Why is the general public not more concerned about the potential consequences of climate change? For many risks, such as the risk of a plane crash, the public is far more fearful than the evidence shows, observes John Sterman, the Jay W. Forrester Professor of Management at the MIT Sloan School of Management. But on the issue of climate, he notes, the situation is just the opposite.
"The science is unequivocal now. It's urgent that we reduce greenhouse gas (GHG) emissions," he says. "That debate is basically over." However, Sterman adds, the public at large remains complacent.
What's behind this puzzling complacency? Sterman's research suggests some clues. In experiments conducted with Linda Booth Sweeney, an educator who received her doctorate at the Harvard Graduate School of Education, Sterman, director of the System Dynamics Group at MIT Sloan, found that even highly educated people have a poor understanding of the basic dynamics of climate change, underestimating how much GHG emissions must decrease to limit the risks of severe climate change.
And if people don't have good mental models for understanding climate change, they may come to faulty conclusions about policy. For example, if people erroneously think that climate change is easily reversible, they may support waiting to see what the effects of climate change will be before taking action to reduce emissions of GHGs such as carbon dioxide.
The bathtub metaphor
To help people better understand climate change, Sterman uses the metaphor of a bathtub. 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.
To test whether people understand these basic "bathtub dynamics," Sterman and Booth Sweeney gave highly educated university students a nontechnical summary of information about climate change drawn from the Intergovernmental Panel on Climate Change, including the fact that carbon dioxide emissions are currently twice the rate of natural carbon dioxide removal.
Study participants were then asked to draw a simple graph showing what GHG emissions and removal rates would have to be to stabilize the concentration of GHGs in the atmosphere by the year 2100.
Surprisingly, most people answered incorrectly -- even graduate students with strong technical backgrounds. Most drew patterns in which emissions stopped growing but remained higher than removal -- in effect, claiming that the water in the tub won't rise even when the faucet pours more in than the drain removes.
The study was published in the journal Climatic Change.
Flawed reasoning not unique to climate change
The errors the study revealed are not specific to climate change. In related research, Sterman and Booth Sweeney found that people generally don't understand systems involving accumulations -- whether those systems are bathtubs, business inventories or the concentrations of GHGs in the earth's atmosphere.
Unfortunately, on the question of climate change, the stakes are extremely high. "There's no purely technical solution to the climate challenge. We have to change the way we think about our personal energy choices," Sterman observes.
"The good news," Sterman said, "is that you don't need to know any math to understand that the level of water in a tub rises as long as you pour water in faster than it drains out. Once people understand that we're pouring greenhouse gases into the atmosphere far faster than they are removed, they are better equipped to understand why we can't wait and see -- why we have to reduce GHG emissions today to protect the world we will pass on to our children."
Want to test your own understanding of climate change dynamics? Try the System Dynamics Group's online Greenhouse Gas Emissions Simulator.