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 1800’s and into the 1900’s. However, technological advances in locating and harvesting cod were developed in the 1960’s and the 1970’s. The efficiency of cod harvesting increased hugely and record landings of cod resulted. The cod populations began to diminish. Cod fishermen were forced to go further and further from land to find cod. By the time the cod 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 the 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 in point. The staggeringly large populations of these birds seemed to provide a limitless resource of food. Efficient ways of killing large number of birds led to the carnage of thousands of birds. A highly social species, Passenger Pigeons ceased to reproduce when their populations fell. The demise of the Passenger was rapid and inexorable.

April 20 will be the 45th Earth Day. This day should remind us all to try to tread more lightly on the earth and redouble our efforts at conservation. Let’s think about a third resource that is 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 that conservation biologists seek as the upper tolerable limit. We all know of the 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 the atmosphere 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 birding 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, ME was not on his itinerary). You can read about his Big Year at

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 to ameliorate our fuel consumption and carbon dioxide production. Otherwise, tragedy awaits.

[Originally published on April 13, 2015]