Greenhouse, temperature and Earth Day

It's Earth Day on the 22nd of April, and I thought I'd set up a quick experiment as a talking point. I think conceptually the idea of greenhouse gases causing Earth to get warmer is beyond my 4 year old, but as we've been growing plants in a little pop up greenhouse I wanted to show him what a greenhouse does which will enable him to understand why carbon dioxide and methane are called greenhouse gases at a later date! You could do this with a setup similar to our solar oven from last year (using a single box and cling film, without the foil) if you don't have a greenhouse.

I cut out a couple of planet Earth shapes and then there was some collaborative colouring involving both boys and myself.  This produced one Earth shape to sit on the lawn uncovered, and one to go nearby, also in direct Sun, but inside the little greenhouse. You don't need the Earth to do this, but it made the spot visible and stopped the thermometer being stood on, aside from linking to the Earth Day theme! We put identical thermometers on each Earth shape - ones with a plastic case around them would be better for little kids but I haven't got one.

One thermometer inside greenhouse, and one outside

We talked about temperature, and what temperature water freezes (or ice melts) and the temperature at which water boils. I asked what temperature he thought it was, and he said somewhere between zero and one hundred degrees. He wasn't wrong - in the sun, the uncovered thermometer got to just under 20°C. I asked him to predict whether it would be warmer or colder in the greenhouse and he said warmer. To start with it was actually cooler but after an hour it was almost 10 °C warmer - he was correct!  The Sun warms the air inside, but it can't escape out of the greenhouse, so the temperature gets higher than around the uncovered picture of Earth where hot air can rise and be replaced by cooler air.

Reading the thermometer

We talked about how we needed to look after Earth as we live here and we want it to be a nice place for ourselves and the other creatures that live on our planet! I mentioned that burning fossil fuels like coal and oil causes greenhouse gases to be released into the air and that these act like the little greenhouse, and make the planet warmer. We talked about how this might melt some ice in the Arctic or Antarctic. He didn't hugely engage with this, as I thought was likely, but he did get some practice reading a thermometer, talking about temperature and finding out what the greenhouse does to the temperature inside it!