The Climate Bathtub at 25: Expanding a Popular Physical Metaphor to Illuminate Social Challenges of Climate Change

The “climate bathtub,” originated by Linda Booth Sweeney and John Sterman in 2001, has provided an elegant metaphor for the physical problem of climate change for 25 years. In this metaphor, as long as inflows of water into a bathtub from a faucet (greenhouse gas emissions) exceed outflows through a drain (removals), then the stock of water in the bathtub (atmospheric concentrations) will rise, with eventual consequences when the bathtub overflows. This bathtub metaphor is simple, relatable, urgent, and apt. But climate change is a social problem, not just a physical problem. By adding four new elements to the climate bathtub—multiple faucets; multiple drains; multiple damage thresholds; and multiple people—the climate bathtub metaphor can illuminate a wide range of social challenges related to climate change. This expanded climate bathtub metaphor offers insights on how individuals prioritize climate actions; why collective disagreements emerge; and hierarchical levels of climate cooperation. It suggests heuristics that policymakers, practitioners, and future climate professionals can use to evaluate potential climate actions. This more complex, but more versatile, version of the climate bathtub can supplement the original metaphor as a public communications tool and motivator for climate action.