We all know the story of Archimedes in his bath. His theory helps us to understand cause and effect.
The bathtub theory is a useful mental model when thinking about issues like economics and climate change.
For example, check out this simulation from Climate Interactive.
What happens if we cap carbon emissions at current levels? Or continue their growth? Or reduce them? This simple animated simulation of the global carbon system is great for helping people explore the relationship between carbon emissions and atmospheric CO2.