OK, so we all know about large geographic area being compared to Wales, strangely this came up in conversation last week, however my failing memory doesn’t allow me to name the other conversant. Wales has long been used to help people visualise an area, according to the standard go-to source for such facts Wales was first used to portray the rate of the rate of deforestation. Interestingly, the area occupied by Wales (~2 million hectares) was also converted into rugby pitches, for those interested:
1 W = 2 x 10E6 RP (where W = area of Wales and RP = area of rugby pitch*)
* Of course just to spice things up the size of a rugby pitch is not fixed, it being 112-122 by 68 metres depending on the size of the in-goal area behind the tryline.
However yesterday morning I discover (via Liane Bening) that there is a new metric on the block…. amount of ice required for a mojito! This is in reference to the amount of melting Arctic sea ice made available through Greenpeace
However whilst reaching out to reader by giving them a volume they can appreciate there are issues of uncertainty associated with this. Just how much ice does one need for a mojito? this is surely a personal thing….. a large number of variable:-
- size of glass?
- which country are you drinking your beverage? hotter country, more ice….?
- homemade or over the bar?
- I’m sure there are others……
The other units of volume offered include bathtubs, Olympic sized swimming pool and rather bizarrely the Leaning Tower of Pisa….. In this world where uncertainty is high on the agenda some of these units are better than others.
Ultimately, given they have included some actual numbers, we can derive the conversion to volume , thus…..
One bathtub = 0.2 cubic metres (200 litres seems rather small to me)
Olympic swimming pool = 2500 cubic metres (I do not have any problems with this)
Leaning tower of Pisa = 10,500 cubic metres (this must be the total volume occupied by the tower and not considering it as a vessel)
And finally a mojito = 400 mL (this seems to be a very large drink indeed)
+++++++++++ But it doesn’t end here, the story goes on ++++++++++++++
So what other comparative units do we use? as an atmospheric chemist I often refer to the concentration of a gas in the atmosphere as what we call a volume mixing ratio, this makes things easier given the pressure in the atmosphere is not fixed, we always consider the atmosphere as a three-dimensional entity and air moves up and down in it a great deal. Just to complicate things “legislative measurements” made at ground level by city councils etc. are usually in mass per unit volume (eg micrograms per cubic metre) but this is only applicable to the small variation in pressure at the planetary surface and they are measuring for local exposure not long range transport of pollution. Anyway I’m getting sidetracked now. SO how should we portray just how minuscule the amount of benzene, for example, is present at a remote monitoring station is something of a challenge. Benzene is predominantly an anthropogenic emission (natural emissions exist e.g. biomass burning caused by lightning) and it also reacts in the atmosphere so one can conclude that the concentrations which might be observed at such a site will be very low, in fact I’d go so far as to say that less than 50 parts-per-trillion is not an unreasonable number to quote, but what does this equate to…..? a single blade of grass on a football pitch? a single grain of sand in a beach volleyball court? Once again more questions….
- once again what type of grass?
- when in the growing season?
- how big is a grain of sand?
Ultimately a major challenge for anyone trying to communicate environmental quantities is to find something that the non-expert can get a handle on. This might be a bathtub, swimming pool, a nice relaxing rum based beverage. Lest we forget the ‘Microsoft minute’ which is generally accepted to be longer than a standard minute.
There are plenty more if you only have the time and inclination….. http://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement
http://www.guardian.co.uk/media/mind-your-language/2010/may/17/mind-your-language-david-marsh (“Jeremy Clarkson had a point”)
http://www.economist.com/blogs/johnson/2010/06/units_measurement (Israel approx size of New Jersey via CIA)