Climate change and the "tragedy of the commons"

In 2015, a student tweeted about an extra credit activity in my psychology course, igniting a discussion about the “tragedy of the commons” — the idea that when masses of people engage in excessive consumption, it can have catastrophic environmental consequences, such as climate change. In light of the House and Senate’s recently proposed Energy Innovation and Carbon Dividend Act, let’s revisit this idea and consider how carbon pricing can serve as an effective solution to this problem.

For the class activity, each student was allowed allowed to choose whether they wanted two or six points of extra credit for their grade, but if more than 10 percent of the group choose six points, then nobody received any points. The purpose is to illustrate how a shared resource can be overtaxed (like water or fossil fuels). Only one of the dozens of classes I taught had mastered the exercise. The rest failed, meaning that more than 10 percent of students chose six points, and they ended up with nothing.


Since then, people have prompted me to think about variables that might help mitigate the temptation to choose six points. Then, scaling upward, how could we apply this to stave off overconsumption and put a check on anthropogenic warming?

In 2016, I amended the activity, drawing inspiration from scientists Ernst Fehr and Simon Gachter. Now students have three options to choose from: two points, six points or zero points. That’s right, zero — meaning, they deliberately forego any possible benefit from the exercise. But there’s an upside. For every student who chooses zero points for themselves, another student who had picked six will have their points taken away, and subtracted from the total number of six point choosers. So choosing zero is self-sacrificial, but for the benefit of the whole group.


My courses range from several dozen to several hundred students, and usually a handful choose zero points. This has had a dramatic effect. Since adding this third choice, about half of my classes manage to stay under the 10 percent threshold and receive their extra credit points. Students are cooperating a lot more! Here are the results from my Fall 2018 social psychology course: Out of 119 students, 104 people chose two points, 11 chose six, and four chose zero. Thus, the effective overconsumption rate was under 6 percent. Without the zero-point option, it would have likely been closer to 20 percent, as in years past.

But what about the students who chose zero? Shouldn’t they get a reward for their actions? Well, after the class discussion, I invited students who received two or six points to make a donation to the students who chose zero. This semester, 3 students each volunteered to give one point away to their self-sacrificing peers who had helped make their points possible.

The zero-point option essentially imposes an added cost to choosing six points. When students understood this, more of them opted for moderate consumption. So how do we apply these concepts to stop climate change? One way is through carbon pricing. This strategy treats climate change as a market failure that requires market-based solutions.

The House and Senate recently introduced the Energy Innovation and Carbon Dividend Act, which would place a gradually increasing fee on carbon-pollution. The money collected will be distributed to American families, to manage rising energy costs and help make the switch to renewable energies. This proposed legislation is similar to policies in other nations we normally trade with. It’s also bipartisan, and there are good reasons that both Democrats and Republicans in Congress support it. Liberals may be especially motivated to preserve biodiversity and protect vulnerable populations from the effects of climate change, whereas conservatives may be motivated by patriotic duty to strengthen our country’s national security. Not to mention the fact that carbon emissions are associated with noxious pollutants that contaminate our water and air. Everyone has a stake in this.

By putting a price on carbon, we can effectively reduce overconsumption of fossil fuels, while keeping our country’s economy strong. Polls show that a majority of Americans are concerned about climate change and, in the wake of record-breaking storms, are ready for a “green new deal.”

If we’re going to solve the existential threat of climate change, we need to use all of the tools in our psychological toolkit. This includes recognizing the dilemma we all face between self-interest and loyalty to our American community. People may have a variety of different motivations and values, but in this case, they can all build toward the same common goals.

Dylan Selterman ( is a senior lecturer in the Psychology Department at the University of Maryland.