Over the past two weeks, my colleagues and I at Paradigm Trust have had the wonderful opportunity of spending time discussing Geography with Dr Liz Taylor. Among many other conversations, we’ve discussed the use of cycles (water, carbon and nutrients) for primary aged pupils.
One problem we identified was that our pupils were using the ‘rainforest as the planet’s lungs’ metaphor to infer that deforestation leads to reduced oxygen. Of course it does a bit, but no one is seriously worried that we’ll run out of oxygen. The real big deal is that the rainforest is a carbon sink, storing the carbon which would otherwise be in the atmosphere as CO2.
Following our discussions, I have come up with the following progression model to help pupils understand how carbon enters and leaves the atmosphere and how human activities can affect the flow.
This version of the cycle shows how carbon from the atmosphere is stored in wood, until it is broken down by fungi and other detritivores. I would combine this with a look under some logs.
(Note: to prepare pupils to understand the greenhouse effect, they need to know what if feels like to be inside a greenhouse – by year 3, all pupils should have the experience and be able to talk about the sensations).
I would definitely be looking under some logs in the woods for this one. Detritivores don’t get the curriculum time they deserve.
Pupils will be familiar with food chains by this time. Adding them to the carbon cycle (and also showing carbon released through respiration) shows how carbon reaches a sustainable equilibrium.
(Note: you may choose to introduce the idea of the greenhouse effect in year 4/5. A key misconception to avoid is that the greenhouse effect is a bad thing. Without the greenhouse effect, the Earth would be very much colder than it is now. You may be able to avoid this misconception by describing the current climate emergency in terms of an ‘enhanced greenhouse effect’ – or words to that effect. In effect, we want Goldilocks’ greenhouse effect: not too much; not too little; just right.)
I haven’t drawn in a line showing that plants emit CO2 when they respire too. On reflection, I think I should – it’s a big misconception that plants photosynthesise for the benefit of animals. (Does anyone know the relative amount of CO2 produced in respiration from animals, plants and fungi? I feel a bar model coming on).
In year 5, you can begin to think with the model.
- What happens to the flow of carbon around the cycle when there is deforestation? (There is a double answer to this one – first: the rate of absorption of CO2 decreases – second: much of the cut down wood is burnt, releasing more CO2 into the atmosphere).
- What happens to the flow of carbon is we add more through burning fossil fuels? (Answer: more CO2 enters the atmosphere.
When pupils have understood how to think with the carbon cycle model, they will be better equipped to understand the enhanced greenhouse effect. But that’s another diagram.
I’d welcome any feedback 🙂
An effective way to lay the foundations for the carbon cycle is food chains. You’ll probably want to start local – find a plant with aphids or caterpillars on. Show them the insects and birds which eat them (ladybirds and blue tits are voracious). A bird feeder is helpful to get the birds into the area.
I’d go very local for the carbon cycle to start with – maybe a local woods, or even a garden: the process it she same. It’s easier to base it on a concrete situation. Best option is to go outside to do it. Touch the leaves, caterpillars, woodlice.
The Deforestation Reduces Oxygen Misconception
We’ve found that teachers also have this misconception. I blame the rainforest as lungs metaphor. I tried this explanation on teachers in the week – which seemed to hit home.
Fact#1 The Greenhouse Effect is Good (Until there’s Too Much)
Many people think that the greenhouse effect is always a bad thing. But without it, we’d be living (or not) on a snowball. Better to think about the greenhouse effect like Goldilocks would: not too much, not too little, but just right.
A useful addition to the term is ‘enhanced greenhouse effect’ to show that the normal greenhouse effect is a welcome thing.
Fact #2 Losing a little oxygen won’t hurt… but gaining a little carbon dioxide will.
The Earth’s atmosphere is 21% oxygen. Deforestation and other forms of climate change is likely to reduce this by only the smallest of amounts. Probably barely noticeable. If it ever did become a problem, other effects would have made the planet uninhabitable long before.
The Earth’s atmosphere contains 0.04% Carbon Dioxide. It’s so small that it’s hard to imagine how it could be a problem. If we reduced that number by even a few hundred parts per million, we’d get global cooling. Increasing it is leading to global warming.