A bathtub's water level represents the total stock of a particular gas in the atmosphere. The inflow from a faucet represents all emissions of this gas, and the outflow through a drain represents its natural removal from the atmosphere. For many years, the inflow has been approximately double the rate of the outflow. To stabilize the gas's atmospheric stock (i.e., to stop the water level from rising), which of the following actions is the minimum necessary?

Analyzing Atmospheric CO2 Dynamics

Planetary Atmosphere Management Scenario

Imagine the atmosphere is a bathtub, where the water level represents the total amount (stock) of CO2. The faucet represents CO2 emissions (inflow), and the drain represents natural absorption (outflow). If the inflow from the faucet is currently twice as fast as the outflow from the drain, holding the inflow rate constant (i.e., stopping any further increase in emissions) will cause the water level to stabilize.

In the conceptual model that likens the Earth's atmospheric CO2 system to a bathtub, match each component of the real-world system to its corresponding part in the bathtub analogy.

Analyzing Climate Policy with the Bathtub Model

Consider a bathtub where the water level represents the total stock of a pollutant in the atmosphere. The faucet represents the inflow of this pollutant from all sources, and the drain represents the outflow as the pollutant is removed by natural processes. Currently, the faucet is adding 10 units of water per year, while the drain is removing only 5 units per year. If a new policy successfully reduces the inflow to 7 units per year and this new rate is maintained, what will be the immediate effect on the water level in the tub?

Consider the atmosphere as a bathtub. If human activities add 9 billion tons of a gas to the atmosphere each year (the inflow), and natural processes can only remove 5 billion tons of that gas per year (the outflow), the total amount (stock) of the gas in the atmosphere will increase by ____ billion tons that year.

A global council aims to first stop the increase of a certain atmospheric gas and then reduce its total amount back to a previous, safer level. Using the 'bathtub' analogy where the water level is the gas's total amount (stock), the faucet is the emission rate (inflow), and the drain is the natural removal rate (outflow), arrange the following policy stages in the correct logical order to achieve this multi-stage goal.

Evaluating System Dynamics Arguments

CO2 Emissions as an Inflow to the Atmospheric CO2 Stock

Cause of Increasing Atmospheric CO2 Stock

Figure 2.19: The Bathtub Model of the Stock of Atmospheric CO2