Imagine a kitchen in a busy household — dirty dishes piled in the sink, leftovers cold on the counter, and utensils strewn about. It’s hard to cook dinner in this situation. In a shared space like a kitchen, it is everyone’s responsibility to keep it clean. And when it is everyone’s responsibility, it quickly becomes no one’s. This is called the “tragedy of the commons.” On planet Earth, like in the kitchen, how we behave affects the way that others can use the Earth.
Though sometimes politically unpopular, scientific data can be intriguing. A recent review paper analyzed 39 environmental impact documents such as research papers, government documents, and industry reports. The scientists were hunting for hard data that would help them determine the most effective ways that humans can change their behavior to protect the environment for present day people and future generations.
Examining the environmental impact of a behavior is called a “life cycle analysis” or a “life cycle assessment.” The researchers used life cycle analysis data when available to determine the environmental impact of 148 different behaviors across 10 countries. In this study, impact was measured in tons of carbon dioxide (CO2) emitted per person per year. Behaviors examined included driving a car, flying in an airplane, investing in renewable energy, purchasing an alternative fuel vehicle, hanging clothes out to dry rather than using an electric dryer, recycling, owning a dog, dietary choices, using energy efficient lamps, family size, and more.
After combing through published scientific studies to determine the carbon emissions of each behavior, they ranked the behaviors into three categories – low-impact, medium-impact, and high-impact. In order to account for differences across geographic areas, the data from each country was analyzed separately (shown in the figure below.) The researchers justified focusing their efforts on developed nations because of their relatively high carbon dioxide contribution to the atmosphere compared to less developed nations.
The researchers found that the four highest impact behaviors across all countries are to have one fewer child (a savings equal to 60 tons of CO2 per year), to avoid air travel, to walk or bike instead of drive (a savings equal to 3 tons of CO2 per year each), and to avoid eating meat altogether (a savings equal to 1 ton of CO2).
Using renewable energy and alternative fuel vehicles were not included in their top four recommendations due to inconclusive studies and were downgraded to “medium” impact. Other medium-impact behaviors would include recycling, eating local, improving home energy efficiency such as heating and cooling, and eating less meat.
Low-impact behaviors include conserving water, buying products with less packaging, composting, purchasing carbon offsets, and using public transportation. The researchers found that the behaviors most often recommended in high school textbooks and government-generated outreach materials were primarily of low to moderate impact.
Other important factors to consider when weighing this evidence is the way the behaviors were defined. The impact of having one less child takes into account the hypothetical child’s behaviors as well as its parents’ behaviors and the behaviors of its potential offspring (grandchildren). Recycling was defined as a full commitment to recycling everything that can be recycled for one year, rather than occasional recycling. Renewable energy use would have a medium impact if 100% of the household’s energy were produced by renewables. Lastly, avoiding meat is only high-impact by completely avoiding it, rather than just eating less.
Solid scientific data is necessary when making such profound recommendations. Feel free to look at the researchers’ calculations for yourself – they are publicly available. Asking the average citizen of an industrialized nation to voluntarily give up meat, have one fewer child, avoid driving, and stop flying is by no means trivial. The potential unpopularity of these recommendations make these standards unrealistic for developed nations. The severe restraint this recommended lifestyle suggests is truly a problem of the commons. The researchers emphasize citizens of Earth to consider these high-impact recommendations, despite their unpopularity.