Correction appended.

The colorful, six-sided tiles with pictures of trees, rocks, and landscapes formed larger hexagons, creating islands across six tables in the second-floor gallery of the Goethe-Institut in Washington, D.C.

On a recent Friday evening, more than 60 people gathered to play a game that has sold 15 million copies worldwide since 1995. The tiles were part of "The Settlers of Catan," a game where players trade and compete for resources while constructing cities. Conversations in the bright room ranged from light banter to tense negotiation as players -- between four and six per board -- vied for land, resources and access to ports.

"The skill of it is choosing which resources to go after," said Matthew Greider, one of the players, who likened the game to Monopoly, but with a board that changes every game. He said there are both elements of strategy -- such as where to place your cities or how you trade minerals -- and luck, as manifested by rolling dice to find out how much of a given resource you receive during your turn.

"There is a certain bargaining aspect to it," said Greider. "You can gouge other players if they are desperate." Resources can then be used to construct roads and villages, which earn points. The first player to reach a certain point threshold wins.

That night at the Goethe-Institut, however, there was a twist. In addition to the classic resources of lumber, ore, wool, brick and grain, gamers could harvest a new commodity: oil.

In this scenario, called "Climate Catan," the new element -- symbolized on a hexagon with a silhouette of an oil pump jack -- allowed players to upgrade their holdings more quickly and increase yields from other resources. But there were downsides. "Using oil produces pollution, as well as climate changing emissions, which bring with them the threat of coastal flooding -- and absolute disaster," warned the new supplemental instruction sheet. Oil could be traded for equivalents in other resources, but there was a finite amount, and reserves would eventually be depleted.

Having oil is good, saving it is hard

At the table near the staircase, the game drew into its third hour.

"Right now, I'm getting more oil than everyone else, so I can advance easily," said Dan Hudner, one of the four competitors. He placed several small, wooden, blue blocks indicating roads between small houses indicating cities, and eyed the other players with suspicion as he hid his resource cards from view. Keeping the other players in the dark about one's own resources helps players gain leverage while trading, explained Hudner. "In certain company, [this game] can get pretty intense," he said.

Initially, Hudner wanted to gather oil and sequester it, or put it aside. In this version of the game, collecting a certain amount of oil without using it earns the player points for environmental stewardship, but not as much as those earned for building expansive cities and roads. "I thought in the very beginning to think about it as if I was actually invested in the environment of the Settlers game," he said, attempting to build his settlements through the traditional routes of slowly gathering bricks and wood while trading for any components he lacked.

However, that strategy was quickly cast aside as the other players began to develop their settlements and competition for resources grew more intense. "Pretty much everyone is trying to get the oil," he said, losing their own incentives to conserve. Settlements and roads soon emerged, scattered along the edges of the hexagons, growing in size and number as players used oil to accelerate development.

Every use of oil turned a counter that would bring the players to a random climate-related disaster once it hit five. Using enough oil would cause complete environmental devastation, and everyone would lose. Within a few turns, the disaster limit was reached and a flood triggered by rising sea levels from fuel emissions washed away coastal settlements, with Hudner's developments largely spared.

"From a very cold, calculated point of view, it wasn't that worrisome for me to use oil and cause a natural disaster," he said, pointing out that his developments were nearer to the center of the island and largely insulated from water-related troubles. "You may be aware about what you're doing to the environment, but if you think it's somebody else that would be affected, you lose a lot of incentive to save the environment," he said.

Fossil fuel use continued unabated in the game as players acquired the oil to convert their cities into metropolises to generate more revenue. A few lucky dice rolls gave Hudner more choice resources, putting him in the lead. With the luxury of sequestering the oil, he gained enough points to win, though the other players were not far behind in their scores.

The downside of 'winning by growing'

Hudner immediately saw how the game's dynamics play out in the real world.

"Developed countries that have already used a bunch of oil have less need for it," he said. "Developing countries still very much need it to continue to develop." In addition, developing countries are more vulnerable to climate change impacts and are less capable of addressing them. For Hudner, the game illustrated how using certain resources, like coal, oil and natural gas, can have individual benefits but shared impacts, like severe weather and soil erosion.

Ty Hansen, one of the developers of the modified game, sat a bit further back from the table, silently observing. He said he was hoping to see "if [the game] is fun and also if people recognize how they treat the real world from this game." Hansen and his co-developer, Eric Assadourian, both avid "Settlers of Catan" players, wanted to make people understand that there are costs to societal development and that there are a number of conflicting demands.

"The one lesson [I want people to come away with] is showing how difficult the politics of climate change are," said Assadourian, who also works as a researcher at the Worldwatch Institute, an environmental sustainability think tank.

More broadly, Assadourian wanted people to re-evaluate how they measure progress. "When you frame something as 'winning by growing,' it's a zero-sum game," he said, pointing out that every player's resource gains come at the expense of another's and deplete the collective pool of materials. "The island of Catan is finite, and the planet is finite. ... We can't keep growing at this rate on a finite planet."

Hansen and Assadourian said they were still tweaking the game and were getting feedback from players. "[The gamers] wanted a 'collective win' option," said Assadourian, similar to the "everyone loses" ecological destruction scenario already in place. However, he worried that this would alter the dynamics of the game and make it less realistic. "Right now, we don't have a way out [of poverty] without growth in the real world," he said.

Overall, the game is "a new way to teach people to consider how they treat the world," said Hansen, who has been playing the original version regularly since it came out in 1995. "It doesn't get old. That's the best part." Hansen and Assadourian have submitted a version of their climate modification for The Settlers of Catan to the game's developer, Catan-GmbH, and its distributor, Mayfair Games Inc., and are working with them to make Climate Catan an official scenario.

Correction: An earlier version of this story misidentified the corporate entity to which Hansen and Assadourian submitted their idea for Climate Catan.

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