves you like your mother does. grow up, take responsibility for your own welfare by joining with other ozzies in a demand for democracy.

hah! as if..

unfortunately, ozzies ain't got it, whatever 'it' is, when it comes to democracy. so the lab cage will become ever more over crowded, ever more degraded, finally unlivable, and every step of the way, ozzies will complain about the quality of pollies. step over to the mirror, have a look at the real weak link.