Sounds Crazy #11 | Count your beans precisely


Is there anything wrong with this number?

Out of context it hard to tell. Running to 8 decimal places it is a very precise number. So much so that if it was a measurement of mass in metric tons the 9 would be precision to 100th of a gram.

If the number represented the weight of an object it would take an amazingly sensitive balance to reliably measure such a weight range to such precision.

Back in the day I used a 7-place balance to record the mass of woodlice offspring [the sort of weird thing PhD candidates have to do to unpick life history theory] and it required a very steady hand with the weighing trays suspended on the thinnest of wires.

The balance could handle the precision but nowhere near the mass range. And it cost a small fortune.

Now let’s consider the number in context.

It appears in this equation:


The number is an emissions factor that converts the carbon in the biomass of trees [CBB,j] into nitrous oxide emissions should the biomass burn in a wildfire.

If a tree is measured and found to contain 4.2 tons of carbon, then this equation claims that should the tree burn in a wildfire, 0.173138658 tons of nitrous oxide will be emitted to the atmosphere.

Now it is hard enough to determine the biomass of a tree to the nearest kilo even if you cut it down into pieces and weighed each one. So to then apply an emission factor with 8 digits after the first zero is bizarre.

It is like weighing out grains of salt on a research grade balance when the recipe calls for a pinch.

Be it woodlice offspring or emission modifiers, the first thing you are taught in high school science class is that the number of digits in a number implies its precision.

0.0412 implies two orders of magnitude more precision than 0.04

It’s called the ‘significant figure’ and is a very important rule in science. The number of digits implies the precision with which the information was recorded. If you write 0.04122349 you imply that that last 9 has real meaning.

If you really can be, need to be, or can prove such precision then fair enough.

And it may be meaningful in the engineering of silicon chips but is meaningless in an ecological estimation on something as large as a tree.

This is a classic example of bean counting gone mad — non-scientists playing loose with the basic rules of science and common sense. It is plain crazy. Unfortunately this kind of misplaced precision is sucking the life out of innovation that could help us understand how the environment works and move us towards sustainability.

Except where would we be without the precise number of beans?

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