We are all familiar with the terrifying math of climate change — if the planet burns more than 565 gigatons worth of carbon dioxide between now and 2050, there is no hope of limiting climate change to less than two degrees centigrade of increase. Living within that limit means leaving most of the planet’s fossil fuel limits in the ground, where they can’t hurt anybody. But what seems too overwhelming even to contemplate is what that global limit means for a sustainable individual carbon footprint.  565 billion tons of carbon divided by the 37 years remaining until mid century means a limit of about 14 billion tons per year.  Divide that limit by the seven billion souls already living on the planet and you get about two tons per person as the implied individual carbon footprint, including both direct impacts (the one’s we control with our personal consumption choices) and our indirect impacts (carbon impacts from community and government activities, and our place of work).  Since our direct impacts, in general, are about one half of our total footprint, this implies a personal direct footprint of about one ton.

One ton of carbon dioxide is equal to about 100 gallons of gasoline, OR one flight between New York and Los Angeles, OR about one sixth of an individual’s share of an energy efficient three-bedroom single family home.

In June 2015, I gave a talk on personal carbon sustainability at the Waterkeeper Alliance annual conference in Boulder, Colorado (in case you are wondering, yes, I took the train from New York in order to reduce my carbon footprint).  There were about twenty attendees at my session, all environmental leaders in their communities.  At the start of the session, I asked the question “Who believes that every person has an ethical obligation to reduce their individual carbon footprint to a sustainable level, even if the people around them are not?”  Not surprisingly, given the audience, every hand went up.  I then explained the two-tons-per-capita-per-year limit implied by the 565 gigaton limit on greenhouse gas emissions, and what this meant in terms of individual carbon generating activities like driving a car, heating your house, or taking a plane trip.  At the end of the lecture, I asked the question again — whether everyone has an individual ethical obligation to limit their carbon footprint to a sustainable level . . . and only two or three hands went up.

The overwhelming nature of the climate problem tends to do that to people, clouding their judgment on seemingly simple questions of personal ethics.

It seems self-evident that we all have a moral duty to avoid emitting greenhouse gases.  After all, it is a universal ethical principle that one must not act in a manner that causes serious harm to other people.  Greenhouse gas emissions will cause climate change which will cause grievous harm to individuals inundated by rising seas, starved by agricultural collapse in desertifying regions, and victimized by the political instability arising from climate refugees.  Climate harms will also flow broadly among huge populations that may not qualify as climate refugees. Even among people who are not displaced by climate change, rapid deterioration and alteration of familiar natural ecosystems will cause psychological stress and loss of a sense of well-being.  This sort of environmental psychological stress has already been identified in communities of Appalachia where the natural landscape has been torn up by mountaintop removal mining.

Still, the question of climate ethics has spawned an entire academic subdiscipline among professional philosophers (that is, those people, usually employed by universities, who get paid to think about ethical and philosophical questions). Some have come up with arguments against any personal ethical obligation to live with a sustainable carbon footprint, relying on abstract arguments like “there is no duty owed to people who haven’t been born yet” or “no individual’s carbon emissions can be said to cause any other individual’s harm.”  I think these arguments are self-justifying hogwash.  An excellent (but very academic) treatment of the subject, refuting these arguments, is a book by Belgian philosopher Wouter Peeters, entitled “Climate Change and Individual Responsibility.” Peeters argues that non-subsistence, luxury carbon emissions can never be ethically justified.

I would not go that far, since Peeters approach would make driving your fuel efficient hybrid 100 miles to visit a spectacular wilderness park equally “reprehensible” as cruising around town in your Lincoln Navigator just for the fun of driving.  But I think that we all share a personal ethical obligation to live within a carbon footprint that is sustainable — that is, would not interfere with future generations’ ability to enjoy life equally.  What is “sustainable” in carbon terms is a whole other question.  But I think a good case can be made that a four-ton individual carbon footprint for a middle-class citizen of the developed world is sustainable during the next thirty years as fossil fuels are phased out globally (as they must be).