UPDATE 02/09/2016: it has come to my attention (thanks Katharine Hayhoe) that the experiment below was first performed by Mrs. Eunice Foote and reported to the American Association of Science in 1856! here is the report (thanks Gavin Schmidt for the link). She even foretold the future "An atmospheric of [carbonic acid gas - CO2] would give our earth a high temperature...".
John Tyndall was perhaps the first scientist to recognise the radiative properties of CO2 in 1859. In recent years the study of the role of CO2 and global warming has moved beyond the physics of CO2 and more frequently we hear discussions of record breaking temperatures or equilibrium climate sensitivity in state of the art computer models. I think it’s quite refreshing though to go back to basics and remember that the theory of global warming is: 1. Over 150 years old; 2. rooted in simple physics (CO2 present in the atmosphere absorbs long-wave radiation that it later releases warming the air a bit).
There are quite a few experiments that you can do at home to demonstrate this underlying physics (e.g. here). Over the last couple of weeks I’ve been gathering the necessary equipment to do one of these simple experiments and this weekend I thought I’d give it go.
Here is a picture of my “experimental set-up” on my kitchen bench
It consisted of two Infrared heat lamps (200W), two plastic drinks bottles, to silicone rubber stoppers, two digital fridge thermometers (with some play-doh to seal the hole in the stoppers), and the all-important CO2 in a can.
I filled one of the bottles with CO2 (the one on the left in the picture of above) and turned on the lamps. Entirely consistent with our understanding of the physical properties of CO2, the extra CO2 in this bottle absorbed more of the infrared radiation from the lamp and subsequently released it warming the bottle more than the one with just air in it.
It doesn’t take someone with a Nobel prize to draw parallels between what is happening in this bottle and what is currently happening to the Earth! So remember: the theory of global warming is quite simple and the question should not be “are we warming?” but “how hot is it going to get?”