In 1960, the ecologist Garrett Hardin published an influential paper in the journal Science in which he developed the idea of the tragedy of the commons. The notion describes the conflict between self-interest and group-interest in the use of a shared resource. Typically, self-interest results in the overuse of the shared resource, and everyone suffers for selfish behavior.

The cod fishery on the Grand Banks provides a compelling example. This region off the coast of Newfoundland seemed to have inexhaustible populations of cod. Cod had been harvested there in a sustainable fashion throughout the 1800s and into the 1900s. But technological advances in locating and harvesting cod were developed in the 1960s and the 1970s.

The efficiency of cod harvesting increased hugely, and record landings of cod resulted. Cod populations began to diminish. Fishermen were forced to go farther and farther from land to find cod. By the time the population started to decline rapidly, the adoption of regulations on the cod fishery came too late.

That fishery has collapsed, just at is has in the Gulf of Maine, and cod populations have not recovered. The self-interest of each fishing boat to take many cod ruined the fishery for all.

The passenger pigeon provides another case. The staggeringly large population of these birds seemed to provide a limitless resource of food. Efficient ways of killing them led to the carnage of thousands of birds. A highly social species, passenger pigeons ceased to reproduce when their populations fell. The demise was rapid and inexorable.

April 20 will be the 45th Earth Day, which should remind us all to try and tread more lightly on the earth and redouble our conservation efforts. Let’s think about a third resource being subjected to the tragedy of the commons: our atmosphere.

I’ll focus particularly on the continuing rise of carbon dioxide in the atmosphere, stemming in large part from the burning of fossil fuels. The carbon dioxide concentration is now above 400 parts per million, well above the 350 ppm level conservation biologists seek as the upper tolerable limit. We all know of global warming, sea level rise, changes in the severity of weather, and changes in the ranges and abundance of living organisms that this rise in carbon dioxide is causing and will continue to cause at ever accelerating rates.

Our atmosphere is a shared resource, and all humans, to different degrees, are treating it selfishly. The tragedy of the commons strikes again.

To help reduce the rise of carbon dioxide, some birders are adopting the practice of green birding. To cut down on fossil fuel emissions, a green birder birds in local areas, requiring less auto fuel. Better yet, green birders simply walk or bike to locations.

The best green birding story from 2014 involved the Big Year undertaken by Dorian Anderson, a birder from Cambridge, Massachusetts. Traveling only by bicycle, kayak or foot, he managed to see 617 species of birds in the United States. He bicycled over 17,000 miles and visited 28 states (alas, Maine was not on his itinerary). You can read about his Big Year at bikingforbirds.blogspot.com.

I think Dorian’s accomplishments are amazing considering that the all-time Big Year in North America produced 748 species. Neil Hayward drove nearly 52,000 miles, flew over 190,000 miles on 177 flights and sailed on 15 pelagic trips to set that record.

We all enjoy traveling to see birds. But to avert the tragedy of the commons for our atmosphere, we need to use a carbon offset calculator (many are on the web) to find ways we can contribute to forest plantings or other green activities and ameliorate our fuel consumption and carbon dioxide production. Otherwise, tragedy awaits.

Herb Wilson teaches ornithology and other biology courses at Colby College and perches in South China. He welcomes reader comments and questions at:

whwilson@colby.edu