The bathtub analogy

We’ve talked about where greenhouse gases come from and we’ll cover specific sources in upcoming posts. So why are they such a problem?

The best analogy I’ve seen for explaining why our greenhouse gas emissions, if left unchecked, could cause climate catastrophe is one developed by Dr John Sterman at the MIT Sloan School of Management back in 2008.

Sterman explains the analogy as follows:

Imagine pouring water into your bathtub twice as fast as it drains out. Even though water is constantly flowing out through the drain, the inflow exceeds the outflow, so the water level in the tub will rise. Eventually, the tub will overflow.

Similarly, each year we humans now add about twice as much carbon dioxide to the atmosphere as natural processes remove. Unchecked, the tub will soon over flow - that is, the concentration of GHGs will rise until severe, irreversible climate change is inevitable.

To halt greenhouse gas-induced climate change, it's not enough to stop the growth of GHG emissions. Stabilizing the concentration of GHGs in the atmosphere requires that emissions fall to the rate at which GHGs are removed from the atmosphere - a drop of at least half.

Note that these figures are 15 years old, so in all likelihood the water is pouring into the bathtub even faster (as greenhouse gas emissions have increased) and not draining as quickly (due to increased deforestation).

Sterman also did a study to test people’s understanding of the bathtub analogy and found that people don’t really understand systems that involve accumulations, for example climate change, perhaps explaining why mobilising action to combat global warming has proven difficult.