Climate Bathtub - More Faucets?

Climate Bathtub - More Faucets?

Part of our web series "Climate Bathtub Model of Earth's Carbon Cycle"

In the "Climate Bathtub" model of the atmospheric portion of Earth's carbon cycle, the recent era of rising levels of CO2 in the atmosphere can be portrayed in a couple of different ways. Human activities, especially the burning of fossil fuels, have added an additional flow of carbon dioxide to the atmosphere on top of the natural processes which release CO2 into the air. This is typically portrayed as an increased flow of water (representing CO2 emissions) from the bathtub's faucet. Since the inflow from the faucet is greater than the outflow via the tub's drain, the water level in the tub (which represents the amount of CO2 in the atmosphere) rises.

There are, however, multiple sources which emit carbon dioxide into the atmosphere. Natural sources include respiration by plants and animals, decay of dropped leaves and other vegetable matter, dissolution of CO2 from ocean water, and eruptions of volcanoes. Human-caused contributions to carbon dioxide emissions into the atmosphere include fossil fuel burning, cement production, and land use changes. An alternative to turning up the flow from the faucet in the bathtub model is to add more faucets. The net result is the same; more water flows into the tub and the water level rises. The multiple faucet version of the model might, for some students, make more sense or emphasize the actual situation in the real carbon cycle more strongly. We present a two-faucet version of the bathtub animation here, in case you or your students find it valuable. Of course, even two faucets don't accurately portray the numerous sources of CO2 flows to the atmosphere. However, two faucets may, for some learners, help get across the point that there is more than one source of carbon dioxide emissions - making it easier to keep in mind the multiple "flows" in the actual carbon cycle.