Cooperation and Carbon Taxes: confronting the challenges of climate policy with the En-ROADS Climate Solutions Simulator and Princeton’s Energy and Climate Scholars

Written by Abigale Wyatt

The science of climate change is clear, so shouldn’t passing new climate policy be simple? The folks at Climate Interactive have a way for you to decide for yourself: the En-ROADS (Energy Rapid Overview and Decision-Support) climate solutions simulator. According to their website, En-ROADS is a “global climate simulator that allows users to explore the impact that dozens of policies— such as electrifying transport, pricing carbon, and improving agricultural practices— have on hundreds of factors like energy prices, temperature, air quality, and sea level rise.” Practically speaking, it’s an easy and intuitive way to look at future climate scenarios based on the latest climate science. 

Princeton Energy and Climate Scholars (PECS) members exploring the En-ROADS climate solutions simulator. Background left to right: Max Elikan, Maya Chung, Carli Kovel, Marco Rupp, Front: Aaron Leininger, Moriah Kunes.

In October, I introduced En-ROADS to the Princeton Energy and Climate Scholars (PECS), a diverse group of graduate students interested in climate issues from departments all across the university (politics, chemistry, engineering, geosciences, atmosphere and oceanic sciences, ecology and evolutionary biology, and more). I have led these En-ROADS events for the past three years and was excited to share with a group of Princeton students who were really invested in climate mitigation. For this event, I led a role-playing game where players act as climate stakeholders in a simulated emergency climate summit organized by the United Nations (UN). Acting as the UN secretary-general, I called on the group to propose a climate action plan that would keep total global warming under 2 degrees Celsius by the year 2100. Over the course of three rounds of play, the PECS attendees— role-playing interest groups like “Agriculture, forestry and land use” or “Clean Tech”— suggested policy or mitigation strategies to reduce net greenhouse gas emissions that could be implemented in the En-ROADS simulator. 

We started the first round with the baseline scenario in En-ROADS, which results in 3.3o C of warming by the year 2100 (Figure 1). This baseline assumes social and technological progress continues at the current rate, without additional climate policies or action, similar to the “Current Policies Scenario” of the Integrated Assessment Models or the IPCC reports

Figure 1: Dashboard of the En-ROADS simulator, displaying the baseline scenario resulting in 3.3o C of warming by the end of the twenty-first century.

In the first round, each stakeholder group unilaterally proposed one mitigation strategy that aligned with their own priorities, but quickly found issues with this approach. One group proposed subsidizing renewable energy sources and another subsidizing nuclear energy, both with the hope of reducing fossil fuel emissions from the energy sector. Adding a $0.03 /kWh subsidy to renewable energy expanded the energy market share of renewables, thus reducing the more fossil-fuel intensive sources like coal and oil. This change resulted in reducing the projected 2100 warming by a modest tenth of a degree to 3.2o C. However, adding a subsidy for nuclear not only reduced fossil-fuel intensive energy sources as intended, but also ate into the market share of renewable energy. This is because nuclear and renewable energy compete with each other as much as with coal, oil and gas (Figure 1). As a result, adding the nuclear subsidy on top of the renewable energy subsidy had a negligible effect, keeping projected 2100 warming at 3.2o C. This surprising result demonstrated a need for more synergistic mitigation strategies, fueling negotiations between stakeholder groups in the next round. 

Round two saw periods of intense debate between stakeholder groups, as individual actors formed coalitions with two blocs emerging. One coalition, led by “Conventional Energy”, which included “Clean Tech”, “Industry and Commerce” and the “Developed Nations”, proposed investment in technological carbon removal, or carbon capture, to offset emissions. This would prop up the “Industry and Commerce” and “Clean Tech” sectors by increasing funding for research and development without negatively impacting the status quo of “Conventional Energy” and “Developed nations”. Alternatively, the second coalition led by the “Climate Justice Hawks” in coordination with the “Agriculture, forestry and land use” and the “Developing Nations”  focused on reducing methane, nitrous oxide and other greenhouse gas emissions that were more relevant to their sectors. This two-pronged approach resulted in a total 2100 temperature increase of 2.7o C, a significant improvement from the 3.3o C starting baseline, but short of the 2o C goal set out at the beginning of the game.

By the start of the third round, no one had proposed any mitigation strategies that would directly reduce CO2 emissions from fossil fuel burning. This was, in part, to accommodate the strong personalities of the “Conventional Energy” team, who had aggressively lobbied for anything else. However, in the third round, the PECS role-players were encouraged to open the En-ROADS simulator themselves and quickly discovered the power of a substantial carbon tax. 

“We just need the carbon tax to be $100 [per ton CO2]” said one member of the “Agriculture, forestry and land use” team.

“Who’s going to pay the carbon tax?” asked a member of “Conventional Energy”.

The conversation quickly escalated as the groups sparred over which mitigation strategies should be implemented in the final round. In short order, the two blocs became one, with every PECS member gathered around a single table, advocating for their stakeholder interests. Ultimately, with a compromise on the carbon tax, increased energy efficiency, a tax on oil, investment in carbon removal technologies and decreased deforestation, the group argued and laughed their way to the targeted 2o C of warming by 2100.

The event was a great success, and the players walked away with a new appreciation for the various perspectives at play when discussing our climate future. “We need to invest more in research; we need to put money into new technologies,” said one student who thought that negative emissions were a powerful factor in their final scenario. Another student said, “This really validates the “all of the above” energy policy of the Obama era” noting that there are still ways to the 2o C threshold without slashing the fossil fuel industry. In the long run, the PECS members all agreed that the solution was complex, requiring cooperation across sectors and a variety of mitigation strategies, with no “one-size fits all” answer. The En-ROADS Climate Action Simulation worked; it facilitated an informative, engaging, and fun discussion of climate change mitigation and policy.

The roleplaying game is my favorite way to introduce the En-ROADS simulator but Climate Interactive also has other ways of engaging. If you’re interested in bringing En-ROADS to your classroom, group or workshop, check out: or reach out to Abigale Wyatt in the Geosciences department for more information. 

Abigale Wyatt is a PhD Candidate in Geosciences working with Prof. Laure Resplandy to study how ocean physics and climate variability impact surface ocean biogeochemistry. After completing her degree, Abigale will join the team at [C]Worthy, an initiative investigating the efficacy of marine-based carbon dioxide removal, as a postdoctoral research scientist.

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