The bathtub analogy
To grasp the importance of decarbonisation (both removal and reduction), we need to understand the bathtub analogy. Back in 2008, Dr John Sterman1 at the MIT Sloan School of Management used this analogy to help people better understand climate change.
He explained 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 and eventually, the tub will overflow.
In a similar manner, each year humans 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.
Dr Sterman asked 200 graduate students what they thought needed to be done to stabilize concentrations of carbon dioxide in the atmosphere2.
How far do we need to go in turning off the faucet in order to stabilize concentrations?
He argued that stabilizing the flow of carbon into the atmosphere today won’t stabilize the carbon that’s already there. We are still adding carbon. Just because the inflow remains steady year after year doesn’t mean the amount in the tub doesn’t go up. Inflow (reduction in emissions) and outflow (carbon removal) need to be in balance, and that won’t happen at the current levels of carbon dioxide in the tub, unless the inflow goes down by a lot.
This implies that while carbon reduction should be the first cause of action, carbon removal is equally important. GHG gases in the atmosphere will only stabilize if efforts are made to reduce emissions as well as remove them from the atmosphere.
To understand this analogy better, please watch the video below.