10-minute trainer: walk your class along a bar chart of the atmosphere's constituents

The levels of alarm about energy production, and the urging of children to hassle their parents into driving less etc in order to save the polar bears (which happen to be doing very well of late), avoiding temperature rises (which would be beneficial almost everywhere), and reducing CO2 emissions (ditto), and of course reducing the incidence of whatever horsemen of the apocalypse currently appeals to those driven nearly demented by their permanent state of alarm about 'the environment', can all be put into a calmer perspective by constructing a bar chart of atmospheric composition (a stacked barchart, in the jargon) in order to display how little CO2 there is in the air, how little the human contribution is, and how little the difference of even a total cessation in our CO2 production would make.

To make it even more vivid, here is an appealing idea from a poster called 'Wendy', who put this up on a comment thread on Jo Nova's site (comment 64, http://joannenova.com.au/2010/11/mystery-solved-why-the-pr-hacks-exploded-their-credibility/#comments), where I have added some boldening at the end:

'Imagine one kilometre of atmosphere that you want to clean up. For the sake of the discussion, imagine you could walk along it.

The first 770 metres are Nitrogen.

The next 210 metres are Oxygen.

That’s 980 metres of the 1 kilometre. Just 20 metres to go.

The next 10 metres are water vapour. Just 10 metres left to go.

9 metres are argon. 1 metre left out of 1 kilometre.

A few gases make up the first bit of that last metre.

The last 38 centimetres of the kilometre – that’s carbon dioxide.

A bit over one foot.

97% is produced by Mother Nature. It’s natural. It has always been in the atmosphere otherwise plants couldn’t grow.

Out of our journey of one kilometre, there are just 12 millimetres left. About half an inch. Just over a centimetre.

That’s the amount of carbon dioxide that global human activity puts into the atmosphere.

And of those 12 millimetres Australia puts in .18 of a millimetre.

Less than the thickness of a hair. Out of a kilometre.

So in every kilometre of atmosphere, complete with green-house gases regulating the climate – in every kilometre reflecting back and retaining the sun’s heat on earth, just .18 of one millimetre is contributed by Australia’s carbon dioxide emissions.

Now Julia Gillard’s Great Green Tax, the Emissions Trading Scheme is designed to reduce Australia’s contribution by 5%. That’s what it’s designed to do. Gillard wants to reduce our [point] .18 of one millimetre by 5%.

That’s what all the pain is about.

It is simply madness. It’s not based on science. It’s a tax. Finally, a tax on the air we breathe.'

Now that's clearly referring to Australia,  but it would be easy to customise this for each of our own countries, and thus provide an excellent '10-minute trainer' to have up our sleeves to use when opportunities arise.

Some niggles arise over the specific numbers to use, not least because of the huge variability of water vapour levels.  If I take, for example, the Wikipedia estimates of the composition of the dry atmosphere, and add in their estimated overall average of 0.4% for water vapour by adjusting all the other constituents in proportion to their quantities, and then round the figures again for simplicity, I get the following values:

N2                    778 metres 

O2                    209

Ar                         9

H20 vapour            358 cm

Trace gases             42 cm   (of which CO2 is 39cm)

So, be prepared to define and defend your own computations and assumptions.  The numbers used by Wendy assume 1m for water vapour, and this may be more typical for the troposphere ( the estimates given in the Wikipedia link today: 'Air also contains a variable amount of water vapor, on average around 1%'; elsewhere it states levels vary between 1% and 4% near the surface, with an overall value of 0.4%).  The Wikipedia data is imperfect in other ways too, for example there is an excess of something like 57ppm when you add up all the constituent ppms for the dry atmosphere.  I suspect someone merely bumped up the CO2 component to 390ppm from a value of around 333ppm in an earlier table without bothering to make any other adjustments.

A simpler alternative would be to do the example for the dry atmosphere, thereby sidestepping the troublesome water:

N2                    780.8 metres 

O2                    209.46

Ar                         9.32         (adjusted down by 0.02 by me to allow overall total to be 1000)

Trace gases             42 cm   (of which CO2 is 39cm)

Lest one be accused of trying to downplay CO2 by even a tiny amount, perhaps the best way is to start with the current estimate of the global ppm for CO2, and adjust the rest of the constituent ppms in due proportion to make up the totals for either the dry, or the 'average' atmosphere.  In any event, it doesn't really matter for the impact of this 10-minute trainer - the important thing is to know the assumptions or source of  your arithmetic.

Wikipedia link: http://en.wikipedia.org/wiki/Atmosphere_of_Earth